@lasvegaspools
Thank you for sharing your perspective about plaster spotting.
Point One: Regarding the statements (that you provided in your post above) from several cement petrographers. It is important to realize that when discussing the dissolving capabilities of water, some statements can be easily misunderstood. And I believe that is the case with those statements.
I will try my best to explain in detail. Not all petrographers are chemists (and especially not pool water chemists), and we learned years ago that some petrographers consider the dissolution (dissolving) of any cement/plaster material as being an “aggressive action” by water regardless of what the LSI is. Since the LSI only predicts solubility of the carbonate form of calcium, and the hydroxide form can be soluble up to a pH of 10, the LSI as used in the pool industry is not always being considered when petrographers make statements about “aggressive” water.
First, with respect to water dissolving calcium carbonate (a relatively insoluble and major component of plaster), the entire pool industry (including onBalance) would agree that the water must be LSI aggressive to do this because balanced water does not generally dissolve calcium carbonate. If, however, the discussion is about the dissolution of calcium hydroxide (a soluble and 25% component of hardened cement/plaster), some petrographers (that are not considering the LSI) may still describe that dissolution of soluble calcium hydroxide by (LSI balanced) water as being an aggressive action. But a chemist (and understanding the LSI) would probably say that calcium hydroxide simply dissolves or will be “leached out” (a non-aggressive phenomenon) with the presence of water. In fact, calcium hydroxide is soluble enough to be dissolved (leached) away by even positive LSI water. And that is what is often taking place with spotted pool plaster. That is a major distinction to understand about this issue of spotting.
When analyzing spotted plaster, one must take the LSI into consideration when making statements about the water and what kind of water is dissolving calcium hydroxide. Otherwise, such statements can be easily misinterpreted and lead people into thinking that LSI aggressive water was the reason for the dissolving of calcium hydroxide and leading to white spotting.
It appears that water needs to be at least above an LSI of about +1.0 to not be aggressive towards and dissolve calcium hydroxide. (And even a higher LSI with respect to the extremely soluble calcium chloride (another typical plaster component).
It is that fact about the solubility of calcium hydroxide that plaster/NPC leaders are misrepresenting. They continue suggest that only LSI aggressive water dissolves calcium hydroxide. They put out a false narrative to mislead the industry and pool owners and to hide behind.
Therefore, quoting a general statement from a petrographer without context in this light does not further the understanding… one needs to nail them down on what “aggressive” means in terms of the actual plaster components exposed to the water. “Water chemistry,” whether balanced or aggressive, does play a role in the development of spotting, because without water, no dissolution occurs.
Point Two: You are mispresenting our position. onBalance has never suggested that aggressive water is never a factor in some spotted pools. If a plaster surface is compromised by poor troweling, then LSI aggressive water will likely cause spotting to occur much faster than would with balanced water. If however, the plaster surface has not been compromised with poor troweling aspects, then LSI aggressive water will uniformly etch the plaster surface, and there will not be a major whitening of the surface. In fact, you probably know that aggressive water (and acid treatments) does not turn colored plaster white. Instead, it brings out the original color.
We agree with the statements that if a poorly troweled plaster pool is maintained with LSI aggressive water, that aggressive water will certainly attack those compromised areas (soft plaster areas including craze cracks, plaster-to-tile transitions, and spots) quickly and result in white areas developing much faster than would happen with balanced water.
Also, with an aggressive condition, the surrounding areas (non-spotted) will also show etching effects. And that is what a petrographer can determine. So far, we have primarily sent unetched samples we obtained from failed plaster pools to petrographers. In one instance, however, the plaster had been previously acid washed. Therefore, in all but one of the cases the petrographers did NOT see any etching effects. That is evidence that aggressive water is not necessary to cause white spots. In the one etched sample the petrographer had to closely analyze to see the effects of the spotting since the later etching obliterated some of the surface features.
Is it your opinion that aggressive water is required to develop white spotting?
The bottom line here is that the plaster leaders know that they have no study and no science to support their position. I believe they know that calcium hydroxide can be dissolved by LSI balanced water. And I believe they know that the Cal Poly studies provided evidence that spotting can occur in balanced water.
As to your test pool challenge:
The onus is not on us to prove our position. We have retained four labs to study and analyze plaster samples and determine what causes white spotting and streaks. Their findings indicate that aggressive water is not required to generate white spots and streaks. Even the NPC’s Cal Poly test pools demonstrated the same outcome. If you feel we are wrong, and you are sure of your position, then the onus is on you to prove that.
We have already spent thousands of dollars of our own money to determine and verify a cause and effect. You can’t ignore the evidence that we have produced, and simply say we need to do more.
Balanced “water chemistry” does enable the slow and selective dissolving of the soluble compounds such as calcium hydroxide and calcium chloride. If the water is aggressive, the spotting should happen faster, but the aggressiveness is not causative.
As you say, there are multiple factors that contribute to white spotting development; water/cement ratios, water troweling (how much?), adding calcium chloride (how much?) and late hard troweling, and spraying down a pool before filling, etc. Telling us to predict when spotting will become visible is next to impossible because of the complexity of this complicated plaster defect.
Your challenge to conduct a test pool study with your set of criteria is virtually impossible. And ignores the science and what has already been proven by petrographers. The NPC should know how to spot a pool. They produced spotted plaster in several balanced water test pools at Cal Poly and filmed the troweling. But they haven’t shared their video with the industry. Perhaps they will share it with you.
It appears that you and the NPC are ignoring the fact that soluble calcium hydroxide is what gets dissolved away while leaving calcium carbonate on the surface. That reality is what proves that aggressive water is not required to cause spots, streaks, and blotchiness. But that is not to suggest that aggressive water is never part of some spotted pools. But when aggressive water is involved, it will also show etching (roughness) of a carbonated surface of the areas surrounding the compromised and porous whitened spots and streaks.
You used a Laura Powers quote. Did you know that she came up with a mechanical model for the cause of spotting?
Regarding our Test Pools: We do not have a projected finish date because of continuing delays in trying to obtain sufficient money, equipment, materials, and assistance. There have been active attempts by some to delay or sabotage assistance in this endeavor. I personally have been donating several thousand dollars each year towards this effort. We could use some help.
Lastly, I find it inconsistent and illogical for plasterers to claim that maintaining a moderately negative LSI water is a definite causative factor for spotting, and yet, they commonly perform strong acid treatments immediately after plastering or during start-ups and afterwards, and THAT does not contribute at all to spotting? Can you explain that reasoning?
And I have a question: Is it your position regarding gray mottling, spalling, and calcium nodules, that aggressive water causes those defects too?
Addendum:
When petrographers examine actual spotted plaster, instead of just making general comments, they say things like:
· Dr. Mengesha A. Beyene, Dr. Michael Silsbee and Niles Thaulow at the RJ Lee Group: “…relatively high water-to-cement ratio compared to the surrounding paste.” “…the porous, high water-to-cement ratio areas near the surface spots are likely the result of poor finishing practices such as retempering the cement paste by adding extra water during finishing.” “If aggressive pool water caused the observed off-white features, it should have affected the whole plaster surface more or less uniformly.”
· Dr. Boyd Clark at CTL Group: “…associated with areas of increased porosity in the plaster, due to water driven ‘reconstruction’ of the hydrated cement paste.” “The chloride values are the same throughout the plaster indicating chloride was added to the plaster during placement and are much higher than industry recommendations…” “Past studies have indicated that the swimming pool spotting phenomenon becomes more pronounced with increasing chloride content.”
· Laura Powers at WJE: “…the discolored spots represent localized distress, as evidenced by the abundance of microcracks, softness of paste within the spot, high secondary porosity, and the re-distribution of paste constituents (leaching of calcium from calcium silicate hydrate and precipitation of secondary calcite.)” “The distress does not appear to have been caused by exposure to aggressive water;” “Troweling practices that expose aggregates at the surface risk producing avenues for water ingress along the paste-aggregate boundaries.”
· Ronald D. Sturm at River Bend Petrographics: “…localized leaching of paste constituent, leading to increased micro-porosity and permeability, and color changes to the cement paste associated with localized carbonation of the affected, leached paste.” “This localized increase in w/c is likely associated with finishing practices, including suspected addition of extra water to the surface during finishing.”
(These four observations above were all from samples of a single pool, sent to four different labs to confirm / peer review findings.)
and then this happened right away. Super frustrating.
