It happens all over the country, nearly every day.

John Homeowner goes into his backyard to take a morning swim and finds that groups of small white spots have appeared on the surface of his pool, possibly with darker areas surrounding them. The marks could have formed gradually and gone undetected until now. Or it could have happened within weeks after the pool’s initial start-up. Mr. Homeowner calls the pool builder, and that’s when things start to get ugly.

Depending on one’s philosophy, these marks are called spot etching, etching deterioration or just spots. The marks cannot be acid washed away and often require replastering, at a cost of a few thousand dollars.

So who’s responsible? The answer to that question depends on whom you ask. Frequently, plastering firms and service firms and/or the homeowner get into finger-pointing arguments over who should cover the repairs. Nobody’s happy, including the pool builder, who generally doesn’t want to get in the middle.

Worse yet, the problem leaves homeowners with a bad taste in their mouths as they see the industry battling over an issue that’s been going on for decades. At the center of the struggle are two organizations: the National Plasterers Council and onBalance. Both represent professionals who feel the threat of lawsuits, with some even filed on the class action level. Both groups maintain that their research holds the key to the problem’s origins.

The argument recently surfaced again, when NPC issued a public challenge to onBalance, saying it would like to get to the heart of the matter once and for all. OnBalance countered by offering up its own proposal that specifies a completely different method. Each proposal drew the ire of those who sympathized with the other party; each also serves as an indicator of the different type of science and methodology upon which each organization bases its position.

Here, Pool & Spa News examines the tension between NPC and onBalance, and looks at the science presented by both groups.

The gist

The disagreement starts at the most basic level, since the two organizations don’t even see eye to eye on what spot etching actually is, though both consider the term to be a misnomer.

OnBalance refers to the phenomenon simply as “white spots,” “soft spots” or “porous spots” and says it is separate from actual etching. The group claims that the spots are caused when certain forms of calcium in the plaster mix — namely, hydroxide and chloride — are dissolved, while calcium carbonate and calcium silicates remain. This leaves areas of the pool’s surface porous, weak and soft.

Water is allowed entry into these spots by “micro cracks” and other fissures, officials say. Some of these cracks are caused when pieces of aggregate at the surface are jostled out of place during plastering if the material is troweled after it has started to set a bit.

The cause of the problem, onBalance believes, is poor workmanship on the part of plaster applicators, when they add too much calcium chloride to speed the set-up and/or splash water onto the material during troweling to make it more workable.

“A very slight amount of water used to ‘lubricate’ the trowel is not necessarily a problem,” says Kim Skinner, a partner in onBalance. “It is the excessive amount of water and re-troweling that leads to white spotting.”

The whiteness of the spots is caused by porosity, the group maintains, which extends too deeply into the plaster matrix to be sanded or acid washed away. This has been observed by scientists with the use of certain analytical tools, they maintain.

The organization disagrees with NPC’s contention that aggressive water is the culprit. If it were, Skinner says, the problem would be seen consistently throughout the pool, rather than just in certain areas. It also would not be porous, soft or white.

For its part, NPC believes spot etching is not a distinct phenomenon unto itself, but rather a subset or phase of etching deterioration, which both groups agree occurs when corrosive water pulls away at the calcium in the plaster mix, leaving a rough surface.

The spotted appearance is partly explained by the nature of cementitious materials, NPC officials say. It is impossible to create a 100-percent consistent plaster mix, and etching will first occur in spots where aggressive water comes into contact with areas where the plaster is weakest. “It’s not uniform — in other words, every square inch of that surface is not the same,” says Greg Garrett, NPC’s technical advisor.

“You’ve got different concentrations of different calcium-based compounds. Some aggregates are closer to the surface while some are further down within the matrix. So you’re always going to have these differences in plaster. You could only have uniform etching if the surface were uniform, and it’s not.”

If the water condition is aggressive enough for too long, the group says, the etching eventually could become uniform as the surface continues to be attacked. But that rarely happens, Garret says.

