NPC Contradictions - What's a Service Tech to do?

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?


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

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

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

4. NPC Technical Manual 7th Edition Section 6.5

5. NPC Technical Manual 7th Edition Section 6.6

6. NPC Technical Manual 7th 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 3rd Edition 1998

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

13. Greg Garrett - NPC Online Newsletter Fall 2007

14. NPC Start-up Card

15. NPC Technical Manual 7th Edition - Qualifications


E-mail me when people leave their comments –

You need to be a member of Pool Genius Network to add comments!

Join Pool Genius Network


  • (sarcasm) It's always the pool man's fault. It's not the job of the plasterer to install a good looking durable product. They are incapable of doing anything wrong. (sarcasm)
This reply was deleted.