The NPC has stated that pool water must be maintained with a Langelier Saturation Index (LSI) between 0.0 and +0.3 for plaster pools (no negative LSI is allowed), and that disregarding those LSI parameters promotes white spotting, etching, and discoloration on the negative side.
Yet the NPIRC Phase 3 (2005-2006) study demonstrated that typical white pool plaster (Section C in Pool 5) can withstand negative LSI’s (from -0.1 to -0.4) one-third of the time over an eight month period without any visible etching, spotting, craze cracking, or discoloration. That pool section was rated “zero” in all three categories.
It is apparent that the workmanship of the white plaster section (C) in Pools 5, 6, and 9 was better than the Phase 2 test pools. According to the report, section (C) was plastered with only one percent calcium chloride added, with a better water-to-cement ratio (.46) instead of (.50). Perhaps better plaster finishers were also used.
By comparison, several test pools in Phase 2 deteriorated and discolored in slightly positive LSI water within just six weeks’ time, and had white spots within four months!
What the above means is that a negative LSI of -0.1 to -0.3 is not overly aggressive and does not cause white spotting and gray discoloration, as the NPC claims. Those slightly negative numbers are within the “balanced” range (-0.3 to +0.5) as established by the APSP. Furthermore, even very aggressive water does not cause white spotting or gray discoloration. It simply etches a quality plaster surface uniformly over time.
The NPC has ignored the real evidence and misrepresented the results of their own study. It is time they acknowledge that poor workmanship practices cause specific plaster problems.
NPC Certified Start-up Technicians should be concerned. There are reports that start-up people have been blamed for various plaster problems even though the pool water was properly started and balanced. See “IPSSA Member Victimized for $6,000” Link: