Some in the pool industry believe that calcium “naturally” releases from a new swimming plaster (cement-based) surface while it cures (hydrates) and hardens under water.  And then that causes the calcium hardness (CH) of the pool water to increase 50 to 200 ppm during the first month or two.  That is a false belief.

The fact is that if the plastering workmanship is performed properly and is of high quality, and the water balance is maintained properly, virtually no calcium (less than 10 ppm) is lost from a new plaster surface.

However, if the tap water used to fill the freshly plastered pool is soft and aggressive, then yes, calcium will be etched from the plaster surface, thereby increasing the CH level of the pool water 40 – 100 ppm depending on how aggressive the tap water is.  And that loss occurs within the first few days.

Also, several improper plastering practices can create conditions that allow calcium to be leached (dissolved) from a new plaster surface by balanced water.  High water/cement ratios, high calcium chloride content, wet troweling, and turning on the fill water too early, allows greater calcium dissolution and loss from the plaster even when chemistry factors are optimal.  As much as 160 ppm of calcium can be lost from the plaster surface within the first 48 hours upon submersion due to these factors, even when the tap water and pool water is balanced. 

If the plaster quality and the chemical factors are both good, it is not true that plaster “naturally” loses calcium from pool plaster.  Calcium levels do not automatically rise, and therefore, low levels of CH of start-up water need immediate correction, and preferably before filling to prevent calcium loss.

A good general recommendation for new plaster pools is to pre-test the fill water, and pre-condition it as needed before it is allowed to come in contact with the new fresh plaster.  Raise the calcium level to a minimum of 200 ppm, the TA to a minimum of 120, and ensure that the LSI is a slightly positive number for the first month.  The main point being; new and soft pool plaster requires a positive LSI for one month to protect it and to prevent a loss of calcium from the surface. 

After 30 days, a typical plaster finish generally has become “carbonated,” which means it is more durable and less soluble.  At that point, the LSI can then be lowered to zero.  If that program is followed, very little calcium will be dissolved from the surface, ensuring a smooth, dense, and more stain resistant plaster surface. 

The “Bicarb” start-up actually facilitates the best and easiest program to obtain a positive LSI of the tap water which ensures that no calcium is removed from a new plaster surface, and no “plaster dust” develops. 

However, this is contingent on the plaster quality being good.  If there is any continued increase in the calcium level (accounting for evaporation or Cal Hypo additions, etc.), it is possible that the workmanship and other practices of the plastering work were sub-standard.

The fact that “plaster dust” forms in newly plastered swimming pools when filled with balanced tap water is evidence that balanced pool water can “attack” (meaning “is aggressive to”) and dissolve certain cement compounds from a pool plaster surface.

Even “scale forming” water, with a Langelier Saturation Index (LSI) as high as +0.5 to +1.0, can attack  (dissolve) soluble calcium hydroxide and calcium sulfate, which comprises about 20 percent of a plaster mix. Calcium chloride, an accelerant, generally added to the mix by the plasterers, is actually the most soluble compound of all and is readily dissolved by balanced water. Therefore, let’s understand that 0.0 (balanced) and slightly positive LSI water, is “aggressive” to those cement components of fresh plaster.

It is calcium hydroxide dissolved from a new plaster surface that is converted into “plaster dust.” After a couple weeks, the surface becomes carbonated (i.e., remaining calcium hydroxide is chemically converted to calcium carbonate), and the general dissolution of calcium hydroxide in the plaster surface stops. (The above issue is why onBalance promotes the “Bicarb” [high alkalinity] start-up method for new plaster pools. It prevents the dissolution of calcium hydroxide and the formation of plaster dust by effecting the hydroxide-to-carbonate conversion immediately and in-surface).

Of course, balanced pool water is not aggressive to, and does not dissolve calcium carbonate, calcium silicates, and calcium aluminates which comprise about 80 percent of new pool plaster.  The important thing to understand is that the LSI predicts solubility and precipitation of calcium carbonate only, not calcium hydroxide.

Even calcium nodules (efflorescence) that form on cracks and delamination sites are evidence that balanced water can leach soluble compounds from within pool plaster.

When severe micro-cracking or localized areas of weak, porous, and deteriorating soft spots on plaster surfaces (due to improper plastering practices), allow pool water to penetrate behind the carbonated surface of cured plaster, even properly maintained and balanced pool water will begin to “attack” or dissolve away more soluble cement compounds that are still present sub-surface. This creates increased porosity in those specific areas of a plaster surface, which then eventually causes the plaster in those areas to turn whiter in color in comparison to the larger smooth dense areas surrounding the white porous spots, highlighted cracks or discolored streaks. 

White soft spots or streaks are sometimes claimed to be “spot etching” or “etching deterioration” by plasterers, and only occurs when the water has been aggressive. The truth is that the severe combination of adding calcium chloride to the mix, excessive amounts of water while troweling, and late hard troweling by the plasterers, is what leads to “spot etching” and a defective plaster surface.

Also, if the water has indeed been maintained in an aggressive condition, then the spotting will definitely appear much sooner, because aggressive water will dissolve the soluble cement compounds in those defective areas far quicker than balanced water would. But that doesn’t mean the aggressive water caused the defect – it merely exploited a defect faster.  In that case, there will also be evidence that the dense plaster surface surrounding the spots has been etched. Absent that, it wasn’t aggressive water that contributed to the white spotting discoloration problem.

The simple empirical evidence that aggressive water doesn’t cause white spotting is demonstrated by the fact that acid washes (the most aggressive treatment of all) and “zero” alkalinity (no-drain acid wash) treatments don’t result in white spotting on good quality plaster. And of course, spotting discoloration has been observed in balanced pools with no evidence of etching anywhere.

On one hand, the National Plasterers Council (NPC) claims that alkaline (positive SI) water during start-up causes a blotchy and smooth gray discoloration you sometimes see in new white plaster pools,¹ and that an acid treatment (zero alkalinity) for a week is necessary to lighten the discoloration.² Yet, hundreds (maybe thousands) of new pools are filled with hard tap water every year and don’t turn gray.  

On the other hand, the NPC also says that aggressive water causes gray (or grey) mottling discoloration.³ Yet the NPC’s recommended “solution” and “remedy” is to perform an acid wash.⁴ Isn’t that evidence that aggressive water doesn’t cause graying? And unfortunately, the above "acid" treatments don’t always lighten the discoloration.

On the other hand, the NPC warns that very aggressive water causes etching of the plaster surface⁵ and that is bad. (That statement, of course, is true).

And incredibly, the NPC also suggests that balanced water with a pH of 7.5, a carbonate alkalinity of 80 ppm, a calcium hardness of 190 ppm, at a temperature of 82 degrees, can cause blistering, cracking, spalling, and delamination of a plaster surface.⁶ Yes, the NPC has deemed such water as aggressive and detrimental to a plaster surface. Of course, that claim is incorrect. The actual causes of those issues are from improper plastering practices.

Interestingly, in 2003, the IPSSA organization sent a letter to the NPC requesting the research data that supported their claims on delaminations and spotting.⁷ The NPC replied that based on advice from counsel, they would not provide that documentation, and would not debate those issues.⁸ Really? None of this is a surprise, because no such data exists.

The NPC has recently adopted the policy that it is important to test the tap water prior to filling new plaster pools to determine if the water is aggressive.⁹ Yet, they stop curiously short by giving no recommendations of what to do if it does prove to be aggressive. They don’t suggest that the plasterer should increase the calcium or alkalinity content of the aggressive tap water and balance it before using it to fill the newly plastered pool. Since new plaster is still very soft and vulnerable after finishing, and water can dissolve and remove some of the calcium from a plaster surface already while it is filling, why is tap water that has supposedly been tested and is known to be aggressive allowed to be used to fill the pool in the first place?

Since the NPC claims that -0.1 LSI water is bad for their vulnerable plaster,¹⁰ why did they remove their acknowledgement that plasterers are responsible for ensuring that the tap water for filling the pool meets their standard?¹¹

Fact: When low calcium tap water (less than 150 ppm) fills a new plaster pool, it can immediately begin dissolving calcium from the surface, both raising the calcium level (and TA) of the water and creating plaster dust. If this is the case, when the service tech tests the new pool water for the first time, he would find the calcium level above 150 ppm and in adequate balance, even according to NPC start-up standards, with no need to add any calcium to the water. That situation (aggressive water), however, does not lead to graying, mottling, or “hydration” (water entrapment) discoloration of white plaster, but rather a mild, general and uniform surface loss. Gray mottling is caused by inferior and/or incompatible materials, high calcium chloride contents in the mix, and late, dry, and hard troweling.¹²

Yet, when some pools develop a random or streaky graying within days of plastering, the NPC blames service techs for causing the graying and the increase in calcium (from the tap water reading to the existing pool water reading) because no calcium was added to the pool during start-up and the water was aggressive!¹³ There is no acknowledgment that plastering in hot dry weather, and/or early filling with soft tap water (that plasterers used to fill the pool) dissolves calcium from the plaster upon contact. And no acknowledgment that a percentage of the calcium chloride added to a plaster mix also quickly dissolves (from the plaster matrix) into the pool water thereby increasing the calcium content of the pool water. But again, aggressive water does not cause blotchy graying in new plaster pools.

And to further contradict and confuse things, adhering to the NPC’s Start-up program results in slightly aggressive water during the first month!¹⁴  The Bicarb start, on the other hand, which we promote, is non-aggressive and eliminates calcium loss from the plaster and results in a very dense and durable surface.

It is curious that the NPC requires such strict (and contradictory) water chemistry standards for the service tech to protect pool plaster, yet on the other hand, the NPC refuses to adopt simple and reasonable workmanship standards for a quality and durable plaster product! No restrictions for water content, calcium chloride, water troweling, early filling, late hard troweling, and weather conditions. The NPC complains that their imperfect work is performed in an “uncontrolled environment,” but don’t even suggest “tenting” pools which could easily control the environmental conditions (hot, dry, cold, wet, or windy weather) while plastering!

To top it off, the NPC has been publicly claiming that the ACI endorses their Technical Manual¹⁵ which is not true. How far is this going to go?

On the other hand… oops, we only have two hands… What’s a service tech to do?

References:

1. Randy Dukes representing NPC at 2012 WPSS class, Techlines 7^th Edition

2. Randy Dukes representing NPC at 2012 WPSS class, Techlines 7^th Edition, 

3. Greg Garrett - NPC Online Newsletter Jan – Feb 2004, Fall 2007, October 31, 2007

4. NPC Technical Manual 7^th Edition Section 6.5

5. NPC Technical Manual 7^th Edition Section 6.6

6. NPC Technical Manual 7^th Edition Section 6.4, Section 6.6

7. IPSSAN June 2003

8. IPSAAN July 2003

9. NPC Bulletin #1

10. NPC Technical Manual Section 6.6

11. NPC Technical Manual 3^rd Edition 1998

12. PCA RX203, ACI 524 Guide, NPC Technical Manual 7^th Edition

13. Greg Garrett - NPC Online Newsletter Fall 2007

14. NPC Start-up Card

15. NPC Technical Manual 7^th Edition - Qualifications

Some of you may have realized that some of the pool industry dosage charts for alkalinity adjustments differ with other charts. Here is why:

Previous to 1994, the dosage charts used in the pool industry for lowering alkalinity using muriatic acid and dry acid (sodium bisulfate) were off about 20% – leading one to use insufficient acid for the job at hand. Dosage charts for raising alkalinity using sodium bicarbonate were also off, by about 7%.

In a research report (published by Service Industry News in their March 11, 1994 issue), onBalance members (back before onBalance existed as such) announced to the industry both the error, the correct dosages, and why the errors existed! Most publishers of dosage charts changed their material in accordance with our corrections… but a couple to this day has not done so.

“Muriatic” acid is a slang term for hydrochloric acid, or a solution of water and HCl. The specific strength of acid we use in the pool industry is 31.45% HCl. However, the strength commonly used in laboratory applications, sometimes referred to as “concentrated” HCl, is 37%. About a 20% difference. Hmmm…

Previous to our research publication, the commonly quoted dosage for lowering alkalinity by 10 ppm in a 20,000 gallon pool was 1.3 quarts. Our chemical calculations showed that the correct dosage was 1.6 quarts – a 20% difference. Are we sensing a pattern here?

Apparently, sometime in the past someone asked a chemist to figure up a dosage chart for “muriatic” acid in pool water. He pulled his technical sheet off the shelf, and figured the chart on lab acid – not pool acid. Then perhaps, this chemist used his incorrect acid chart to do a conversion for dry acid dosages, which is also more than 20% off.

The sodium bicarbonate, or baking soda charts, as mentioned, used to be about 7% off – this time telling you to add too much for the effect needed. Of course, overdosing sodium bicarbonate is not particularly detrimental, only resulting in a slight overshooting of the alkalinity and 7% isn’t that much… however the correct dosage charts will say 2.8 pounds for a 10 ppm alkalinity increase in 20,000 gallons, where the old charts will say 3.0 pounds and some say to add 3.3 pounds, an 18% error.

So if your dosage chart of choice calls for 1.3 quarts of acid for 10 ppm in 20,000 gallons (instead of the correct 1.6 quarts), and/or calls for 3.0 pounds of sodium bicarbonate for 10 ppm in 20,000 gallons (instead of the correct 2.8 pounds) – change charts!

Below are some formulas used to calculate the dosage for various swimming pool chemicals.

SIMPLIFIED  FORMULAS for CHEMICAL ADDITIONS to POOLS

Lowering Total Alkalinity with Muriatic Acid:
(Volume of water in pool ÷ 125,000) X ppm desired decrease = quarts to add

Lowering Total Alkalinity with Sodium Bisulfate:
(Volume ÷ 47,000) X ppm desired decrease = lbs. to add

Raising Total Alkalinity with Sodium Bicarbonate:
(Volume ÷ 71,400) X ppm desired increase = lbs. to add

Raising Total Alkalinity with Sodium Carbonate:
(Volume ÷ 113,200) X ppm desired increase = lbs. to add

Raising Total Alkalinity with Sodium Sesquicarbonate:
(Volume ÷ 80,000) X ppm desired increase = lbs. to add

Sodium Hypochlorite: (Volume ÷ 30,000) X ppm desired increase = quarts to add
(Based on 10%/weight – this can vary slightly based on the strength and age of the product - approximation)

Calcium Hypochlorite: (Volume ÷ 78,000) X ppm desired increase = lbs. to add
(Based on 65% av Cl)

Calcium Hypochlorite: (Volume ÷ 60,000) X ppm desired increase = lbs. to add
(Based on 50% av Cl)

Lithium Hypochlorite: (Volume ÷ 42,000) X ppm desired increase = lbs. to add

Trichlor: (Volume ÷ 108,000) X ppm desired increase = lbs. to add

Dichlor (56% av Cl): (Volume ÷ 67,200) X ppm desired increase = lbs. to add
Dichlor (62% av Cl): (Volume ÷ 74,400) X ppm desired increase = lbs. to add

Sodium Sulfite: (Volume ÷ 67,250) X ppm unwanted chlorine = lbs. to add
(Amount in pounds to reduce excess chlorine)

Sodium Thiosulfate: (Volume ÷ 117,600 X ppm unwanted chlorine = lbs. to add
(Amount in pounds to reduce excess chlorine – based on 100% sodium thiosulfate pentahydrate)

Calcium Chloride: (Volume ÷ 83,300) X ppm desired increase = lbs. to add
(Amount in pounds to increase calcium hardness with 77% calcium chloride strength – use 101,700 as divisor for 94% strength)

Cyanuric Acid: (Volume ÷ 120,000) X ppm desired increase = lbs. to add
(Amount in pounds to increase cyanuric acid – based on 100% cyanuric acid strength)

Borax: (Volume ÷ 17,800) X ppm desired increase of boron = lbs. to add
(Based on using sodium tetraborate pentahydrate to increase ppm of boron

When calculating the Saturation Index (SI), does a single low water parameter such as calcium hardness (CH), or a low carbonate alkalinity (C-ALK), make the water automatically aggressive to pool plaster, even when other water parameters are high enough to balance the SI? 

To answer that question, an experiment was conducted. Two quality pool plaster coupons were made and cured in balanced water for 90 days.  At that point, plaster coupon #1 was placed into SI balanced water, but with a low CH of 90 ppm.  The C-ALK was maintained at 110 ppm and the pH from 7.9 to 8.2, which off-sets the low CH and achieves a balanced SI of -0.1 to +0.2.

Coupon #2 was also placed into SI balanced water that had only 45 ppm of C-ALK.  The CH of this water was 360 ppm and the pH was maintained between 7.7 and 8.0, off-setting the low C-ALK and achieving a balanced SI of -0.1 to +0.2. 

After six months in the water, the coupons were removed, and the water they were in was tested for the calcium content to determine if any dissolution or etching of plaster surface material occurred. Of course, any increase in calcium from the submersion water’s starting point would indicate that calcium had been dissolved from the coupon, which was the only available source of additional calcium.

The result? There was no increase of calcium in either water container.

Therefore, these results indicate that if the calcium hardness or the carbonate alkalinity is low, but the water is still determined to be SI balanced, the water is not aggressive.  This indicates that the SI is applicable for plaster swimming pools.

This experiment was conducted because some in the pool industry claim that pool water with a low CH or a low C-ALK is automatically aggressive despite what the SI actually is.  Often, when a new pool plaster surface has undergone severe gray mottling, white spotting, streaking discolorations, flaking, nodules, or other defects actually attributable to plastering errors, the finger is pointed at aggressive water chemistry instead. Specifically, a CH or C-ALK below the APSP “Ideal” minimum is blamed, even in cases where the actual LSI is balanced.

It is interesting to note that the current National Plasterers Council (NPC) 7^th Edition Technical Manual states that if any isolated, individual water parameter (pH, C-ALK, or CH) is lower than the “Ideal” range as defined by the APSP, the water is aggressive.  Therefore, the NPC is (incorrectly) stating that when the C-ALK is less than 80 ppm (while the total alkalinity may be above 80 ppm), or when the CH is less than 200 ppm, or when the pH is below 7.4, (which are the lower ends of the APSP’s “Ideal Standard”), the water is automatically aggressive and considered to be detrimental to the plaster finish (even though the SI may be balanced). 

This is a complete departure from the NPC text on this topic in their 5^th Edition of the Tech Manual.  It stated that pool water needed to be within the “acceptable tolerance” range as established by the APSP, which set the “minimum” for C-ALK at 60 ppm, CH at 150 ppm, and a pH of 7.2. It is apparent that the water balance requirement by the NPC is more restrictive now.  Why did the NPC make that change?  Where is the study documenting that a low CH or C-ALK is automatically aggressive when the LSI is 0.0 or higher?  Has the National Pool Industry Research Center at Cal Poly (NPIRC) proved that?  No.

Now, we are not necessarily promoting the concept that pool water should be maintained on a regular basis with the pH, C-ALK or CH below the minimum APSP targets. We are not even suggesting that the ranges below the ideal are always the optimum. We would recommend that pH and C-ALK levels be maintained above the ideals, not below, whenever possible. However, we understand two things: that there are times when lower pH, CH or C-ALK are unavoidable, and that chemistry is chemistry – the SI “balance” means exactly that… it is not a tool for blaming plaster defects on water chemistry.

As the above plaster study demonstrated, pool water with a single low water parameter (even below the APSP’s “Ideal” or “Minimum” standard) can be non-aggressive if the SI is balanced. 

onBalance

Gray Mottling Plaster Discoloration #5

This fifth article provides additional evidence that gray (or grey) mottling discoloration (which often takes several months to develop) is caused by improper plaster workmanship.

In 2003, the National Plasterers Council (NPC) commissioned the National Pool Industry Research Center (NPIRC) at Cal Poly in San Luis Obispo to conduct research experiments on plaster degradation, discoloration, and other durability issues. The second phase of their studies (2004-2005) consisted of twelve pools being plastered with one-half of each pool troweled with a small amount of water added to aid in lubrication of trowels and with the other half troweled without any water added. 

The reason for this comparison was because the NPC wanted to prove that adding a little water to lubricate the trowel didn’t cause “etching” (although no one has claimed that it does) and that adding water during finishing was okay to do, even though the cement flatwork industry strongly discourages it.

