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Salt Pool Blamed for Plaster Cracking and Nodules

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When a new white quartz pool in San Diego developed numerous shrinkage cracks and very rough and sharp calcium nodules everywhere, the plasterer drained the pool and sanded it, charging the pool owner one thousand dollars for the work. The crystalline nodules began to form again soon afterwards, so the plasterer told the pool owner that a pool plastering expert and consultant would perform an inspection to determine the cause.  The plaster inspector was also a long-time National Plasterers Council (NPC) Board member, but it is not known if the pool owner was given that information. 

The inspector reported the following observations and recommendations. 

1. The many random cracks were about 1.5 inches in length and had nodules on them.

2. The pH at the time of the inspection was 7.8, TA 80, CH 600, TDS 4400, (Salt content 2800), and CYA 50 ppm, so he calculated LSI as “0.0” and in balance.  (Actually, the LSI would be about +0.3).

3. He claimed that a high TDS and low “carbonate” alkalinity (62 ppm) causes calcium to be “leached” from the plaster surface (even though the LSI was balanced). 

4. He told the pool owner to purchase a Taylor K-2005 test kit so that he (pool owner) could accurately test the pool water.

5. He recommended draining the pool, sanding the plaster surface again, filling with fresh water, not adding salt, turning off the Salt System, and then properly maintaining the pool water.  He wrote that, by reducing the salt content, TDS, and calcium, the pool surface should stay smooth.

6. The inspector stated that he “saw no improper workmanship or materials on part of the plasterer.”

After the plaster inspector report was provided, the plasterer stalled and/or refused to replaster the defective pool.  About a year later, the plasterer went out of business.  The pool owner was left with a very unsightly and rough quartz pool. 

Later, a cement lab determined that the plaster mix contained 5 percent calcium chloride, which is excessive, and that the cracking occurred immediately after finishing and before the pool was filled with water.  Excessive calcium chloride additions also contribute to calcium bleeding and the formation of nodules.

What enabled the pool inspector to render that erroneous conclusion?  Disturbingly, the NPC Technical manual contains text that can be interpreted to support the inspector’s position, and enable plasterers to avoid responsibility for defective workmanship, including plaster cracking and nodules.

Are we as an industry going to allow the NPC to blame “plaster cracking and nodules” on water chemistry?

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Comment by Richard A. Falk on June 13, 2015 at 5:31pm

It certainly does not require high salt levels for this problem to occur.  My pool started to develop calcium nodules after year 7 and this was a new pool, not a re-plaster, and is manually dosed with sodium hypochlorite where long-term salt levels hover in the 1000-1500 ppm range (I dilute with winter rains annually).

The nodules are drips on the walls and rounded rough volcanoes on the floor.  In a few areas, there is explicit delamination, one of which was large enough to clearly see the huge void.  This clearly was a poorly done plaster job but the builder is no longer in business (I think he retired) and it's way past any warranty anyway.  

Now the pool is 11 years old and still showing additional nodules though the rate of new ones was fasted during years 7 to 9 when the pH was noticeably rising the fastest as well along with some CH rise (all very consistent with calcium hydroxide getting through with most of it converting to calcium carbonate.  It's ironic that proper water balance makes the problem more visible by forming calcium carbonate, but better to protect plaster surfaces than avoid the nodule visibility since the nodules can be sanded down.

I'll plan to replaster in a few years and at that time see if I can make sure they do a better job not creating voids though I understand it will be harder to bond well since there will not be chemical bonding since only the plaster will be curing and not the gunite.

Comment by Kim Skinner on June 12, 2015 at 12:35pm
Comment by Kim Skinner on June 12, 2015 at 12:34pm

Hi Mike,

Since the cracking didn't begin more than 3 years later, it sounds like a typical bond failure (delamination) problem. Check your warranty time limit.

Go to this link on "calcium nodule" formation which better explains what caused your pool to begin cracking. 

Comment by Bruce Wettstein on June 11, 2015 at 7:14am

This may be a bit different, Mike, as 7 years has passed on your pool.  When was the last time you addressed (drained or purified) your pool water?  If calcium spots are your main issue, I would want to know what your calcium level is.  It would also be interesting to hear what you pH and TA levels are as well.  Lastly, if you are in San Diego I would (personally) like to know who you've contacted for plaster work.  I may be able to let you know if you have found a reputable plaster outfit or if you may be heading down the path of the OP.

Comment by Mike Shenk on June 10, 2015 at 6:54pm
I have this problem in my pool. What is the proper way to correct it, and how can I find a professional to do it correctly. I contacted the company that installed it originally and they want $11,600 to re plaster with "a better product". My pool is 21x47 and is almost 7 years old. It started cracking after 3 1/2 years and now is unsightly and borderline dangerous in spots from the calcium.
Comment by Kim Skinner on June 29, 2013 at 10:23am

You are absolutely right Wendy.  There is no basis for pointing the finger at salt water (or any kind of water chemistry for that matter) for causing plaster to severely crack and have calcium bleeding out.  Studies on this issue have already proven that bad plastering practices is the culprit.  

Yet, many innocent service techs and pool owners can be tricked into believing this bogus claim by so-called "experts" that the plasterers call out to get them off the hook. Maybe even the plasterer simply believes the non-sense too. Of course, it is to his benefit to do so.  

Comment by Wendy Purser on June 28, 2013 at 6:51am

Would it not be common sense that this problem would have been seen and addressed many years ago in Aquatic facilities such as SeaWorld or in beach areas where even when not on salt the salt level in pools (and many times poorly balanced) increase dramatically due to make up water and storms?  Seems like the finger always points at the new kid (although not really new) in town.  But ignorance and lack of education causes us many headaches and ruins reputations for those that know based on those that think they know.

Comment by Bruce Wettstein on May 14, 2013 at 7:32pm

"As far as I know, the plasterer in question was licensed and well established in San Diego, but went out of business when the economy went south.  But you may be right that he was known for doing poor quality work".

Licensed and well established does not necessarily equate to quality, unfortunately for our industry (and many others, I am sure).  I can think of two such plaster outfits who are no longer in San Diego that exhibited those "qualities" and yet did not deserve to be in business.

Tenting and addition of CC (or not adding) are both great ideas.  As with most things, moderation is the key.

I tend to agree with you here; looks like plenty of blame to go around.

Comment by Kim Skinner on May 14, 2013 at 8:23am

Bruce, the pool was plastered in March, but don't know what the temperature was.

I am in agreement with many of your comments, however, if plasterers are concerned about warm temperatures causing shrink cracking.  Then they can "tent" the pool, not add calcium chloride (CC), and keep the plaster mix thick (low water/cement ratio). 

As far as limiting the amount of CC to 2% by the NPC, the NPC Technical Manual also states that, "the suggested 2% limit may not be problematic to swimming pool plaster."  And an NPC inspector has been known to cite that reference and text in defense of adding more than 2% on a problem plaster job.

Furthermore, there are situations and conditions that warrant not adding even 1% CC because of potential problems, especially dark colored plaster. 

There is plenty of shame to go around.

As far as I know, the plasterer in question was licensed and well established in San Diego, but went out of business when the economy went south.  But you may be right that he was known for doing poor quality work.

Comment by Bruce Wettstein on May 14, 2013 at 7:41am

I would have to say that from the numbers posted I do not see an aggressive condition either.  The pH is higher than I like to see (and not aggressive), the TA is good and the salt ppm is on the low side.  I understand that this is the "current" water condition, but still does not indicate aggressive water.

I still have a question or two:  What time of year and what was the temperature the day of plaster?  I think we all agree that the warmer the day, the better the chance of plaster shrink cracking.  It would also be nice to know how the pH was maintained (I know that is tough, if not impossible) initially, just to have some insight on where the aggressiveness came from.  Lastly, it does appear that quartz finishes tend to check crack more, possibly due to the "fineness" of the material. 

If I was a betting man, I would take a stab at who this contractor was (and I'm pretty sure I would be right!).  There will always be those in the industry that try to cut corners and choose their personal gain over quality and workmanship.  This "underground economy" that we are experiencing is also to blame, as the faster a cash guy gets in and gets out the more money in his pocket.  Shame on those clients/customers/homeowners that choose these guys over reputable tradesmen. 

5% CC is unacceptable by any measure.  I am aware that the NPC states no more than 2%, so this plaster company far exceeded the maximum allowable percentage.  Shame on him for starting out on the wrong foot, as well as for charging the homeowner for a polish on shoddy work.  I say that such companies do not belong in business in the first place. 

Interesting post.  It appears to be a chain of events that started with a poor quality plaster outfit, installing a poor product and then degrading from there.  My thinking is that this pool finish was destined to fail from the start.  Sad.

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