Spot etching began to increase in the late 1960s and 1970s. NPC attributes this in part to the increased cyanuric contents that came with the introduction of stabilizers in chlorine, resulting in more acidic sanitizers.

“In the old days, the primary sanitizers were liquid chlorine and then calcium hypochlorite. Those were very base,” Garrett says. “In the mid-’60s, when they introduced trichlor and sodium dichlor to the industry, that was really when I think things begin to change.”

This can be seen, NPC officials say, in cases when spotting occurs near areas that are exposed to newly chemically treated water where the concentration is highest, such as outlet returns. This also serves as an indicator that spot etching can be caused by chemistry, they say.

As further evidence of the link between aggressive chemistry and spotting, NPC members point to instances in Arizona and Southern California, when tap water experienced a severe reduction in calcium levels, resulting in aggressive water. Those areas saw an accompanying increase in the appearance of spots and other manifestations of etching deterioration even in older pools, officials say.

Neither side faults the plaster itself. If that were the source, both say, the problem would be more consistent and widespread.

Head to head

Both sides agree on many of the basics of what constitutes good and bad practices.

There is no question that aggressive water is problematic, so both parties discourage it. They also agree that there’s a limit to the amount of calcium chloride that should be added to a plaster mix to accelerate the set-up, as well as the quantity of water to make it more workable. But they don’t see eye to eye on what that limit is or how harmful it can be.

In terms of positioning, the NPC has a distinct advantage because the group is larger and its benchmark research was completed with donated funds, time and brainpower from various segments of the industry. In addition, as a trade group, NPC is integrated into the industry’s organizational fabric. This leaves onBalance, a research and consulting firm of three partners, feeling marginalized and not taken seriously. That said, NPC stands as a bigger target, which members feel acutely when onBalance sends emails and posts blogs criticizing the group or its science.

The decades-long conflict between the two surfaced in a public forum last November, at a meeting of the Association of Pool & Spa Professionals’ Builders Council. At the gathering, Skinner argued against some language in the APSP Builders Manual that included the NPC Technical Manual as a reference. He stated that APSP tacitly endorsed NPC’s document, and he took issue with the fact that the NPC manual had been updated since its mention in APSP’s document. Skinner said that by continuing to endorse NPC’s Technical Manual, APSP was placing itself at risk for lawsuits when spotting and other plaster issues occur.

The request to remove the reference angered some of the Builders Council members who also belong to the NPC. The discussion quickly became personal, with Skinner accused of making his living attacking the NPC, while he said that the plastering organization knowingly promotes harmful practices.

In an attempt to figure out the situation once and for all, the Builders Council proposed that NPC and onBalance collaborate on a study but, while the possibility looked promising for a while, the two groups could not agree to the terms.

Since then, the conflict has continued to flare. Earlier this year, Skinner published a commentary in the United Pool Association’s newsletter accusing the NPC of skewing the results of its studies. He said the organization expelled a member from its planning committees who didn’t agree with it, and named one specific professional who allegedly was asked to leave.

In response, Alan Smith, chairman of those committees, published his version of events. He said no committee member was ever kicked off, and that the professional Skinner named actually was a guest at a meeting and was not asked to leave.

Most recently, the dueling proposals were offered up, each adhering to the methodology historically used by its author.

On Sept. 12, NPC issued the first challenge through the trade press, proposing that test pools be plastered using onBalance-advocated methods and then studied to see if spots develop. A total of six pools would be tested - three finished in white plaster, three in colored. While onBalance would coordinate and oversee the application and pool start-up, NPC would set the ongoing chemical parameters, with maintenance performed by a member of the Independent Pool and Spa Association.

The logic behind the proposed study said that if spotting truly is caused by troweling and mixing techniques deemed improper by onBalance, then it stands to reason that the problem will not occur if the practices touted by onBalance are implemented.

OnBalance didn’t reject the study outright, but proposed an alternative. Rather than studies, it wanted to conduct a months-long, structured debate in which each organization would present detailed rebuttals of the other’s studies and research, pertaining not only to spot etching but all points of contention. A first round would involve written arguments to be submitted by the end of the year. A second phase would take the form of a face-to-face debate moderated by a pool and spa professional who has the appropriate technical acumen, but is neither a plasterer nor a service technician.

