Kim – Acid Start-ups and Plaster Dust

When typical balanced tap water fills a new uncured plaster pool, some of the plaster material can be dissolved and removed from the surface. Therefore, if balanced tap can dissolve new plaster, what happens when Acid (aka “Zero Alkalinity” or “Hot”) start-ups are performed on new plaster?

The onBalance team has studied the effects of acid start-ups. Depending on the amount of acid added and the duration of time, acid start-ups can dissolve and remove about 10 to 30 pounds of plaster material from the surface of a quality applied 20,000-gallon pool. Under magnification, the plaster surface will be slightly etched.

When adding acid to reduce the alkalinity to zero, the result is a very low pH (4.5) and a very negative LSI (-3.0 to -4.0). That acidic condition also dissolves the plaster dust (which is primarily calcium carbonate) that formed, which then increases the calcium level of the water by about 50 to 180 ppm.

As confirmation of the above information, the Cal Poly/NPIRC/NPC Phase 3 pool study also performed “Zero Alkalinity” start-ups on 4 pools. The data shows that the beginning calcium level was about 130 ppm once the pools were filled. After the acidic (Zero alkalinity) start-up process was completed, the calcium level of the test pools had risen to about 300 ppm.

Even though the aggressive water had etched and leached away many pounds of calcium from each plaster test pool, Cal Poly reported that the white plaster sections had virtually no visible etching, craze cracking, or discoloration after 8 months of time. And there was no mention that any test pool had developed white spotting or streaking (spot etching), gray mottling or streaking, calcium nodules, or spalling (flaking).

Acid start-ups are often performed on color pigmented pools by plasterers to ensure a darker and more uniform color. And it works… for the short term.  Unfortunately, severe acidic treatments will likely reduce the longevity of the plaster by a few years, and result in earlier staining problems.

Along these same lines, for colored quartz and pebble pool finishes, material suppliers and plasterers commonly advise service techs and pool owners to maintain the pool water in a slightly LSI aggressive condition to prevent (or remove) a “whitish” film on the surface due to calcium scaling.

That brings up a major inconsistency within the pool industry. Since acid start-ups and maintaining negative LSI water is how to prevent a whitish discoloration developing on colored plaster (including quartz and pebble finishes), then why is it being claimed that aggressive pool water causes colored plaster to develop variable white areas, spots, and streaks? Yet, this is what the NPC has been telling pool owners.

As mentioned above, we know that at Cal Poly, aggressive water did not develop white “soft” spots (spot etching). It is also known that acid treatments do not remove the white spotting problem.