While the study didn’t reveal significant differences between the two sides on the issue of etching, interestingly, it was observed in the balanced pools that the “no water added” side had significantly more discoloration than the “water added” side.  Also, Pool 8, the aggressive pool, did not develop as much discoloration in comparison to most of the balanced pools.  These inspections were performed several times over the course of eight months.

Despite the known fact that troweling when cement and plaster is somewhat hard or dry can lead to discoloration, the Cal Poly professors did not make this a topic of discussion in the “Conclusions and Recommendations” section of their report.

Instead, their report (incorrectly) concludes that “wet troweling” is okay to do, and suggested (without proper scientific evidence) that most plaster problems, (including discoloration, deterioration, and craze cracking), were caused by aggressive water chemistry, salt pools, borates, or (supposedly) inaccurate test kits.

Also conspicuously missing from the NPIRC study was an inspection to determine the amount of discoloration on the plaster coupons with high contents of calcium chloride added (2% to 5%), which is also known to cause graying of cement. Once again, the NPIRC avoided implicating defective plaster or workmanship.  Does anyone believe that something is not amiss with this research?

Consider this; some plasterers occasionally use high amounts of calcium chloride to accelerate the hardening of pool plaster in order to finish their work quicker.  When doing so, the plaster mix may sometimes harden so fast that finishers end up performing late, hard, and dry troweling, and perhaps add excessive amounts of water to compensate and get the plaster surface smooth.  According to research by independent cement laboratories and the American Concrete Institute, that is a recipe for causing darkened or gray mottling discoloration, which sometimes also develops white “soft” spotting or streaking along with the graying. 

Since the completion of the study in 2005, there has not been an admission by the NPC regarding the incomplete or misinterpreted data involved in the above results from their study. As an industry association, the NPC should acknowledge that graying and streaking can be caused by improper workmanship, and should not be suggesting that the NPIRC has proven that aggressive water chemistry or improper chemical start-ups cause this discoloration.

The NPC should be a leader and adopt standards that will promote quality plaster work that will improve the durability and cosmetic appearance of the popular and economical white plaster pools. They should be educating their members on proper workmanship techniques. They should stop suggesting that white plaster is inherently weak and can’t withstand “imperfect” water balance chemistry. Yes, Quartz and Pebble pools can be more durable, but they are more expensive and can also experience discoloration and other similar defects from poor workmanship and/or materials.

onBalance

This article provides the basis and evidence for the recommendations to wait at least 6 hours before filling new plaster pools, using a low water/cement ratio for a plaster mix¸ and reducing the amount of calcium chloride added (one percent or less). Builders, Service Techs and Pool Plasterers can work together to ensure a quality plaster job that will last a long time and be stain resistant. Pool owners want and pay for a quality product.

Several experiments were performed, and first studied were the effects on the length of time one waits after a new plaster pool’s final troweling until the time water is turned on to fill the pool.

For this experiment, plaster was mixed, and coupons were formed and placed in water at various time delays (30 minutes, 2 hours, 6 hours, and 24 hours) after the final hardening.

Each plaster coupon was placed separately into a five-gallon tank of balanced water, a starting pH of 7.7, alkalinity of 110 ppm, calcium hardness of 180 ppm, and a temperature of 70 degrees.

Since this water is balanced according to the Langelier Saturation Index, does this mean nothing from the plaster surface should dissolve into the water?

Of course, we all know that “plaster dust” often forms in the water, and on the walls and floors of pools soon after newly finished plaster pools are filled. And the primary source of this “plaster dust” is, well, the plaster! But why does the plaster come off the walls when the water is balanced to begin with? And why do some pools have more “dust” than others? What can be done to reduce this problem? Those questions will be answered below.

If the chemistry changed in the water after the plaster coupons were placed in the water tanks, it would be assumed as a result of plaster components dissolving and influencing the water chemistry. We also wanted to know if those changes varied according to the “fill delay”.

The first thing noticed was that the pH of the water rose (in 24 hours) in all four tanks. But the pH rose to 8.5 in one tank, and went as high as 9.2 in another. We also noticed some “plaster dust” settling at the bottom of the tanks.

Why did the pH rise so high?

Why did the pH rise to different levels in the different tanks?

Why didn’t the pH stop increasing once the pH reached 8.4, as it would normally?

Since at a pH of 8.4 the calculated Saturation Index of the water would be +0.7, the water isn’t aggressive to the plaster surface, yet the pH continued to go even higher! Where did the pH-increasing influence come from?

The reason for the continuing pH rise in this experiment is the compound calcium hydroxide, a component of hardening plaster, which has an extremely high pH – in the 12 range. It is somewhat soluble even in what we would consider balanced water, since water balance and the Saturation Index is relative to calcium carbonate, a lower-pH compound.

This experiment demonstrates that calcium hydroxide can be dissolved by “balanced” water from the surface of relatively hard plaster. However, calcium carbonate, a major component of a plaster surface, requires aggressive (SI) water to dissolve. The Saturation Index indicates when water has the ability to dissolve calcium carbonate, not calcium hydroxide.

After placing plaster coupons into water at different time intervals after final hardening, we tested the pH of each tank 24 hours after placement. We found that the lowest pH increase (to about 8.5 from a beginning pH of 7.7) was the tank with the coupon that had hardened the longest (24 hours) before placement in water.

The six hour coupons (placed in water after six hours) resulted in a pH increase to about 8.7.

The coupons placed in water after two hours resulted in a pH of about 9.0.

The highest pH increase (to about 9.2) was recorded in the water tanks that received the first plaster coupon in the shortest time, after only 30 minutes after final hardening.

CONCLUSION #1 – The rising pH levels indicated the loss of calcium hydroxide from the plaster surface and into the water.

CONCLUSION #2 – Since the water’s pH change varied progressively from tank to tank, from fill delay to fill delay, we can conclude that the sooner the plaster is placed under water, the more plaster material is dissolved off the surface and into the pool water – even positive saturation water.

It should be reasonable to assume that when plaster loses some of its material (such as calcium hydroxide) from the surface, this loss creates porosity in the plaster surface. Increasing porosity reduces the long-term durability of the plaster surface, since it allows greater water penetration and movement. Greater porosity also increases the likelihood, severity, and permanence of staining discolorations.

Unfortunately, there is no current pool industry standard or guideline limiting how soon water can be started to fill a new plastered swimming pool. The filling of some pools is often started before the finishing crew has even left the job site. This is an area where onBalance thinks scientifically-derived standards could improve the consumer product.

The plaster coupons used for the first phase of the study were made with a water-to-cement ratio (w/cm) of .44. This means that .44 pounds of water was used for every pound of cement. The aggregate in plaster is not counted as part of the w/cm.  A .44 ratio would be considered a low w/cm for the pool industry, and results in a beneficial and desired thick mix for plastering pools.

For the second phase of our experiment, we formed plaster coupons using a higher w/cm of .56, which results in a more watery mix. This scenario can sometimes happen if the plaster mixer person adds too much water to the mix.

We placed these newly formed plaster coupons in water at the same time intervals, or fill delays as in our first phase. The pH was tested again after 24 hours of coupons being placed into the water. As before, the pH rose in all tanks, but this time it rose even slightly higher than before. The water with the 24 hour coupon rose to a pH of 8.7, slightly higher than the pH of 8.5 recorded in the first phase. The 30 minute coupon rose to 9.5, also slightly higher than the pH of 9.2 that was recorded in the first phase.

CONCLUSION #3 – The wetter the original mix, the more plaster material is dissolved off the surface and into the pool water. This is an additional factor to the fill delay issue itself. Again, the loss of material from the plaster surface creates porosity and will shorten its life-expectancy. A high water/cement ratio decreasing a cement-based product’s durability is established, fundamental cement science.

Unfortunately, there is no current pool industry standard or guideline limiting how much water can be used in a plaster mix. This is another area where onBalance thinks scientifically-derived standards could improve the consumer product.

As a third variable in this study, the process was repeated using various amounts (1%, 2%, 3%, and 4%) of calcium chloride (for hardening acceleration which plasterers use) in the making of the plaster coupons. Testing the water for chloride just five days after the coupons were submerged in water showed that some of the calcium chloride from the plaster coupons was dissolving into the water. We learned that about 10% to 25% of all calcium chloride that was added to a plaster mix dissolved out of the plaster paste and into the swimming pool water.

The highest amount of calcium chloride loss came from the coupon with the highest w/cm and placed into water the shortest time (30 minutes). And of course, the least calcium chloride loss was from the most durable coupons – with the lower w/cm in the plaster mix and with the longer hardening time before submersion in water.

Losing yet another paste component, this time calcium chloride, from the plaster surface into the water leads to yet more porosity. In combination with calcium hydroxide loss, a significant level of additional porosity can be created in a plaster surface.

Past industry standards recommended a limit of 2% of calcium chloride (CC) in plaster mixes. Unfortunately, it appears that there is an effort by the NPC to allow greater levels as a result of (inaccurate) conclusions from the NPIRC research. This potential increase in the standard is contrary to existing cement science, and contrary to our research applying known science specifically to pool plaster.

After being in the water for 7 days, all of the plaster coupons were removed from the water tanks. Remember the plaster dust in bottom of the water tanks?  Could dissolving this dust and measuring the calcium increase from the starting point be another way of evaluating the effects of fill delay, of water-to-cement ratios, and CC additions?

Sufficient acid was added to the water tank to dissolve all of the precipitated “plaster dust” at the bottom. Then the water was tested to determine the total amount of calcium that had dissolved out of the plaster coupons and into the water.

The water that contained the coupons with the lower w/cm of .44 and the longest fill delay of 24 hours was tested. The calcium increase was 10 to 20 ppm. Since the ratio of plaster surface to water volume in this experiment was similar to that of a pool, this can be equated to about 2 to 3 pounds of calcium carbonate dissolved away from the surface of a 20,000 gallon swimming pool.

