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Are All Color Pigments Good for Pool Plaster

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There are two important issues involved when trying to achieve quality colored pool plaster that will remain durable, attractive, and the proper shade for many years.

The first issue is to utilize superior workmanship practices to achieve good color, with minimal mottling, and no blotchiness, white streaking or soft spotting, which our previous email update addressed. (Note: Some pool owners prefer the slight mottling variation that is normal for colored plaster).

The second issue is using quality color pigments (added to plaster mixes) that will hold up well for years and not lose its’ color in a swimming pool environment, which is the topic of this update. One would think that all color pigments used in pools are colorfast, meaning that the color doesn’t fade or become bleached in chlorinated water or in sunlight.  Sadly, that is not the case.

What has been learned?

The onBalance team has conducted many experiments with various pool plaster products, such as pebble and quartz exposed aggregate products that contain color pigments.

It appears the plaster products that contain “organic” pigments become bleached (loss of color) over time when subjected to chlorine (an oxidizer). But products with “inorganic” pigments generally do not become bleached. Additionally, experiments which subjected both organic and inorganic pigments to LSI aggressive water showed that neither type of pigment lost their color from etching.

When an organic pigment, phthalo blue for example, is bleached and loses its color over time in chlorinated water, the plaster surface becomes “whitish” because it is made with white Portland cement.

However, it was also observed that when two (or more) color pigments are added to a plaster product mix to obtain a unique and special color, and the blue organic pigment became bleached and faded, the other color pigment(s), if inorganic and colorfast (often a gray or brown pigment), remains unaffected, intact, and becomes the dominate color.

Obviously, only pigments that are colorfast are appropriate for swimming pool finishes.

Question: Why would material manufacturers and plasterers sell and use non-colorfast pigments that will not keep their color? One reason may be that organic (non-colorfast) pigments are usually much cheaper than the superior (colorfast) inorganic pigments. Of course, that allows some companies to underbid the quality-oriented companies.

Who Takes Responsibility or Not

The NPC has a Technical Bulletin addressing common color pigment problems. Amazingly, their bulletin does not mention anything regarding colorfastness and that (organic) color pigments can be bleached by chlorine or other oxidizers. Plus, no acknowledgement that excessive water troweling can cause white streaking, soft spotting, or blotchiness to slowly develop over time. And no mention that calcium chloride (hardening accelerator additive) should not be used with colored pigments as manufacturers WARN against, as it also contributes to severe blotchiness.

Instead, the NPC suggests that “aggressive water” causes color fading or whitening of colored plaster (along with causing many other plaster defects and discolorations), all of which is false. Of course, calcium scaling can mask the color, but that can be easily determined and rectified.

The plaster industry has misled the industry that water chemistry has the most significant and negative effect on the durability and color of plaster. To the contrary, there are various plaster/cement studies that have shown that poor workmanship and materials have a greater effect.

Think about this: Plasterers and material manufacturers generally recommend performing extremely aggressive “acid bath” or “hot start” treatments on new plaster and exposed aggregate finishes to accentuate the color or to remedy some discolorations. If those acid treatments aren’t causing plaster defects or discolorations, then on what basis do they claim that slightly aggressive water during Start-ups or afterwards causes all unsightly plaster problems?

Bottom Line: Using quality materials, including colorfast pigments, and superior workmanship will best ensure a durable and attractive pool finish for 20 years or more. That is what my father’s plastering company provided for their customers.

For photos of bleached pigmented plaster and more detailed information, click on these two links:


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