Posted by Kim Skinner on September 14, 2009 at 9:53am
Four years ago, the National Pool Industry Research Center (NPIRC) at Cal Poly reported that they had studied the effects of three different chemical startup procedures on pool plaster. (Phase 2, October 2005). The three chemical startup procedures were;• the “Acid” startup – where enough acid was added to lower the pH to 4.5 and alkalinity to zero for three days• the “pH-Neutral” startup – where one gallon of acid was added to an 8000 gallon pool, then balanced after 3 days• and the “Traditional” startup where the water was maintained in a slightly alkaline (basic) water conditionIn published results the NPIRC claimed (after waiting eight months and using just visual observations) that the Acid and the pH Neutral startups proved superior and provided plaster with better protection against etching deterioration when compared to the Traditional startup, which was reported as resulting in significant “etching deterioration.” This begs the question: How does a balanced water startup technique such as the Traditional startup result in etching deterioration? And yet the acid startup had no etching?Is the NPIRC study accurate regarding the effects of the three different startup procedures? What really is the best way to chemically start up a new plaster pool?All three of these startup techniques were recently studied by onBalance, which also included a fourth technique known as the Bicarb startup (which involves water pre-treatment with sodium bicarbonate).Two different analyzing methods were used to determine which chemical startup provided the best effect and protection for a new plaster surface. One method was microscopy (40X Magnification) to visually examine the plaster surface. The other analysis was performed by determining the calcium increase of the water that the plaster coupons were submerged in.Well made, high quality plaster coupons were formed and placed in water after 24 hours of drying in moderate temperatures. Several coupons were each (separately) placed in water where conditions duplicated the “Bicarb” startup. The second set of coupons were placed in typical balanced water (simulating a “Traditional” startup), the third set were placed in moderately aggressive water (an LSI of –0.8, similar to the so-called “pH Neutral” startup), and the fourth set were placed in water that simulated an “Acid” startup (which equals a very aggressive –4.0 LSI). After three days, the coupons were removed and the calcium level in each water tank was tested. The Bicarb startup water had a zero to 2 ppm increase in calcium, the Traditional start water had an average calcium increase of 7 to 10 ppm, the pH Neutral (moderately aggressive) startup water had a 15 to 20 ppm calcium average increase, and the Acid (or zero alkalinity) startup process had an average calcium increase of 60 to 80 ppm. An increase in calcium (in the water) indicates a loss of calcium from the plaster, and a resultant increased porosity of the surface. This produces a weaker surface which can lead to eventual staining. These results indicated that the bicarb startup program had the least amount of calcium loss, preserving the high surface density which provides the best protection for the plaster surface.While all coupon samples were white and smooth to the touch, when 40X magnification was used to examine the plaster surface, we found that the Acid startup coupons were slightly etched, with the thin layer of cream (cement) missing, the aggregate exposed. On the other hand, the Bicarb startup coupons were very smooth, with the cement cream layer still intact and the aggregate not exposed. The other two methods fell in between the Acid and Bicarb results, with the Traditional startup coupons showing just a slight effect, and the pH Neutral startup coupons just a little more exposed aggregate than the Traditional. This microscopic examination was consistent with, and confirmed the results found by using the “calcium increase” analysis method. But understand, this observation is with a microscope; the unaided human eye cannot see the difference, and the hand cannot feel the difference.The results obtained by the onBalance study differ greatly from the results obtained by the NPIRC, and in fact, are completely opposite. It would appear that the NPIRC did not consider differences in workmanship and other variables as possible causes for the deterioration and discoloration.It is evident that the Acid startup is the most detrimental method and causes irreparable harm to a new plaster surface. While the Acid startup may dissolve plaster dust and help the surface look good for a few months, this more coarse and porous plaster surface will likely deteriorate and stain earlier and easier. The Bicarb method, on the other hand, is an improvement on the industry standard Traditional method.onBalance is a consulting group comprised of Que Hales, Doug Latta and Kim Skinner
Greg, in short, the bicarb startup process is to pre-treat the tap water to establish a pH between 7.4 and 8.2, and a "combined" total calcium and alkalinity of about 500 ppm. Example, raise tap water with a TA of 100 ppm to about 300 ppm (with bicarb) that also has a calcium tap water reading of about 200 ppm. If the tap water content of alkalinity and calcium "combined" is already at or above 500 ppm, then no bicarb startup process is necessary. Next week I will submit a new blog that will explain in greater detail the "Bicarb" startup process.
Mark, I am familiar with the kind of tap water in your area (EBMUD) that has a very low alkalinity and calcium level. For that type of water, adding bicarb and some muriatic acid will bring the pH down below 8.3 while keeping the alkalinity up, and help prevent scaling problems and plaster dust. It really does work. For pebble or quartz pools, I suggest that one should not cause porosity or roughness where the cement is at surface (exposed to the water). The smoother and denser, the better, and less likely to stain or discolor.
Charlie, if any "plaster dust" is coming off the surface after more than one month of curing under water, there is a problem that needs to be determined and identified. An acid wash is not likely to solve that problem and may make it worse.
Paul, in cold climates, the new plaster CAN and SHOULD stay dry for a longer period of time before filling with water so that it can hydrate properly and completely. You are correct to adjust the (LSI) water balance for winter time temperatures. Yes I agree, if it were easier to obtain plaster samples for analysis, then I believe proper responsibility could be assigned, resolution would come along with an improvement in quality, and the conflict would end.
thank you i found this article very interesting. would you suggest in some cases where one might pump down & acid wash a gunite pool 2 yrs after marble dusting, to help dissolve the plaster dust, which is still dusting off when rubbing ones hand over it... to instead continue to just brush off the dust and continue letting it cure...and using the correct chems, good bicarb levels etc - rather than coming in and making it look good for a few months as you mention with acid wash, giving it a surface which will in the long run deteriorate much faster having had the acid on it? i am in 2 minds what to do? having read this article i'm thinking maybe i shouldn't acid wash it next season?
You do not mention the source water chemistry. Some source water comes into the pool from some muncipalities with a pH as high as 9.4. Adding Bi Carb to such a high pH would surely cause Calcium scaling right at the start. Don't you think the start-up should be tailored to the source water conditions as well as the amount of plaster dust in the pool? What about start-ups on pebble or 3m finishes where the cream is not desired on the agregate?
You mentioned the chemistry of the "Acid", Ph-Neutral", and the "Traditional" startup methods, please describe the chemistry of the "Bicarb" startup method.
Comments
Mark, I am familiar with the kind of tap water in your area (EBMUD) that has a very low alkalinity and calcium level. For that type of water, adding bicarb and some muriatic acid will bring the pH down below 8.3 while keeping the alkalinity up, and help prevent scaling problems and plaster dust. It really does work. For pebble or quartz pools, I suggest that one should not cause porosity or roughness where the cement is at surface (exposed to the water). The smoother and denser, the better, and less likely to stain or discolor.
Charlie, if any "plaster dust" is coming off the surface after more than one month of curing under water, there is a problem that needs to be determined and identified. An acid wash is not likely to solve that problem and may make it worse.
Paul, in cold climates, the new plaster CAN and SHOULD stay dry for a longer period of time before filling with water so that it can hydrate properly and completely. You are correct to adjust the (LSI) water balance for winter time temperatures. Yes I agree, if it were easier to obtain plaster samples for analysis, then I believe proper responsibility could be assigned, resolution would come along with an improvement in quality, and the conflict would end.
Mark Johnson
Thanks,
Greg