Next tested was the water that contained the plaster coupons with the higher w/cm of .56, the shortest fill delay of only 30 minutes, and 4% CC. The calcium level in these tanks increased about 180 ppm in just 7 days!  This 180 ppm of calcium increase is the equivalent of 30 pounds of calcium carbonate lost from a new plaster pool surface into the water of a 20,000 gallon swimming pool! Quite a difference!

We learned from this study that although calcium hydroxide and CC can be dissolved by balanced water, proper construction and curing practices can reduce the amount of this material that is dissolved away from the surface – resulting in a denser and better product.

The results of this pool plaster durability study indicate a need for the plastering industry to set scientific standards and limits for:

• minimum times for hardened plaster to set and dry before filling the pool with water
• maximum water-to-cement ratio
• maximum calcium chloride content
• Ensuring that tap water contains sufficient calcium and alkalinity (positive LSI) before using for filling pool. (This was actually proved by a different experiment, and the Bicarb start-up program should be recommended)

The American Concrete Institute’s Guide to Durable Concrete (201.2R-01) “describes specific types of concrete deterioration” and “contains a discussion of the mechanisms involved and the recommended requirements for individual components of concrete, quality considerations for concrete mixtures, construction procedures, and influences of the exposure environment, all important considerations to ensure concrete durability”.

This guide provides the following recommendations for obtaining abrasion resistant concrete surfaces and resistance to mild acid attacks:

• Use a low water-to-cement ratio at the surface which will reduce permeability. Tests indicated that w/cm of .40 provided significantly better protection than w/cm of .50 and .60, and a w/cm of .62 provided little protection. (A high water/cement ratio also causes shrinkage and craze cracking).
• Avoid the use of supplemental water when troweling. Do not finish concrete with standing water because this will radically reduce the compressive strength at the surface by increasing the surface water/cement ratio. (Also causes craze cracking of surface)

Other documents from the ACI and Portland Cement Association advise against using more than 2% of calcium chloride to the weight of cement due to the detrimental effects of drying shrinkage and discoloration.

All of these recommendations are consistent with the results of our study.

Identifying Curing Effects on New Pool Plaster

Newly plastered pools must be filled at the right time, and any water exposure must be even and uniform. Filling a pool too early results in a weakened and deteriorated paste surface, especially in the bowl of the pool where the effect is worse because it may be exposed to fill water mere minutes after final troweling. The optimum fill delay (time between final troweling and filling the pool) is at least six or more hours.  (Moderate temperatures and sufficient humidity is also necessary for proper hardening and curing of plaster). This fill delay is often realized for the upper half of the pool, which may not be submerged for a day or longer depending on water pressure, while some plastering crews start the fill before they leave and thus compromise the lower areas of the pool.

Wetting of parts of the surface by rinsing down the deck, rinsing off pool steps or areas where debris falls, etc. must also be avoided, since the uneven exposure of fresh plaster to water makes permanent discoloration. The fill must also be continual – pauses in the fill may result in “bathtub ring” permanent discoloration.

Identifying Plastering Defects on New Pool Plaster

Discolorations – New pool plaster can discolor (darken or turn gray) from adding excessive calcium chloride set accelerator, from late hard troweling, from thin and thick areas due to an uneven shell, etc. Gray (or grey) mottled discoloration (also known as “water entrapment ” or “hydration”) is difficult to remove, may be remedied by acid washing, sanding, or torching the surface, but these processes are generally detrimental to a plaster finish and the discoloration often returns later. Late hard troweling can cause “trowel burn” which darkens the plaster color in localized areas. Sanding can remove this discoloration.  Mottled color variation from calcium chloride or other sources may not be removable.

White Spotting and Streaking Deteriorations– Plaster may have white (lighter color) porous (soft) spots and streaks resulting from the addition of water to the hardened surface during late hard troweling in plaster containing excessive calcium chloride. This late hard troweling disturbs surface aggregate, and added water penetrates around that aggregate and spreads laterally through the porous paste caused by accelerated shrinkage. Beginning as excess porosity around the disturbed aggregate, soft spots expand and sometimes coalesce into larger affected areas. Disturbed zones along accent or surface tile, around fittings, etc. may also display this non-removable deterioration.

Whitened Discoloration of Colored Plaster – Integrally colored pool plaster may show whitening (lighter color) either uniformly or in patterns. Uniform discoloration may be caused by using incompatible admixtures: specifically color and calcium chloride. These colored plasters may also be discolored (white streaking or spotting) from the addition of water to the surface or to trowels applied to the surface during finishing. These discolorations are permanent.

Spalling – Spalling is the flaking or peeling of a thin layer (1/8 inch or less) of plaster, usually in small areas on steps and shallow end floors. It is caused by the over-troweling of the surface when the underlying paste is wet but the surface cement laitance is dry. It can also be caused by adding too much water while troweling. This usually results from improperly timed troweling, or from hot, windy or dry days. When water evaporates from the surface faster than mix water bleeding up can replace it, and then when that surface dry crust is troweled, a weakened subsurface zone is created that will be prone to spall. Spalling may occur immediately, or even years later, from surface impacts, stress from suction cleaners, or when the pool is drained, etc. Spalls may be sanded, although if a large percentage of a pool is spalled the pool may need to be replastered.

Delaminations – This is the separation of an entire new layer of plaster from its underlying substrate, whether that is old plaster, gunite or shotcrete, etc. Delaminations are usually first seen as a round surface area that has raised or pulled away from the wall, often with small cracks and nodules forming. This defect is usually caused by improper surface preparation to create a good bond with the new material.  It may manifest itself within a month or two or several years later when the pool is drained and the plaster dries out. Ground movement such as during earthquakes, can also initiate bond failure. Occasionally, some plaster areas completely pop off, exposing the underlying surface. Delaminated areas may be patched if small, but larger delaminations require replastering.

Calcium Nodules – Nodules are a form of efflorescence, or the migration of calcium salts from the plaster interior to the surface. As the calcium carbonates at surface, nodes form which may be circular volcano-type formations or stalactite-like drips down the plaster wall. They are most often associated with delaminations (as mentioned above), or with severe craze cracks, either of which allow water to penetrate the surface and dissolve and bring calcium from the interior to the exterior of the pool plaster layer. Nodules may be removed by sanding or scraping, but may recur if the delamination void or the craze network is not yet fully carbonated.

Craze Cracks – Crazing is an excessive amount of surface shrinkage cracking which can result from an overly-wet plaster mix, from excessive calcium chloride set accelerator added to the mix, from the adding of excessive water while troweling, or from excessive drying of the plaster before the pool is filled. Crazing often leads to other problems including calcium nodules, staining, and provide a home to black algae. Excessive crazing may require replastering.

Identifying Chemical Effects on New Pool Plaster

Staining – Fill water containing excessive levels of iron, copper, or other metals can cause various colors of staining, and should be filtered and removed, or at least treated before the pool is filled, or, if that is not possible,  immediately upon filling the pool to the surface tile level. This kind of staining can usually be removed by acid washing, sanding or chelation. Some of these techniques are invasive to the surface, and avoiding staining is better than removing it later.

Stains or Etching from Improper Chemical Addition – Pool chemicals need to be added to the water in a manner that prevents aggressive amounts of chemical or imbalanced water from affecting the new plaster surface. Acid should always be pre-diluted before adding, salt should only be added after 30 days of plastering, and should not be allowed to sit as a solid on fresh plaster, and cyanuric acid must also not sit as a solid on new plaster.

Water Balance, Scaling and Etching - Before filling a new plaster pool, the chemistry of the fill water should be determined. Water that is too soft (aggressive) can create plaster dust, and etch or weaken the new plaster surface, and should be balanced before filling pool. Of course, once the pool is filled, APSP water chemistry parameters and the Saturation Index provide excellent guides for maintaining pool water in a manner which will minimize detrimental effects to the new plaster surface. The LSI parameters of -0.3 to +0.5 is the acceptable limit.

Etching (from low pH/alkalinity/calcium) and scaling (from high pH/alkalinity/calcium) are uniform effects across the pool surface, unless affected by areas of greater or lesser pool plaster surface porosity. The etching process can create a rough surface, but does not discolor the plaster. Calcium scale on the surface is generally rough, white, and uniform. In time, the scale and an etched surface will attract dirt and minerals, and discolor. Although stains, dirt, and scale deposits can generally be removed by sanding, acid washing or chelation, etching is permanent and can only be moderately mitigated by sanding the surface.  

Acid Start-ups – Swimming pools should never undergo the acid start-up process. Designed as a way to remove plaster dust without filtration, acid start-ups are too aggressive for fresh plaster and will etch the surface. Subjecting fresh plaster to water with a pH below 5 is not an appropriate substitute for doing things right in the first place.

The Bottom Line

Plaster Dust in New Pools – This is the bleeding (loss) of calcium from a weak and porous plaster surface caused by improper plastering practices and/or as a result of filling too soon or with too soft water. This dust can harden into a surface calcification and trap dirt or metals, creating further discoloration. Dusting from new pool plaster is preventable by properly mixing, troweling, curing the surface with sufficient humidity and moderate temperatures, waiting at least six hours before filling, and then ensuring the chemistry of the fill water is balanced. When necessary, the fill water chemistry should be adjusted by adding sodium bicarbonate, acid, chelating or sequestering agents, etc. through a slurry tank as the pool fills. Although plaster dust can be removed by brushing and filtering, the damage from the calcium loss from the surface creates porosity and is permanent.

Prevention is the key – proper plastering procedures, proper curing, and proper water balance result in a plaster surface that is both maintainable and aesthetically pleasing. Fixing errors after-the-fact is generally less than desirable, and some detrimental effects can only be remedied by replacing the plaster.

This is written for builders, remodelers, and pool plastering contractors who are interested in providing a long-lasting and pleasingly aesthetic pool plaster finish, especially colored plaster.

Recent studies by onBalance have determined that plastering in hot and dry temperatures can have a detrimental effect to the quality and durability of the plaster surface. At issue is the fact that when a plaster surface dries out, hydration and hardening stops. This results in a plaster surface that is soft and weak and that will not be ready to withstand being submerged in water.

To demonstrate this issue, a plaster coupon (A) was formed that was then exposed to the sun all day, with temperatures reaching 90 degrees at about 30% humidity. The next morning, this coupon was placed in balanced water (actually +0.3 SI). After five days, plaster dust was visible on the bottom of the tank. The coupon was removed and the plaster dust (calcium carbonate) that developed in the water was dissolved by adding acid. The resulting calcium hardness level in the tank was determined to have increased 65 ppm.

