National Plasterers Council (NPC) and their references to studies that show chemical levels related to deleterious effects to pool finishes

CaveDiver1932

Well-known member
Mar 2, 2014
48
Dallas
#1
National Plasterers Council (NPC) and their references to studies that show chemical levels related to deleterious effects to pool finishes

  1. Is there any study that shows that Cyanuric Acid (CYA) above NPC’s recommended levels cause deleterious effects to pool finishes when saturation index (SI) is in recommended range or (+/-.3) and carbonate alkalinity is kept above 70 p.p.m and total alkalinity below 130 p.p.m. ?
  2. Is the NPC recommended ranges as a result of deleterious effect studies or recommended from the IPPSA, health departments, etc?

To put bounds for this inquiry for CYA:
Using as a guide from the IPSSA Basic Training Manual 2006, pg 45 “The maximum cyanuric acid level allowed in commercial or public swimming pools by most every health department in the U.S. is 100 p.p.m. There are a few states that allow up to 150 p.p.m." The IPPSA recommendation for Residential Pools and Spas:


* Minimum 10 p.p.m.
* Ideal: 30-50 p.p.m.
* Maximum: 100 p.p.m.”
Therefore, for this discussion, MAX CYA is 150 p.p.m


In addition, any study results of effects of higher chlorine levels in relationship to maintain sanitation at higher CYA on deleterious effects?

One NPC Reference that is in public domain:
https://c.ymcdn.com/sites/npconline.../resmgr/Docs/startup-card-current-rev3_wa.pdf
Cheers
Cd
 
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,500
Tucson, AZ
#2
@onBalance is the best person to answer these types of questions. I have not looked extensively, but I know of no study that shows CYA would cause deleterious effects to a pools finish. The cyanurate component to the total alkalinity is, at most, about 1/3 [CYA] concentration. So, at 100ppm CYA, you would expect about 30ppm added to the TA. It's the carbonate alkalinity that has the greatest impact on CSI and so you would have to have high CYA (over 120ppm) and very low TA (50ppm or less) before the saturation index would become corrosive to plaster. In other words, one could be fooled into thinking their TA was ok if the CYA was high enough and not bother to do the saturation index calculation.
 

onBalance

TFP Expert
LifeTime Supporter
Jul 25, 2011
870
Utah
#4
There is no study that has shown that high CYA causes discoloration or deterioration problems to pool plaster. Of course, that applies as long as the water is CSI (or LSI) balanced. Water can still be balanced when the CYA is high by also raising the alkalinity higher.

I wrote about this topic several years ago. Please see this Thread.
High CYA Levels Do Not Stain Plaster
 

CaveDiver1932

Well-known member
Mar 2, 2014
48
Dallas
#5
Plaster problem: Arch study tackles controversial. - Free Online Library

@onBalance
Your link references an ARCH (a global biocides company providing innovative solutions to destroy or to selectively inhibit the growth of harmful microorganisms who was acquired by Lonza in 2011) study. I have only located a periodical that states the study concluded that degradation occurred with high cya when water was in balance. It does not define bounds of balance however. Is this periodical in conflict with referenced statement - “Their study did show uniform etching (degradation) of the plaster coupons due to the water being aggressive, but not from high CyA only. It appears that the alkalinity was not adjusted upward to balance the water (per the LSI) when higher CyA levels (250 ppm) were maintained which means the water was aggressive.” High CYA Levels Do Not Stain Plaster

Are these studies public? If so can they be provided?

Thanks,
Cd
 

onBalance

TFP Expert
LifeTime Supporter
Jul 25, 2011
870
Utah
#6
The ARCH study was poorly conducted, and the reporting of the data was even worse. They did not provide much information. I went directly to the director of that study and learned that they had maintained the alkalinity at 90 ppm, which they apparently (and falsely) thought the water would be balanced with the CYA at 250 ppm. As you would determine, that would have the "carbonate" alkalinity at about 10 ppm, which is very low.

Their photos did show uniform etching or degradation. But not white spotting, gray mottling discoloration, calcium nodules, and spalling, as some NPC representatives claim that aggressive water causes.

Lastly, understand at that time (2004) ARCH was starting to promote their PHMB products as being better than using trichlor.
 
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,500
Tucson, AZ
#7
At a pH of 7.4, TA 90, CH 300, CYA 250, Temp 80F (no salt or borates), the CSI would be -0.88 for that study. Water that aggressive over a long period of time would certainly etch any cementitious material.

[Edited for clarity]

By comparison, if one wanted balanced water and wanted to stay at a pH of 7.4 (often quoted as an industry target value) then one would need a TA of 180ppm in order to get a zero (balanced) CSI. That would be very difficult to maintain (low pH and high carbonate alkalinity) as the outgassing of CO2 would cause constant pH rise. This is why TFP often recommends lowering TA (more specifically, the carbonate alkalinity) and maintaining a higher pH - you get a balanced CSI and much slower pH rise.
 
Last edited:
Mar 2, 2014
48
Dallas
#8
“Lastly, understand at that time (2004) ARCH was starting to promote their PHMB products as being better than using trichlor.” Perhaps this answers the question why ARCH was negitive or perhaps biased. However it is concerning that a biocides company would not be aware of CYA and the impacts to aggressive water not to mention sanitation.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,500
Tucson, AZ
#9
“Lastly, understand at that time (2004) ARCH was starting to promote their PHMB products as being better than using trichlor.” Perhaps this answers the question why ARCH was negitive or perhaps biased. However is concerning that a biocides company would not be aware of CYA and the impacts to aggressive water not to mention sanitation.
More than likely that they cared about getting the narrative right (“stabilized chlorine products are bad for plaster pool surfaces!”) than getting the science right....