For years pool industry professionals have argued over the cause of plaster deterioration: did chemicals cause etching and cracking or was it something about the plaster or how it was applied? Or did all of this contribute to the problem? In an effort to find solutions to pool surface related issues through scientific research, in 2003 the National Plasterers Council helped form the National Pool Industry Research Center (NPIRC), which consists of 12 pools and four spas, at the California Polytechnic State University (Cal Poly) in San Luis Obispo. After a few years of running protocols, the researchers at Cal Poly certainly haven't answered every possible question surrounding this issue, but they do believe they've answered a major one, and have generated many more.
Aggressive Is Bad
After their initial round of protocols conducted in 2003-2004, the researchers at Cal Poly, along with industry members from the National Plasterers Council (NPC), the Independent Pool and Spa Service Association (IPSSA) and the United Pool Association (UPA), who also evaluate the tests pools, concluded that aggressive water chemistry appeared to be the primary factor leading to the deterioration of plaster.
In the 2004-2005 protocols, pools with aggressive and balanced water were compared again, and again the aggressive pools showed signs of greater deterioration. In these comparisons, all other variables, including what sanitizer and start-up procedure were used, were the same, says Damian Kachlakev, Ph.D., the director of NPIRC and an associate professor of civil engineering at Cal Poly. "This part of the study revealed beyond any reasonable doubt that when all other conditions are the same, the water chemistry has the most profound effect on the etching deterioration of pool plaster," says Kachlakev.
But haven't we known this for years? "Yes," says John Puetz, vice president of research and development at chemical manufacturer Advantis Technologies, "but it has never been demonstrated in what you call the scientific court, where you have a direct comparison between one set of conditions and another. Is it in fact confirming something everyone assumed to be critically obvious. I think the answer is clearly yes."
David Rouse, manager of technical services at BioLab, which supplies pool and spa chemicals to the industry, points out that keeping water balanced is critical not only for maintaining plaster surfaces, but also for vinyl and for pool equipment, especially heaters. "You certainly wouldn't want to have aggressive water because you could corrode the metal components in the heater, and you wouldn't want scaling conditions to where you would scale the heating element and then it wouldn't heat properly anymore."
Is There A Better Killer.In 2004-2005, the researchers also took a closer look at various sanitizers to see if they had differing effects on pool plaster. They studied the most commonly used sanitizers today: trichloroisocyanuric acid (trichlor), sodium dichloroisocyanuric (dichlor), sodium hypochlorite (liquid bleach), sodium chlorine (salt system) and calcium hypochlorite (cal hypo).
According to the NPIRC report: "The effect of the various disinfectants was evaluated after approximately 10 months of exposure by separate assessment of etching deterioration, craze cracking and discoloration levels. The results strongly suggested that pools sanitized with a salt system developed the highest level of etching deterioration, highlighted cracking and discoloration. On the other extreme, pools treated with dichlor and cal hypo showed very minimal etching deterioration, remained almost crack-free, and revealed negligible discoloration. The trichlor-treated pools performed somewhere in the middle, but developed much less etching compared to the salt-sanitized pools."
But note the report also states: "The chlorine concentration in pools 1 and 5 could not be maintained very well due to the fact that these two salt-system pools were maintained at a salt concentration of a minimum of 3,200 ppm and this produces a very large amount of chlorine even at the lowest efficiency of the salt generators. The salt generators are designed for pools with larger capacities than the test pool volumes of 7,900 gallons."
Rouse says this leads him to believe the effect of the salt system on the plaster is undetermined, "because they haven't done a study on the aggressiveness of chlorine and that could be what was leading to the cause of the plaster deterioration. I definitely think that while they found a piece of information that's interesting, they can now set up another experiment that can give them more clarity around those findings."
Puetz had similar thoughts about the salt system results. "This is extremely interesting," he says, "but it's going to require a little more investigation as to exactly what's going on. For example, is it the salt content in the water that's at issue. Or is it because there is a device within the unit that somehow has an effect?
"This is a potential smoking gun, but why? Is it something that could actually be dealt with. Maybe it's nothing more than the need to make some minor adjustment to the water chemistry in order to offset that. I don't know what the responsible agent is. We do know it happened in a salt pool, but we don't know what it is that brought that about.
"Keep in mind," adds Puetz, "if it's simply the presence of salt in the water, salt is a normal byproduct of chlorination. In this test they were treating it with salt somewhere around 3,200 ppm, but it's very possible that after several years of use a standard plaster pool would have let's say 1,000 ppm of sodium chloride in the water as a byproduct of chlorine, so is that a potential problem for us? So it isn't just a matter of: Is it that level? It goes beyond generators. Is it salt alone and if it is, we have to be concerned, because it too will accumulate. So there are things to be looked at, no question. And that's the wonderful, beautiful thing about research — it always raises new questions."
Kachlakev notes that the NPIRC is planning on studying the salt systems further in future protocols.
Examining The Stats
While the researchers at the NPIRC made every attempt to isolate particular variables in the studies, Rouse is concerned about the significance of some of the results, "because in a swimming pool environment, you have many, many variables." He believes "it's too early for them to draw any real statistically significant conclusions because there were so many variables they were trying to test that in order to get a statistically significant result, they'd have to eliminate the amount of variables and then conduct a study where you have a larger set of populations. For instance, calcium hypochlorite they say was the least aggressive, but they only had one pool that had calcium hypochlorite, so there's only one opportunity to make your judgment off of whether it was good or bad. If you determine the result of something based off one experience, then you may not have your true answer."
Though he does have these concerns about the study, Rouse stresses that he and BioLab support the efforts of the researchers. "It's a breath of fresh air that they're conducting the studies. Ultimately, we all want the consumer and pool users to have a good experience," he says.
