The Art of Good Pool Plaster Color
An attractive plaster color (other than white) is often preferred by pool owners. However, it is very difficult for plasterers to produce a uniform and consistent color. The reality is that there will always be some minor shading (mottling) and variation in the color and can never be uniform looking like paint or fiberglass.
One of the primary reasons for non-uniformity is that pool plaster a hand-finished product. It is plastered by multiple finishers and subjected to a variable environment during curing. Most pools are also plastered using multiple batches of material which will never match precisely.
Pool owners need to accept that reality. In fact, the National Plasterers Council (NPC) appropriately recommends that a “Disclaimer or Waiver” be provided to pool owners to explain that there may be slight differences in the color shading.
Fortunately, quality-oriented plaster companies know how to produce a relatively good-looking color finish that will satisfy most pool owners. Along with other good practices, such as tenting pools to control temperature and humidity, they use colorfast pigments, a low and consistent water/cement ratio in all batches of material, they do not add any calcium chloride and do not add water to the surface during the troweling process. Lastly, they achieve a smooth finish with a properly-timed final troweling before the plaster becomes too stiff.
When the Color goes Bad
Obviously, poor chemical maintenance can either etch or scale any surface, including colored surfaces, but those are known and accepted phenomena. There are two non-chemical reasons for color problems developing with new plaster finishes, including quartz and pebble finishes. They are workmanship and materials.
When a pool is plastered too fast, due to adding too much calcium chloride set accelerant, the plaster surface can display severe and irregular mottling, color fading, or white blotchiness, streaking, and spotting. Also, if other quality workmanship practices, such as proper troweling, trowel pass timing, water/cement ratio, refraining from wet troweling or propane torching, etc. are not followed, increased negative effects may plague the surface aesthetics. And understand that those ugly discoloration problems generally take a few months to worsen and become increasingly visible.
Of course, a “Disclaimer or Waiver” document should be not used as an excuse by plasterers to avoid taking responsibility for their work quality.
The above discoloration issues are not caused by aggressive water. If it did, then colored cement driveways and walls (on buildings) would have similar results when rained upon (which is aggressive water). Yet, they do not because they are usually applied properly.
On other hand, overly positive LSI pool water can cause calcium scaling and can mask the colored plaster with a whitish deposit. When that happens, acid (aggressive water) treatments are often performed to remove the white discoloration and darken the plaster color again. Also, many quartz and pebble companies recommend maintaining the pool water slightly (LSI) aggressive to prevent the general whitening process from occurring altogether.
Therefore, aggressive water cannot be the cause when it removes the “white discoloration” and darkens the plaster color. And there are no plaster studies showing that slightly (LSI) aggressive pool water causes irregular white blotchiness, splotches, or streaking in colored (or white) plaster pools to appear in just a few months.
Evidence from plaster/cement petrographic “forensics” studies show the cause and effect relationships between color surface failure and improper workmanship practices. See this link for reports on this topic. http://www.poolhelp.com/home/onbalance-research/consulting/
The Bottom Line
Good workmanship standards are needed for the pool plastering trade.