Next, the experiment was repeated (Coupon B) when the ambient air temperature was hotter at about 100 degrees, and humidity was lower at about 20%. An additional coupon (C) was formed also, but this coupon was immediately placed in a controlled environment for 24 hours to harden, where the temperature was 75 degrees at about 35% humidity.

The next morning both coupons (B and C) were placed in separate water tanks. After five days, the water in the tank with plaster coupon B, which was exposed to the hot sun, had a calcium hardness increase of more than 120 ppm, after the plaster dust was dissolved. That is the equivalent of about 20 pounds of solid calcium carbonate being dissolved from the plaster surface of a 20,000 gallon pool.

Plaster coupon C, that hardened in the temperature- and humidity-controlled environment did not develop any visible plaster dust. The calcium hardness of the water increased a nominal 10 ppm.

In these tests, it was also determined that if calcium chloride (a hardening accelerator) is added to the plaster mix, an even higher amount of plaster dust formed in comparison to plaster samples that did not have any calcium chloride added, regardless of temperature.

When calcium is lost from a plaster surface, it causes a loss in density and an increase in the porosity of the surface. This in turn will result in a loss of durability of the plaster surface and will likely trap dirt and minerals easier, causing discoloration sooner than would otherwise occur.

Contractors should be aware that with dark colored pool plaster, an increase in the porosity will cause whitening or a lighter color developing over time as the surface loses calcium or other plaster material. This has been a sore issue for the pool industry for a long time. Of course, other improper plastering practices also contribute to this problem besides plastering in hot dry weather. Adding calcium chloride to an integrally colored plaster mix, or applying excessive water while troweling can also result in increased porosity and lightening. Improper water chemistry is often incorrectly blamed for the whitening of colored plaster, including pebble and quartz pool finishes. (Of course, whitening due to scale depositing on the plaster surface is a water chemistry issue).

Some plastering people claim that the solution to plastering in hot and dry temperatures is to immediately fill the pool with water after final troweling; that it is better if plaster is cured under water, which helps prevent the plaster from cracking in the heat. That is only partially true. Yes, the pool plaster matrix does gain added strength while curing under water, but the plaster “surface” needs to be sufficiently hardened before being submerged in water. Otherwise, the water filling the pool overwhelms the correct ratio of water to cement at the surface, which can cause a number of defects, including a general dissolution of plaster material from the surface. This has been documented. (See my prior blog post “Poor Plastering Practices vs. Aggressive Water”) Only after the surface has been properly hardened is curing under water beneficial.

In regards to cracking, good plasterers know that using a low water: cement ratio, little or no calcium chloride, and no excessive water troweling are very effective in avoiding cracking, even in hot weather.

Finally, the best solution to plastering in hot and dry weather while avoiding the detrimental effects it causes is to “tent” a pool and use an evaporative cooler to supply cool and humid air underneath the tent. This will also protect pool finishers. Tenting should be used during the entire plastering process, the six hour waiting period before filling, and until the pool is full of water.

The Portland Cement Association (PCA) and American Concrete Institute (ACI) have conducted many studies showing that cement work in hot and dry temperatures has a detrimental effect to the quality and durability of such products. They also suggest various methods to protect concrete surfaces from hot and dry temperatures. Pool plastering is a more, not a less challenging process than other cementitious applications due to the fact that pool plaster is generally troweled to a smoother finish than is concrete flatwork, as well as the thinner application, the rich mix and the need to be maintainable in the pool water and chemistry environment. Thus it is even more critical for pool finishers to follow optimal practices derived from cement science.

Although salt water has been used successfully for some time in cured plaster pools, there doesn’t seem to be much scientific documentation on the effects salt may have (detrimental or not) on plaster when it is new and still curing. There seems to be some consensus to wait 30 days before adding salt, yet some say it is okay to add salt within a couple of days of filling the pool. So who is right?

To answer that question, let’s take a look first at what happens in the initial days and weeks of a new plaster surface. When plaster is applied and a new pool is filled, the cement portion of the new, hardened pool plaster contains about 10 to 15% calcium hydroxide, the rest being primarily calcium silicates, aluminates and carbonates. These latter products are durable and relatively insoluble in water.

On the other hand, calcium hydroxide, having a pH of about 12, is softer, somewhat soluble, and can be dissolved from a plaster surface even by typical balanced tap water. Indeed, the Saturation Index that we are all familiar with as a maintenance tool to protect pool plaster (calcium carbonate) is not applicable to fresh plaster (i.e., less than a few weeks old) that still has calcium hydroxide on the surface, because the pH that would be neutral to calcium hydroxide would need to be nearly 12!

This is why the pH of the water in a freshly filled pool usually rises noticeably as soon as the pool is being filled. High pH calcium hydroxide dissolves from the plaster surface and into the water, shooting the pH up. Once the new plaster surface is carbonated (which means the calcium hydroxide is converted to calcium carbonate) this process stops.

Since dissolved calcium hydroxide also converts to calcium carbonate in the pool water, this is the source of so-called “plaster dust” in new plaster pools. When undergoing a traditional start-up process, carbonation of the surface usually lasts about 1½ to 2 weeks… which is why new plaster dust is generated for that long – and then stops. At that time the pH becomes stable in the pool, since new hydroxide is no longer being dissolved into the pool water.

The onBalance team decided to conduct an experiment in a laboratory setting to determine what effects salt may have on fresh plaster and on the curing process. The following are the details and results of our simple experiment.

On Day 1, four good quality plaster coupons were formed and allowed to harden.

On Day 2 the coupons were placed into four separate water tanks. The water in all four tanks were balanced to the same parameters; Temp = 70°F, pH = 7.6, TA = 160 ppm, CH = 200 ppm. The tanks were capped to slow down carbon dioxide out-gassing. (When water loses CO₂, the pH rises with no change in TA).

Day 3, after 24 hours in water, the pH of the water was recorded and in all four tanks the pH rose to 8.4, indicating that some hydroxide from the plaster surface had been dissolved away and into solution. (Note that this occurred even in balanced water).

Then Tanks 3 and 4 had 3000 ppm of salt added. Acid was then added to all water tanks to lower the pH to 7.6.

On Day 4, the pH in Tanks 1 and 2 rose slightly to 7.7. But in Tanks 3 and 4, the pH had risen much higher to 8.6, indicating a significant effect on the plaster surface material. Acid was added to Tanks 3 and 4 to lower the pH back to 7.6.

On Day 5, the pH in Tanks 1 and 2 was 7.8, but in Tanks 3 and 4 the pH rose to 8.4. Again, the pH raised more in the Tanks that had the salt added. Acid was added again to all Tanks and lowered to pH 7.6.

On Day 6, the pH in Tanks 1 and 2 was 7.7, but in Tanks 3 and 4 the pH was 8.2. The pH was not adjusted downward.

On Day 11, the pH in Tanks 1 and 2 was 7.8; the pH in Tanks 3 and 4 was 8.4. At this time, 3000 ppm of salt was added to Tank 2.

On Day 17, the pH of Tank 1 was 7.8; the pH of Tank 2 was 8.0, the pH of Tank 3 and 4 was still at 8.4. This data shows that the salt added to Tank 2 after 11 days had a slight effect on the plaster coupon in comparison to Tank 1. The pH is all tanks were lowered to 7.6.

On Day 21, the pH of all tanks was identical at 7.8.

The results obtained suggest that adding 3000 ppm of salt does have a negative effect on plaster if added in the beginning at startup and up through the first two or three weeks. When salt is added to water containing fresh plaster coupons, the pH of the water increased significantly higher than normal. This indicates an additional amount of calcium hydroxide is being dissolved and removed from the plaster surface. This likely causes an increase in the porosity of the plaster finish, which weakens and ages the surface prematurely.

The data also indicates that the negative effect of salt on new plaster only lasts about three weeks. As mentioned above, this is because a new plaster surface becomes carbonated; meaning that any calcium hydroxide (on the plaster surface) that is not dissolved and converted to water hardness and/or plaster dust is slowly being converted into calcium carbonate during the first three to four weeks of being filled with balanced tap water. This conversion creates a protective and more durable plaster finish. It appears that once the plaster surface has been sufficiently and properly carbonated, salt does not have the same negative effect on calcium carbonate as it does on calcium hydroxide.

Our experiment used well-made plaster coupons, which received proper curing, and positive Saturation Index water.  If, in the field, proper plastering practices are not followed closely, which results in a lower quality finish, more time may be needed before salt should be added. It appears that the recommendation to wait 30 days before adding any salt is appropriate for most plaster pools, including quartz and pebble pools.

Interestingly, the National Pool Industry Research Center (NPIRC) at Cal Poly conducted similar experiments with two salt pools during Phase 2 (2004-2005).  Unfortunately, the results were inconclusive and not supported with reliable data.

onBalance

1-15-2011

Just how much do swimming pool chemicals add to the total dissolved solids (TDS) content of the water? Do all chemicals of equal amounts (by weight) add identical amounts of TDS to swimming pool water?

When one pound of a chemical is added to 20,000 gallons of water, the usual amount of TDS being added to the water is 6 parts per million (ppm) of TDS. While this is true with most chemicals, it is not true with all chemicals. After being added, some chemicals will escape from the water and not contribute to TDS. Another possibility is that portions of some chemicals will convert into water and thus will no longer be part of TDS.

We will first look at adding a pure chemical that provides the full increase of its weight to the total dissolved solids content of the water. Chlorine gas is a good example. At levels of 1000 parts per million or below, chlorine gas is nearly 100 percent soluble at a pH of 5.0 or above. Therefore, if one pound of pure chlorine is dissolved into 20,000 gallons of water, the result will be 6 ppm of chloride (which is TDS).

One way of calculating this is as follows: 20,000 gallons of water weighs about 166,700 pounds, which is one-sixth of a million. Multiply the one pound of chlorine by six to get the 6 ppm of TDS.

