Years ago, pool service techs learned that aggressive water etches quality plaster surfaces uniformly - that it does not pick and choose some areas of the surface to etch, while leaving other areas untouched.

The cement/concrete industry documented that improper workmanship practices can cause cement surfaces to mottle, darken, discolor, deteriorate, streak, and spot.

Yet, in the 1980’s, when pool plastering companies began seeing white spots in some of their recently plastered pools (white and dark colored), they decided that aggressive water was responsible; rather than poor workmanship. The plasterers even invented the term “spot etching,” without any evidence that white spotting was an etching phenomenon at all.


Even after two professional cement analysis labs determined (by 2003) that improper plastering practices actually caused the weaknesses that result in porous white spots developing over time, the National Plasterers Council (NPC) refused to accept that science and decided to sponsor a study on spot etching at Cal Poly in San Luis Obispo (NPIRC).

Later, the NPC announced that the NPIRC study proved that aggressive water was the primary cause of spot etching.  But their claim is incorrect. The NPIRC’s test pool experiments proved just the opposite. Some test pools maintained with balanced water developed some white spotting and gray discoloration, and some test pools with aggressive water did not develop any white spotting or gray mottling.

If you have read onBalance’s recent (2013) articles titled “White Spotting of Pool Plaster” and “Scientific Evidence of Spotting,” you would know that four prominent cement labs and petrographers (with PhD’s) have now independently and scientifically determined that improper plastering practices cause white, soft, and porous spotting. The NPC cannot refute those findings.

Many pool industry companies (including reputable plastering companies) donated hundreds of thousands of dollars to the NPC, thinking the NPIRC study would be scientific, non-biased, and credible in finding causes and solutions to plaster problems. Unfortunately, many have been fooled by NPC’s claims. What a waste of money; and the NPC/NPIRC study didn’t even contain information on proper or improper workmanship practices.

The swimming pool industry has been duped; service techs and pool owners are being deceived, incorrectly blamed, and scammed; sometimes costing them thousands of dollars for a re-plaster, because plasterers with poor workmanship are not being held responsible.

In future posts, specific details on the actual results of NPC’s study will be provided, including how their conclusions are flawed.

Comments and questions are welcomed.


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  • In future posts, we will also discuss the NPC’s incorrect claims that “ unbalanced water chemistry” causes gray mottling discoloration, shrinkage cracks, and calcium nodules to form on plaster cracks.

    It is just ridiculous. 

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