Calcium Scaling versus Porosity Issues
Calcium scaling is caused by out-of-balance water and usually deposits a layer of calcium carbonate throughout a pool causing the surface and fixtures to whiten. It even feels rough to the touch. Light scraping or sanding with sandpaper will take this away.
If the whitish discoloration appears as streaks or blotches and is smooth to the touch, the problem is probably not calcium carbonate scaling, but rather a porous surface that is deteriorating faster than normal.
Calcium hydroxide and calcium chloride are two factors reduced by the plaster in a pool when it’s cured. These two things can lead to a porous, yet smooth surface. Calcium carbonate, a primary plaster constituent, is insoluble. It’s easy to assume that calcium hydroxide and calcium chloride can only be dissolved by aggressive pool water, when in fact, both elements can actually be dissolved, even by balanced water. That means’s likely something other than aggressive water is the culprit for porosity developing and the whitening effect. When those calcium ions slowly dissolve away, that process can remove color pigment and is another reason for a whitening to develop.
Other Reasons For Discoloration
Another reason for color loss is that some plasters use organic pigments in their mix. Organic pigments can be bleached by the presence of chlorine or other oxidizers, and even by direct sunlight.Organic pigments are less expensive than inorganic pigments, but they generally cannot withstand a swimming pool environment for long. This bleaching action occurs even if the plaster workmanship is of high quality. Some plaster mixes contain two pigment colors. If one is organic and becomes bleached, that color will simply disappear leaving the other non-bleachable pigment visible as the sole color.
A Remedy Porous Plaster
A very extreme acid treatment is often implored to restore the original color of the plaster. However, these acid treatments etch the plaster and make the surface rough. This also causes increased porosity and surface deterioration. It reduces the life span of the pool surfaces and the pigment color is likely to fade away and turn whitish again.
A better alternative for removing a porous and whitened plaster surface would be to sand and polish the plaster. This removes the porous material and restores a hard, dense, and smooth surface to the pool. Unfortunately, for pebble finishes, sanding and polishing is virtually impossible, leaving the more harsh alternative as likely, the only option.