From onBalance’s perspective, enough pool studies have been performed and they’ve only served to reinforce its position, not NPC’s. Additionally, the members said, NPC’s proposal addressed etching, which onBalance believes is different from the spots. What hasn’t happened, onBalance said, is fair consideration by NPC of its position and the science behind it.

But NPC said plenty of debate has taken place in committees, the trade press, and onBalance’s emails and blog postings. In NPC’s opinion, onBalance hasn’t put the application principles it espouses to the test.

So not only were both proposals dismissed, but so were the very premises behind them.

The ongoing conflict leaves many industry professionals at a loss. Although they have a solid grasp of the science involved in spot etching, its intricacies are complex and both sides can eloquently explain their beliefs and cite credible-sounding research. Add the messy layer of a personal grudge match, and many builders prefer not to get involved. “I’m not picking sides,” says one pool contractor. “I’m trying not to even be part of it because it’s not my area of expertise.”

The future

Neither organization sees an end to this disagreement and both name incidents in which they have offered to sit down with the other and were refused.

Industry observers don’t see a light at the end of the tunnel, either. In the hopes of bringing about some level of industry consensus, officials with APSP have agreed to work with the NPC to develop an ANSI-approved plaster standard. The language will be created through a consensus process, whereby individuals from all areas of the industry have the opportunity to comment and provide input.

“Everybody feels it’s gone on too long,” says Carvin DiGiovanni, APSP’s senior director, technical and standards. “Let’s try to bring some resolution to it. If we could work together, ultimately bringing onBalance together with the NPC to find some resolution, that would be the ideal situation.”

Both sides eloquently explain their beliefs and cite credible-sounding research. Add the messy layer of a personal grudge match, and many prefer not to get involved.

The science

In addition to their own experience and observations in their general fields and as expert witnesses and consultants, both sides refer to studies and analyses to support their positions.

NPC’s research

NPC officials cite research dating back to the 1980s, including the E. Dow Whitney study performed by a professor of that name at the University of Florida.

But the cornerstone of NPC’s position is derived from research performed at the National Pool Industry Research Center at California Polytechnic State University, San Luis Obispo from 2004 to 2008.

The studies examined the effects of aggressive water on plaster, as well as how the material held up when certain additives and number of trowel passes were employed. The facility was built with 12 pools and four spas. The pools often were divided into sections that received different plaster applications, to see how each would perform under the same water conditions.

The protocol for the studies were developed by professionals from all segments of the industry, including manufacturers, engineers, service technicians, builders and plasterers, as well as Cal Poly faculty, according to NPC officials. Pool and spa professionals also built the vessels and applied the plaster. However, the studies themselves were conducted by Cal Poly staff and faculty, which also maintained and monitored the water.

In one of the first studies, published in 2005, two pools and two spas were plastered in the same manner, with one of each having balanced water, and the other two vessels containing aggressive water. The pools with aggressive water showed significantly more etching than the others, with some spotting visible. Both spas developed noticeable etching over time, though the one with aggressive water etched faster, which NPIRC attributed to the high temperatures.

The study also examined the effects of adding supplemental water during application to make the system more pliable. Less etching deterioration was observed in the areas with supplemental water. The report writer theorized that the supplemental water promoted hydration, which helped make the top layer of the plaster more dense and, therefore, more durable.

The study also compared sections with various amounts of calcium chloride added, and it was found that etching levels didn’t change among the samples with different levels. The study concluded that as calcium chloride goes up, porosity goes down in standard plaster mixes. In modified mixes, where certain admixtures such as pozzolans were added, porosity seemed to go up as a result of calcium chloride.

However, the report also stated that this was only true to a point. If calcium chloride accounts for more than 5 percent of the mix, then the material’s compressive strength, considered the primary determinant in its ability to resist deterioration, may decrease.