As with all acidic sanitizers, after chlorine gas is added, it is usually necessary to add sodium carbonate (soda ash) or sodium bicarbonate (bicarb) to adjust the pH and alkalinity upward. Interestingly however, adding these alkaline chemicals does not ultimately add the full amount of TDS per pound added.

When soda ash and bicarb are added to pools, these chemicals will react with acid that has been added to form carbon dioxide, which, over a period of time, will release into the atmosphere. Only the sodium element from these two chemicals remains in the water and increases the TDS.

The following equations will help illustrate:
Na2CO3 + 2HCl = 2NaCl + H2CO3
H2CO3 = CO2 + H2O

In the first reaction, soda ash (Na2CO3) reacts with acid (HCl) from acidic sanitizers, muriatic acid, or dry acid, to form sodium chloride (NaCl) and carbonic acid (H2CO3). Sodium chloride remains in the water as salt, which does contribute to TDS, while carbonic acid will dissociate into carbon dioxide (CO2) and water (H2O).
The pure water that is formed does not contribute to TDS, and carbon dioxide will eventually escape into the atmosphere – thereby not contributing to the TDS content. Sodium bicarbonate also reacts with acid and forms the same compounds – salt and carbonic acid.

To determine the actual amount of TDS that is being added by these chemicals, a look at their molecular weight is needed. The (rounded off) molecular weight of soda ash is 106, and sodium bicarbonate is 84. Sodium by itself has a molecular weight of 23, and there are two sodium molecules in soda ash, only one in sodium bicarbonate. The sodium element (which adds to the TDS content) comprises about 43.4 percent of the soda ash, and about 27.4 percent of the sodium bicarbonate. Therefore, when adding one pound of soda ash, only 43.4 percent would contribute to TDS, and with sodium bicarbonate, 27.4 percent contributes to TDS.

The calculations are as follows: if one full pound of a material in 20,000 gallons of water would normally equate to 6 ppm of TDS, then one pound of soda ash, with only 43.4 percent of its total weight (sodium) remains as TDS, contributes about 2.6 ppm of TDS. Likewise, one pound of sodium bicarbonate (with 27.4 percent as sodium) adds about 1.65 ppm. (Note: Until these chemicals actually react with an acid, the entire contents of the various compounds would be present as TDS).

Another type of chemical which does not introduce the full TDS of its weight are compounds which adds hydroxide or which forms hydroxide when added to water. Hydroxide (OH) will likely combine with a hydrogen ion to form pure water (H2O) and no longer be TDS. Sodium hypochlorite (often referred to as liquid chlorine or bleach) is an example of this type of compound.

In every gallon of sodium hypochlorite (in this example, 15% trade or 12.5% by weight), there is about 1.25 pounds of chlorine and about 1.6 pounds of sodium hydroxide, for a total of 2.85 pounds of potential TDS. This would normally equate to about 17 ppm of TDS for every gallon added to a 20,000 gallon swimming pool. However, since hydroxide accounts for about 42.5 percent by weight of sodium hydroxide (and since hydroxide will eventually react with hydrogen and convert to water), this component is subtracted from the compound, so that, together with the chlorine (contained in bleach), about 2.2 pounds in a gallon of sodium hypochlorite adds to the TDS content of a solution. Thus one gallon of sodium hypochlorite adds about 13 ppm of TDS (rather than 17 ppm) in 20,000 gallons of water. (Bleach also adds a small amount of alkalinity to the water).

With 10 % (weight) bleach, about 10.5 ppm is added, and with 5.5% (weight) household bleach, about 5 ppm TDS is added, per gallon to 20,000 gallons of water.

Also, chemicals that include oxygen or nitrogen will also likely lose portion of their weight, thus a lower overall TDS contribution. Calcium hypochlorite (65%) is an example of a compound that adds oxygen. The percentage of the calcium hypochlorite contribution that ends up as oxygen is about 22 percent. Cal Hypo also contains a small amount of water. Therefore, its contribution to TDS is only about 75 percent of its total weight. Lower strength Cal Hypo will result in a slightly lower percentage of TDS contribution per pound. (Of course, part of the TDS contributed by calcium hypochlorite is calcium, which is added to the water and increases the hardness).

Trichlor, sodium dichlor, cyanuric acid, and regular salt, added to swimming pool water will result in the full increase of their weight to TDS.

Muriatic acid (hydrochloric acid) is product that, when added to pool water, will contribute significantly to the TDS content. Muriatic Acid at 31.45 percent strength adds about 3 pounds of TDS per gallon. Although the hydrogen from this acid will react with hydroxide to form water, it is such a small percentage of the total weight of the acid that it will not significantly effect the contribution of this acid to TDS. Therefore, one gallon of muriatic acid in 20,000 gallons of water will increase the TDS 18 ppm.

It is recognized that this information on TDS isn’t critical to the understanding and maintenance of water balance, but perhaps some will find it interesting.

Are you aware that the National Plasterers Council (NPC) has rejected APSP’s long-time Saturation Index (SI) standard of -0.3 to +0.5 for water balance? The NPC decreed in 2008 that pool water must be maintained within a Saturation Index (SI) range of 0.0 and +0.3. Negative index values are not allowed.

Interestingly, the NPC claims that they include other industry groups for input and consensus, yet, as far as we know, the NPC did not receive agreement from the APSP Recreational Water Quality committee (RWQ), APSP’s Technical committee, APSP’s Service Council, or pool service associations such as IPSSA and the UPA.

The NPC has also stated that they would “abide by the results obtained” from the research performed by the NPIRC at Cal Poly before policy changes are made. Yet, the NPIRC studies have not proven this new position of the NPC.

This type of thing also happened in 2003 when the NPC made changes to their Technical Manual, blaming improper water chemistry for several different plaster defects. Several pool industry members (including IPSSA) asked the NPC for supporting evidence for the Tech manual changes. The NPC did not provide any documentation.

When balancing water, is it not reasonable to allow for occasional negative indices to offset maintaining pool water with a positive SI? Is it not reasonable to allow for occasional negative indices in hard water areas of the country, or where calcium hypochlorite or bleach is used for sanitizing? Where is the proof that an occasional and slightly negative Saturation Index is detrimental to pool plaster?

In addition to their decree on the SI standard, the NPC narrowed other water balance parameters for service techs to follow. Instead of adopting APSP’s minimum and maximum values, the NPC wants to restrict all pool chemistry to only the ideal ranges – so instead of a calcium hardness standard of 150 to 1000 ppm, the NPC claims that 200 to 400 ppm of calcium hardness must be maintained. Instead of APSP’s total alkalinity standard of 60 to 180 ppm, the NPC requires that alkalinity of 80 to 120 ppm be maintained, and it must be “carbonate” alkalinity rather than “total alkalinity” as established by the APSP, making it even more restrictive. Also the pH is limited to a maximum of 7.6 instead of 7.8, and cyanuric acid is limited to 50 ppm instead of the maximum of 100 ppm.

So why has the NPC narrowed the chemistry parameters to a point where it is nearly impossible to maintain pool water within that standard, and to never allow for a negative SI? This especially coming from a trade association that stonewalls establishing standards for their own product… be it water:cement ratios, calcium chloride content, incompatible admixtures, etc. etc.

Consider this: NPC consultants are often called in to inspect a pool when a plastering job has developed some plaster problems, and the pool customer is complaining about it. The focus will likely be on water balance, and not on possible improper plastering workmanship issues.

Often, a water pool test (and also a tap water test) is performed and compared only with APSP’s National “Ideal” water balance standard as the required parameters to maintain, completely disregarding APSP’s “minimum and maximum” guidelines. If any water balance parameter is found to be outside the “Ideal” range, then consultants have been known to suggest that the “improper” water balance must have led to the plaster problem.

And in a stark contradiction, following the NPC’s official chemical startup procedure results in making new pool water aggressive (from -0.2 to -0.6 LSI according to their Start-up Card) during the first few weeks after initial fill… the most vulnerable time period for new plaster. This puts service techs in an awkward position.

More and more, it has recently come to our attention that pool plaster inspectors are (incorrectly) associating aggressive water (which, to them, means any negative SI, or any single low parameter) with plaster defects such as gray mottling discoloration, white streaking, soft spots, spalling or flaking, craze cracking, calcium nodules, delamination/bond failure, and even rebar rust stains. There are no plaster studies that support these claims. And this is not without consequence – pool owners and/or service techs are being made liable for replastering pools that the plastering company itself ruined!

Is it possible that the NPC adopted this new standard specifically to enable plaster consultants to blame “out-of-balance” water chemistry for various plaster defects, which then provides “cover” for their plastering members? Is this how the NPC “solves plaster issues?”

We appreciate the industry members who emailed us some comments and questions regarding gray (or grey) mottling discoloration in plaster swimming pools. This is written to provide further details and clarification.

Gray ghost, shadowing, hydration, and severe mottling, are terms that may be used to describe blotchy gray or dark discolorations. Sometimes, plasterers also suggest that “entrapped moisture” is a cause of discoloration.

Certainly, a dark discoloration on a cement sidewalk can look like “entrapped moisture,” and the same goes for white pool plaster. All cement products are semi-permeable, meaning that water can be absorbed into the cement matrix. But the better the quality, the less permeable it will be. When pool plaster is under water, it is always saturated with water.

However, it is also known that calcium chloride is hygroscopic, meaning that it “attracts and hangs on to” water molecules. If an excessive amount of calcium chloride is added to a batch of plaster mix, perhaps that condition can enhance a darkening of certain areas of a plaster surface. Some believe that hard troweling can “seal” the surface, not letting water escape. So, perhaps the jury is still out on this. The term “entrapped moisture” is generally not mentioned in cement literature or mentioned as a cause of discoloration.

In the case of adding calcium chloride to a plaster mix, it is known that it speeds up the hydration (hardening) of the silica compounds in cement, but retards the hydration of aluminate and iron (ferrite) compounds. This will cause a darkening color to develop. Incidentally, white cement contains a small amount of iron compounds as compared to gray cement, and may show the dark discoloration more readily. (Interestingly, there are non-chloride admixtures (accelerators) available for plasterers to use that may help avoid gray discoloration).

Trowel “burn” is another cause of extreme dark discolorations of white plaster. Usually, the plasterer removes this discoloration stain by “ragging” or “wetting” the plaster surface while troweling and before he leaves the pool.

A reason that late hard troweling causes a darkening of the color of cement is because it decreases the water-to-cement ratio of the plaster surface. A very low water-to-cement ratio almost always leaves a darker finish color. One theory on the cause of graying suggests that the development and use of non-burn trowels by pool plasterers allows for late hard troweling without the “burning” of the plaster, and thus, may occasionally help cause a gray discoloration to develop.

It is known that adding admixtures such as silica fume and fly ash can also cause a dark discoloration.

It is believed by some that a thicker coat of plaster in certain areas of the pool can result in a slightly darker color.

It is believed that filling a new plaster pool too soon or spraying down fresh plaster with water is detrimental and can result in discolorations developing.

To attempt to remedy and lighten noticeable gray discolorations, some plasterers drain the pool and allow the plaster surface to bake in the hot summer sun. Some also perform a light acid wash or chlorine bleach (wash) prior to sun-baking. But remember, in general, most acid treatments will age or etch the plaster surface prematurely.

Sometimes, “torching” (heating) the gray area with a propane torch device is performed in an attempt to remove the gray color. It is unclear whether the torching process affects the long-term durability of a plaster surface. It is known however, that the plaster surface may “pop” when heated to such high temperatures, so protective goggles should be used. Be aware that the above remedies may only be temporary as the gray discoloration may return after the pool is filled with water.

There is also normal mottling of plaster where the white plaster surface has very slight shade differences from one white area to another. Again, this slight difference still has to do with the fact that plaster is made of a mixture of water, cement, and aggregate, and is a hand-crafted product. At its best, there will still be a slight variation.

As one can see, all of the above discussions regarding dark discolorations of white plaster has to do with workmanship, additives, hydration problems, and/or curing issues, not about whether the water is aggressive or not. Typical aggressive pool water does not cause a darkening of white cement, nor does it affect the hydration rate of the various cement compounds.

Gray (or grey) mottling discoloration which occasionally occurs in plaster swimming pools may also occasionally occur on other cement flatwork, including things like driveways and sidewalks. According to the American Concrete Institute and the Portland Cement Association, adding calcium chloride and troweling concrete too late when the surface is hard are two factors that can cause graying or dark mottling of the surface.

In the first picture below of a concrete sidewalk, for example, note the gray or darkened discoloration where the concrete has been troweled to a smooth surface. This mottling may have likely been caused by late troweling to smooth the area along both sides of the edging and expansion joint.

In the second picture, note that the smooth, edge-troweled border on one side of the expansion joint in this sidewalk is gray and the edge-troweled border on the other side is not gray or discolored. It appears that the non-discolored side was troweled at the proper time, but the discolored side was not.

Let’s also understand that this two year old concrete sidewalk has been subjected to rain water, which is similar to putting distilled (very aggressive) water on the surface. Note that the rain water did not cause gray discoloration of the entire concrete sidewalk surface, nor did it remove the existing gray. On what basis do National Plasterers Council (NPC) representatives claim that slightly aggressive pool water causes gray mottling discoloration in swimming pools?

We have also received reports that NPC representatives are (incorrectly) claiming that there are no similarities between pool plaster and concrete, and therefore, concrete studies and results should be disregarded. Yet, the NPC Tech manual references ACI and PCA literature numerous times as applicable to their product. They can’t have it both ways and obviously can’t refute the facts.

Let’s discuss why concrete materials and pool plaster are similar, and how improper concrete flatwork and improper pool plastering practices are similar.

Both concrete and pool plaster are made with Type 1 Portland cement. Cement is the material that reacts with water and calcium chloride which can result in a gray or darker discoloration, and hard troweling, especially late in the sequence, also causes a darkening and mottling of the surface. While concrete contains very large aggregate, relative to pool plaster, after tamping, floating and troweling is performed, the surface usually only contains small sand particles along with cement material, which would be similar to pool plaster. Issues of improper troweling, temperatures, humidity, water-to-cement ratios, porosity and density, are similar during placement for both pool plastering and concrete flatwork, and concrete/cement authorities agree (CTL/RJ Lee). And since pool plaster is only about a half-inch thick and troweled to a very smooth finish, we contend that proper workmanship, hydration, and curing, is even more critical to the durability and aesthetic appearance of pool plaster, certainly not less.

Although service techs need to be professionally responsible for such things as scaling and etching that are chemically caused, don’t let an NPC representative fool you or intimidate you into accepting responsibility for a plaster defect.

For more detailed information on concrete discoloration, click on this link below, and go to pages 3, 4, & 5. http://www.cement.org/bookstore/download.asp?mediatypeid=1&id=454&itemid=PL861

As discussed in our previous write-up (#1), NPC representatives Greg Garrett and Randy Dukes (incorrectly) claim that improper chemistry startups or aggressive water causes gray (or grey) mottling discolorations in new white plaster swimming pools. We (onBalance) put their theory to some tests. The following is an abbreviated summary from a series of our experiments, and we thank IPSSA for their assistance and financial donations.

New plaster coupons were made. A proper .45 water-to-cement radio was used. Since calcium chloride is known to cause a darker hue of white plaster, none was added. And since late and hard troweling is known to cause the darkening and spotting of cement surfaces, no hard troweling was performed.

One plaster coupon was placed into water that had a low calcium content of 80 ppm, and a slightly aggressive SI of -0.3. After six months, no graying developed.

One coupon was placed in water with a low alkalinity of 50 ppm and a slightly aggressive SI of -0.3. After six months, no graying developed.

One coupon was placed in water that had both low calcium (80 ppm) and low alkalinity (50 ppm) and a moderate aggressive SI of -1.0. After six months, no graying.

One plaster coupon was placed in distilled water (meaning a zero calcium and a zero alkalinity), and a negative SI more than a -4.0. After six months, minor etching was noticed, but no graying.

Mr. Garrett has also cited high cyanuric acid levels as a cause of graying (NPC October 31, 2007 Newsletter). He references the Arch Study and others to support his position, yet interestingly, those studies don’t mention anything about gray mottling discoloration.

Based on Garrett’s claim, one coupon was placed in water that had 150 ppm of cyanuric acid and another one was placed in 300 ppm of cyanuric acid, each with a SI of -0.3. The water in these two tanks was also periodically (about every two weeks) treated with 10 ppm of chlorine. After six months, no graying of either coupon.

There is general agreement that acid startups don’t result in gray mottling discoloration. Additionally, service techs have noted that new plaster pools filled with balanced tap water has occasionally resulted in gray mottling. This is further evidence that water chemistry has nothing to do with this type of discoloration. And when plaster coupons were made with calcium chloride added, graying was evident.

As mentioned before, both Greg Garrett and Randy Dukes contradict their claim by recommending a “zero alkalinity (aggressive water) procedure for 7 days to remove graying discoloration, even though aggressive water is what (according to them) caused the graying in the first place. In addition, their formula of adding one gallon of acid for every 2,000 gallons of water actually results in adding 2.5 times the amount of acid needed to reduce a total alkalinity of 100 ppm to zero.

Interestingly, Randy Dukes writes in his book “Pool Surfaces Problems and Solutions” 7^th Edition 2005, that if the acid treatment doesn’t work to remove the gray, then double the dosage of acid. That is far more aggressive than doing a Zero Alkalinity process. This method, he says, “will usually drive up the calcium hardness up to scaling levels 400 ppm to 600 ppm as the graying (or “hydration” as he often calls it) disappears, so dilute the calcium hardness with fresh water before rebalancing the pool.” Is it really okay to subject the plaster to such an extreme condition that it etches that much calcium from the surface – and should one really expect this to still improve the appearance?

Yet, when it comes to maintenance chemistry, both Mr. Dukes and Mr. Garrett tell service techs that aggressive water is bad for the plaster and that it causes gray mottling discoloration. Incredible!

In summation, there is no study or documentation showing that aggressive water causes gray mottling discoloration in new white plaster pools. We challenge Mr. Garrett and Mr. Dukes to provide the documentation and science proving their claim. Until then, they should discontinue blaming “out-of-balance” water chemistry for this plaster discoloration defect. The NPC should put a stop to this unfair victimization of innocent service techs, and promote unity with the service segment of our industry.

Gray mottling discolorations occasionally occur in new white plaster swimming pools, and cause of this plaster defect is being incorrectly assigned.

Gray (also spelled “grey”) or darkened blotchy discoloration of cement flatwork is known to be caused by several improper practices, including the addition of calcium chloride to the mix (even less than 2%), late hard troweling, and sometimes a cement material issue can lead to this problem (Concrete Slab Surface Defects: Causes, Prevention, Repair Portland Cement Association 2001).

Although some discolorations are the result of metals precipitating and depositing various color residues onto the plaster surface, these are referred to as surface staining. Usually, this type of staining can be easily and safely removed from the surface by acid washing, sanding, using sequestering or chelating chemicals, or other stain removal products.

For this article, we are discussing a blotchy or streaky gray discoloration that develops during the first few months, a discoloration that is difficult to remove, and is often incorrectly termed as a “hydration problem” or “entrapped moisture.” This type of dark discoloration should not be confused with metal or mineral staining.

NPC representatives, Greg Garrett and Randy Dukes, incorrectly claim that aggressive water or improper water chemistry startups causes the graying discoloration (NPC Jan-Feb 2004 & Fall 2007 newsletter, Techlines 7^th Edition). There is no research study that supports their theory, not the Arch Study, the NPIRC studies, nor even references in the NPC Tech manual. Sadly, these incorrect claims enable pool plasterers to avoid responsibility for improper practices, and place blame on to innocent service techs or pool owners.

Interestingly, to remove gray discolorations, Mr. Garrett and Mr. Dukes suggest that service techs perform a “zero alkalinity process” (a.k.a. significantly aggressive water with a Saturation Index of -4.0). If aggressive water is used to lighten gray mottling, how is it that slightly aggressive water caused white plaster to darken and turn gray, and in a blotchy, streaky, or spotting fashion in the first place?

