Plasterers conducted several research experiments in the 1990's to determine the cause of spot etching. One of these experiments was a test pool in Phoenix Arizona, performed by what has been referred to as the "Arizona Plasterers Council".

In 1990, this test pool was resurfaced with eight different plaster sections comprised of different types of cement and aggregate. This test pool was filled with water, and was maintained in a balanced condition for a few months, and then with aggressive water the remainder of the year.

When the plasterers drained the pool for an inspection after one year, they noticed spotting in all eight sections.

What did the researchers claim? They announced that aggressive water chemistry was the only common denominator which caused the spotting to appear. They claimed that all plaster sections had spotted.

A year later, onBalance looked at this pool, accompanied by a member of the trade press. We noticed a few things that the plasterers had not shared with the rest of the industry: Some sections had nearly 80% of the plaster surface covered with spots, but one or two sections had only about 20% of the surface spotted, with large areas of these sections completely unaffected!

In addition to the difference in the severity of the spotting, the patterning of the phenomenon varied from section to section - and at least some of the patterning was directly attributable to troweling patterns!

In later NPC meetings, when this pool was referred to as "proof" of a chemical cause for spotting, the plaster company participants were asked why the difference on the amount and patterning of the spotting from one section to another, and how and why could water affect each section so differently? If water chemistry was the sole reason for the spotting, wouldn't it affect all of the plaster sections consistently?

They were also asked how much calcium chloride (CC) was added to each plaster section. They would not respond to our questions.