NPC states that calcium carbonate should never comprise more than 2 percent of the total mix.

A later NPIRC report also discussed long-term observations of two pools and a spa over the course of two years. It noted that one of the pools, whose water was chemically aggressive, showed etching that originally appeared spotted, but then, a year later, covered approximately 90 percent of the pool. A spa with aggressive water chemistry also showed spots after the first year, which became larger and more interconnected over the second year.

The pool with balanced water chemistry also showed some spotting. “This data supports the ... hypothesis that even the most accurate water balancing and maintenance cannot fully prevent surface deterioration,” the study read. “It becomes evident that the combination of balanced water chemistry and the usage of more durable plaster materials is the only probable solution to the durability problems over the long term.”

Other studies lead the group to state that a combination of strengthening additives combined with properly maintained water would serve as the best prevention for a variety of problems, including spot etching and etching deterioration.

OnBalance’s research

Where the NPIRC conducted studies in controlled environments, onBalance derives much of its beliefs from analyses performed on plaster samples taken from real-life pools.

Over the years, the company has sent these core samples to multiple labs for petrographic analysis, whereby the chemical and physical characteristics of the materials are examined. Accompanying the core samples would be a series of questions, including what the water-to-cement ratios were in the spotted versus unspotted areas, whether there was evidence of aggressive chemistry in areas not showing spots and, if aggressive water was present, whether it alone could have caused the problem.

In one of onBalance’s most recent efforts, it sent samples from an unnamed pool in California to four laboratories, to allow for differences among various petrographers. Each lab used slightly different methods and equipment to conduct their examinations, including petrographic analysis to examine the spotting for physical signs showing how it occurred, as well as a chemical analysis to check the chloride content, which can indicate the addition of calcium chloride.

The labs agreed that the spots were, indeed, more porous than the surrounding material. “... The increased porosity in the sub-surface zone beneath white spots is attributed to some localized leaching, redistribution or decalcification of the past, probably through interaction with pool water,” said one petrographer, who was asked to summarize the reports from the four labs.

One of the labs concluded that the spots were found where small defects had formed in the surface. “The cracks allow ingress of water and allow for circulation of water through the crack network,” said the study from Wiss, Janney, Elstner Associates Inc., in Northbrook, Ill. “Interaction between water and the cement paste results in localized leaching and redistribution of the paste constituents.”

Scientists from three of the labs also believed that excess water may have been added to the material during troweling. They stated that the water-to-cement ratios seen throughout most of the pool was moderate to moderately low. But the areas near the spots showed “locally soft cement paste [which] may be an indication of locally elevated [water-to-cement ratio] associated with trowel finishing of the plaster surface (possibly with water applied to smooth the finish),” said the summary from River Bend Petrographics in Spring Green, Wis.

All four labs detected elevated chloride levels. However, there was no discussion of whether the calcium chloride fell within the 2-percent limit stated in the NPC’s Technical Manual. There also was little discussion regarding a relationship between use of the admixture and the spotting.

But through the years, onBalance often contracts with single labs to study problems in particular pools. In 2012, a core was taken from an Arizona pool exhibiting spots. The petrographers at the lab concluded that the spots occurred because permeability or flaking, often directly over aggregate particles, allowed carbon dioxide to penetrate the material and react with certain components of the Portland cement and result in carbonation. “Carbonation appears to have whited the affected paste, creating the white spots …” the report stated. Areas with no spots had not experienced carbonation, the report added, as evidenced by the existence there of a thin “mineral skin” that forms over a newly plastered surface. The breaching of this mineral skin is what leads to the spots, the study said. A halo effect is created as carbonation extends under the “skin” and away from the center of the spots.

The porosity and water-to-cement ratios of the sample were reported to be generally low. The lab stated that the spots may have formed because of higher water-to-cement ratios that were localized and caused by troweling technique.

Petrographic analyses performed on samples from other pools concluded the same thing, that the spotting was a result of leaching that occurred in areas where the water-to-cement ratio was higher than surrounding areas.