Acidic treatments are an undesirable and improper suggestion for the service tech or pool owner to perform on a new plaster job. While the zero alkalinity process may occasionally lighten gray discolorations, it sometimes doesn’t work, or the gray color returns soon afterwards. But the most unfortunate point is that the plaster surface WILL BE ETCHED after the zero alkalinity process is performed. Interestingly, the two NPC consultants have stated (conveniently at a different time or venue) that the worse thing you can do to a plaster surface is to maintain pool water with slightly aggressive water and etch it!

But how unfortunate for the service tech and pool owner (and convenient for the plastering consultant) if the gray discoloration isn’t removed by the acidic process; because it will become difficult proving that it wasn’t aggressive water that caused the gray discoloration in the first place. We suggest that service techs not perform a zero alkalinity process, because if performed, the service tech will probably end up “owning” that discolored plaster job, and the pool plasterer may avoid being held responsible.

Gray mottling of new plaster pools is sometimes accompanied with “white spotting” or “soft spots” (also incorrectly called “spot etching” or “etching deterioration” by the NPC). Research by independent cement laboratories have documented that white spotting and streaking is not the result of an aggressive (etched caused) condition, but is caused by improper workmanship practices and troweling techniques (such as adding lots of water while troweling) which results in localize areas of greater porosity (soft areas or spots) on the plaster surface.

Not surprisingly, Mr. Garrett and Mr. Dukes have also claimed that white spotting is caused by aggressive water. Yes, it is incredible that they claim that aggressive water causes both graying and white spots. Again, they have not produced any study that supports their position on this type of defect or discoloration. We caution service techs and pool owners not to be fooled or intimidated by these false and unproven claims, and to not accept the responsibility to attempt to remedy this plaster defect.

It would be a gesture of goodwill and unity if the NPC leadership would put a stop to this unfair victimization of innocent service techs and pool owners.

For over fifty years, most (if not all) builders, plasterers, and service techs have assumed that plaster dust (that often develops during the first two weeks after plastering) is normal, unavoidable, and acceptable. But recent research has shown that plaster dust should be and can be prevented.

Although plaster dust is normal (meaning that it is commonly seen in new plaster pools), it is not ideal (meaning that we can do better – that preventing plaster dust results in better plaster). What is plaster dust made of? It is formed from dissolved calcium from the new plaster surface. Therefore, by definition, if there is any plaster dust, there was a loss of material from the once-smooth and dense troweled plaster. And when material is lost from the surface, that surface is not as dense, smooth and durable as it once was, and as it could have remained.

Our research documents that three factors promote more plaster dust: poor plaster, filling a pool too soon, and aggressive fill water. Any one negative factor can produce plaster dust, and the more a factor is abused, or when multiple negative factors are present, the more dust is formed. This calcium loss means that the plaster is more rough (even though that may not be visible to the naked eye or by touch), more porous, and more susceptible to deterioration and staining as time passes.

We have also demonstrated through our research and through field demonstrations that strong plaster, sufficient time before filling, and appropriate fill water chemistry will prevent plaster dust formation – meaning more dense, smooth, protected pool surfaces.

In the concrete/cement industry, “dusting” of a concrete surface is known to be a sign of a weak and porous surface, and that improper workmanship practices lead to that condition. ACI and PCA literature cites high water/cement ratios, adding calcium chloride to the mix, adding water to a surface while troweling, and finishing during very hot and dry temperatures as factors leading to a weak surface, and dusting or efflorescence may result on cement flatwork.

Following that lead, through a series of recent experiments and studies, onBalance has identified certain improper practices for new pool plaster that will lead to having plaster dust develop as the pool is filling with water. The critical factors are as follows.

1. A high water/cement ratio of the plaster mix
2. Adding calcium chloride to the plaster mix
3. Adding water and working it into the plaster surface while troweling
4. Plastering in extreme temperatures (hot and dry, or very cold)
5. Starting and filling the pool with water too soon
6. Aggressive tap water (any water that has a negative Saturation Index)

Plastering Practices – when plastering, the following steps are recommended; use a low water/cement ratio, limit calcium chloride additions to 1% or less to the weight of cement, decrease or avoid calcium chloride use as ambient temperatures rise, do not trowel water back into the plaster surface, avoid overly late hard troweling, and plaster in moderate temperatures (or tent the pool).

Fill Delay – allow the plaster to harden for at least 6 hours before submerging in water. (More time may be needed for certain environmental conditions.)

Fill Water Chemistry – ensure that positive saturation water is used for filling (+0.5 is recommended with a pH under 8.2). The “Bicarb Startup” process is the ideal pre-treatment chemical startup procedure, which creates positive saturation water.

By following the above recommendations, virtually no plaster dust will result and the calcium level of the pool water won’t increase. The balancing of the pool water afterwards will be much easier, the pool filters won’t get clogged up with scale, and even dark colored plaster jobs stay dark and don’t lighten or whiten in color.

Greg Garrett and Randy Dukes, members and consultants for the NPC, suggest that when aggressive tap water is used to fill a pool; it needs to be balanced after the pool is full of water. No, that is too late; balancing of the aggressive tap water needs to be done before it is used to fill the pool. Essentially, it is being suggested that aggressive tap water doesn’t start dissolving calcium from a plaster surface until several days after the pool is filled. The fact is that by the time the pool is full of water, the original (aggressive) tap water has already changed in its composition (during filling) and may be balanced; because that is what aggressive water will do, especially in contact with new plaster. The aggressive tap water immediately dissolves calcium and alkali off of the new plaster surface (producing plaster dust) within the first 24 hours, and thus, the damage has already been done! Very little bicarb or calcium may be needed for balancing by the time the service tech shows up at poolside.

Additionally, the NPC or their consultants have blamed low calcium or aggressive water for a myriad of ills, including gray darkened and blotchy plaster, white spotting, nodules, spalling, and who knows – maybe even birth defects in pool cleaners. The fact of the matter is that aggressive water causes mild etching – which slightly roughens and may lighten the surface somewhat, but not the problems mentioned above. They are improper workmanship and material issues.

The presence of plaster dust – even though it has become accepted as “normal” – is a primary indicator of a less-than-ideal pool surface. It may have become accepted as normal, but a pool that dusts is certainly not as good as it could be. For those who prefer producing a better than normal product, who pride themselves in doing their best, following ideal practices, and eliminating plaster dust is the goal. Proper plastering, adequate fill delay, and properly prepared fill water chemistry ensure that the pool owner will have a quality and durable pool plaster finish without discolorations.

onBalance June 2010

In response to my blog “Pool Startup Chemistry for Plaster” that was previously posted on September 14, 2009, some service techs have told me that they have had favorable results performing the “acid” startup; with the pool plaster remaining smooth and the white blotchy deposit being removed on new colored plaster jobs. Yes, that can be true. There are various situations where an acid startup will appear to (and can) improve the initial aesthetic appearance of new plaster.

If the material and workmanship of a new plaster job is of high quality, if the pool isn’t filled too soon, and if the acid startup is performed properly, there is little damage done to the plaster surface. Our study on Acid Startups determined that under these conditions only about 60 ppm of calcium is removed from the surface, as opposed to less than 10 ppm when good plaster is exposed to ideal startup chemistry water. That 60 ppm loss is not enough to make a noticeable visible difference. As stated in our prior article, it required a magnification of 40X to determine that the surface had been slightly affected. To the visible eye and touch, the plaster was very smooth and not discolored. However, the undeniable loss of surface calcium and resultant porosity will have an inevitable effect months down the road, and that accelerated deterioration of surface quality will likely not even be attributed to the original startup chemistry. It is usually then (incorrectly) attributed to current water chemistry conditions.

Also, when evaluating a new plaster surface undergoing acidic treatment such as an acid startup, keep in mind that when aggressive water is dissolving some plaster material, the surface can have a silky or slimy feel to it and make it seem like the surface is smoother that it really is.

There are occasional situations when the workmanship of a plaster job was done poorly, or that the tap water was slightly aggressive. That will usually result in some cement material being removed from the plaster surface (while filling) and subsequently the formation of plaster dust all over the plaster surface. As you know, the plaster dust begins to adhere to the plaster surface. Usually the simplest way to remove it is with an Acid startup or so-called zero alkalinity treatment. If that process is performed properly, the hope is that the plaster dust will be dissolved off the surface, possibly without harming the original plaster surface. It all depends on how much acid is added.

Of course, white plaster dust sticking on the walls and floor of a dark colored plaster job is far more noticeable, and the acid treatment will seem like the best option to resolve or mitigate.

There are other variables to consider when judging the merits of an acid startup. How much acid is being added? Hopefully, it is the right amount to barely neutralize the alkalinity of the pool water, so the pH does not go below 4.5. Or is it too much, where more acid is added than is necessary? Unfortunately, the over-simplified program of adding four gallons of acid to ten thousand gallons of water is often recommended in our industry. It is important to know what the total alkalinity is of the pool water. Just two gallons of 31.5% muriatic acid will neutralize 100 ppm of alkalinity in 10,000 gallons of water. If too much acid is added, the resultant pH goes below 4.5, which is known as “mineral acidity.”

And how much time elapses before the pool water is returned to being balanced? The longer the water has a pH of 4.5, the more material is dissolved from the surface. As our study indicated, if the acid treatment is extended to 7 days, then at least 100 ppm of calcium is removed. Again, however, our experiments show that that still isn’t enough to show damage visibly (without magnification) or by touch. But it is known that the plaster surface has been compromised somewhat.

If more acid is added than needed and the process lasts longer than is needed, then more calcium or cement material is dissolved from the surface. That is not good, and as much as 150 ppm can be removed by that process. That is getting close to the point where the effect may be noticed by touch or a visual examination. That is also getting to the point where deterioration may become evident after a few months have past.

We hope that those who are inclined to perform acid startups would keep track of those pools for several years, and to compare them with pools that received the typical traditional balance water startup process.

The “Traditional” startup process only results in a loss of about 10 ppm of calcium from a 20,000 gallon pool. That is not enough to make much difference in the long term. We simply want to point out that there are questionable ways of chemically starting up plaster pools. There is also an “ideal” way to chemically start up plaster pools. Service techs from across the country tell us that the “Bicarb” startup process has worked very well for them, too, and they find that after several years have past, the plaster looks better, with less discoloration or staining, and withstands an acid wash extremely well, with easier removal of existing stains.