Start-Up Procedures
Just as they did with the sanitizers, a team of 10, comprising industry professionals from IPPSA, NPC and UPA, as well as NPIRC researchers, examined the effects of the three most common start-up procedures on plaster during the 2004-2005 protocols.
Since start-up procedures can vary a bit, following is a description of how they were done at the NPIRC. According to Jana Auringer, a pool consultant known as The Pool Lady, and a member of the NPC board of directors and the NPIRC advisory board, "At the research center, with the traditional start-up, the pools were brushed as soon as they were filled and then acid was added approximately 1 pound at a time until a pH of 7.6 was achieved. With the acid start-up, we basically zeroed out the total alkalinity and on those we added 1 gallon of acid per 2,500 gallons of water and the equipment was not turned on for three to four days, but the pool was brushed twice a day. For the pH-neutral startup, we added 1 gallon of acid per 5,000 to 6,000 gallons of water and then the water was circulated through the pool equipment. We were brushing the pool as the acid was added to the water and the pool was circulating."
Auringer adds that in general, "All this varies based on what the starting pH is, especially on a pH-neutral start-up. It would have to be based on what the pH was when they tested it prior to start-up. And testing the water prior to start-up is something many builders don't do, but should. You need to know what you're dealing with before you start dumping chemicals in it."
In terms of the test pools used to study the three different start-up procedures, they were all sanitized with trichlor and maintained as balanced. In addition, according to the NPIRC report, "Plaster mixes, maintenance techniques and application processes in all pools were practically identical."
So how did the various procedures perform at the NPIRC. The report says: "The pH-neutral start-up resulted in the least observed etching, while the traditional start-up created the most etching deterioration. The acid start-up procedure implemented proved superior to the traditional start-up, effectively reducing the observed developed etching. The study concluded the type of start-up procedure does not have any significant effect on the visual discoloration or highlighted crazing."
Although Auringer doesn't dispute the findings, she would like to look at start-up procedures more specifically in future protocols. "What was done before was really a compilation of results after the 10 month period, which also included sanitizers, so I would really like to see just an analysis of the plaster after 30 days on each type of start-up to see the difference in the condition of the plaster after that period of time to see if one type of start-up is superior over another. I think it would be more conclusive if we inspected the pools after 30 days."
Super Surface
Ultimately, Kachlakev says, the NPIRC seeks to improve pool surfaces so they can better withstand the tough pool environment. "What we're doing right now and probably will try to do in the next few years is to show there are two possible ways to solve the durability issues. One of them is to meticulously maintain the water chemistry, which is not possible. It's not that it's not practical, it's not possible. If you have a rain just for a few hours, everything changes. If your pool is on a hillside and you have some dirt blown, everything changes in a second. Perfect maintenance of the water is simply not possible. Even if it's automated, it's still not possible to maintain to such a precision; so the way to deal with this in the future is to have more-resistant surfaces, and this is what we're focusing on now. Can we modify, can we somehow create a superior surface, which will be able to withstand some aggressiveness from the water, which always is going to be there. I'm not suggesting by far that you maintain pool water as aggressive, but if the water chemistry is maintained as it is in many residential pools (i.e., checked once or twice a week), and if you have a surface that is more durable, we believe this the long-term solution."
Keep Cyanuric Acid In Range
During the 2004-2005 protocols, the researchers at the National Pool Industry Research Center at California Polytechnic State University (Cal Poly) in San Luis Obispo also looked at the effect of cyanuric acid on pool plaster and found that if kept within 40 to 60 ppm, the effect of the acid on the plaster is negligible. Unfortunately, not all residential pools are maintained at this level. "Currently, the recommendations from APSP are the ideal of 30 to 50 ppm of cyanuric acid, with a maximum of 150 and a minimum of 10," says Ellen Meyer, technology manager at Arch Chemicals. "But we have found, certainly for residential pools, a lot of pools with cyanuric acid concentrations in excess of 200 ppm.
"The reason you don't want to let it get over 150 ppm is because it does hinder the efficacy of the chlorine," continues Meyer. "There have been studies of bacteria kill rates at high cyanuric acid concentrations, and you can see that the higher the level of cyanuric acid, the less effective the chlorine is going to be." But that's not the only problem with a high concentration of cyanuric acid — it may also lead to plaster deterioration. Arch has studied the effects of cyanuric acid on plaster and found that, even in pools with balanced water, high cyanuric acid concentrations can degrade plaster.
After initially studying the effect of cyanuric acid on small pieces of plaster, called coupons, in a lab beaker and then in a test tank for six months and finding degradation of plaster at increasing levels of cyanuric acid, Arch then initiated tests in pools in May 2005. The water in the pools was maintained at a pH of 7.2 to 7.6, alkalinity of 80 to 120 ppm, calcium hardness of 180 to 250 ppm and available chlorine at 1 to 4 ppm. Also note, says Meyer, "The plaster coupons in our study were suspended vertically in the water so that nothing would settle onto the surface." If the plaster coupons were at the bottom of the pool, the cyanuric acid, which would simply fall onto the coupons, could definitely cause some etching of the plaster, adds Meyer.After four months of operation, the pictures below show the coupon from the pool with 0 ppm of cyanuric acid and surface degradation on the plaster coupon in the high (200-250 ppm) cyanuric acid pool.
Damian Kachlakev, Ph.D., the director of the NPIRC and an associate professor of civil engineering at Cal Poly, says the NPIRC does plan to study the effects of high concentrations of cyanuric acid on plaster in future protocols.
Do keep in mind, though, that cyanuric acid is still a recommended stabilizer that anyone with an outdoor pool will want to use. Now there's just another reason to keep it within the prescribed levels.
—K .E.
