Being Blamed for Plaster Discolorations? Don't Get Hoodwinked


TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
Some newly plastered pools (including quartz and pebble finishes) may develop either color fading, white soft spotting (also incorrectly called "spot etching" by some plasterers), white streaking (in colored plaster), calcium nodules, gray mottling discoloration (of white plaster), spalling (flaking), or severe craze (check) cracking within a few months after being plastered, and whoever has been maintaining the water is often incorrectly blamed for those plaster problems and defects.

Generally, it will be claimed that the pool water has been “aggressive” or "scaling" at some point in time, and even if the water has never been out of balance. But more importantly, aggressive water or scaling water does not cause the above plaster problems, and cement and plaster studies have actually determined that improper workmanship practices lead to those problems developing in pools and on concrete (cement sidewalk) surfaces.

So why are these unfair accusations happening? One main reason is because the National Plasterers Council (NPC) doesn’t do anything to stop it, and in some ways, enables it to happen.

Let’s examine this issue. The NPC and some plaster inspectors define “balanced” pool water within very narrow parameters and limits, but without any supporting science to back it up. The NPC states that water parameters (pH, TA, CH) must be maintained within industry “Ideal” ranges to be considered balanced, and disregard the “minimum and maximum” standards.

For example, NPC literature essentially suggests that pool water with an alkalinity of 70 ppm is considered to be out of balance and aggressive, even if the other water parameters make the CSI balanced, the NPC still considers that water “aggressive” and able to cause plaster problems.

Rain is about 1,000 times more aggressive than an CSI of -0.1, which the NPC says is unacceptable and aggressive. Yet, when it rains for a few days, cement sidewalks don't result in white soft spotting ("spot etching" which some plasterers call it), graying, or calcium nodules. Cement sidewalks and pool plaster are similar because both contain a significant amount of Portland cement which is what discolors.

So if the water chemistry is being blamed as causing one of the above plaster problems, and a NPC inspector or plasterer gives you a copy of the NPC Technical Manual, or a report by Arch Chemical or Cal Poly (NPIRC), or APSP and other literature, and suggests that it proves whatever it is they are claiming; don’t be hoodwinked or intimidated. Those reports don’t prove that out-of-balanced water causes those problems. In fact, they mostly indicate it is poor workmanship.

Today, some plasterers (sadly) advertise that plaster only lasts 5 to 10 years. But not long ago, plaster used to be promoted as lasting 20 years. In reality, it still can and does last 20 years when quality workmanship is performed. It’s not difficult to figure out who benefits and who is harmed when plaster finishes don’t last very long.

It is unfortunate that poor quality plasterers are being helped to avoid being held responsible for bad plastering work and results. That needs to change for the betterment of the swimming pool industry.

See these threads: White Spotting of New Plaster Pools
How White Pool Plaster Turns Blotchy
How White Pool Plaster Can Turn Gray
Calcium Nodules in pools
High CYA Levels Do Not Stain Plaster
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TFP Expert
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May 23, 2015
Tucson, AZ
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Salt Water Generator
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Pentair Intellichlor IC-60
Thanks onBalance, great post! I have some mottling in my PebbleTec finish as well as two very faint brown streaks (stains) caused the worker who wasn't careful with the final acid etch step after the ptec was applied. He must have hit some of the rocks in the waterfall with his pressure spray and the resulting etching of the boulders dribbled down the side. It doesn't really bother me so I just prefer to leave it (kind of like a "birthmark").

I believe you posted a nice thread on some tests you performed on water balance and plaster coupons (I'd have to go searching for it to link and can't right now). But I believe some of those results showed that it was only extraordinarily out of balance water that really caused problems.

It is sad that the plastering industry seems to ignore sound science and data over protecting its membership from obvious workmanship issues.



Two great links -

is the Saturation Index always Reliable?

Research Reveals Need for Pool Plastering Standards


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TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
Thanks Matt. Appreciate your comments.

Yes, it does take significantly aggressive water to affect quality pool plaster in a short period of time. And the effects are readily apparent and identifiable; most often either uniform etching or uniform scaling.

It is really only a few individuals within the plastering industry that came up with the bogus concept (about 20 years ago) that aggressive water chemistry caused various plaster defects and discolorations, and many plasterers believe them. Today, they they continue to mislead and influence others. They are entrenched, and ignore or refuse to accept reality and the science that they are wrong. That is the sad reality of what is going on.
May 12, 2013
I admire what you guys are doing with this issue. It's so rare to see a non governmental agency taking it upon themselves to fight the good fight in industry on behalf of the consumer. Thank you very much.

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