As we finished our first black bottom of the season yesterday, and I'm getting ready for a walkthrough with homeowners, I need to tell them about possible changes with their new pool, and main one is calcium build up and calcium deposits, that are particularly more visible on darker finishes. That inspired me to write this post with about everything that will happen with your new black pool, and not to worry about it (if we are your contractor :) if we are not your contractor, feel free to call us for free support for your #plastercare I'll be happy to help and answer any question).
I will start with new plasters and most common reasons for loss of color:
Calcium Salt Migration Due To Cement Hydration (pigment masking)
Precipitation of Minerals or Metals (surface scaling)
Dissolution of Cement Compounds (Pigment Loss)
Cement Hydration is basically the chemical reaction that converts dry cement powdered materials and water into a rigid structural material, or binder. While approximately 70% of cement hydration takes place in the first 7 days from the time of mixing, there is still a significant amount of hydration that will take place over the next 28 days (to approximately 85% of cement hydration). The remaining unhydrated cement will continue to hydrate for years after placement. However, the pigment that is dispersed throughout the cementitious material during the initial mixing of the material becomes locked into place once the cement reaches final set.
Though the pigment is no longer free to move or disperse after final set, cement hydration continues. A byproduct of the cement hydration reaction is a salt (calcium hydroxide), which ionizes in the presence of moisture and is free to migrate throughout the interior of the finish coating. These calcium hydroxide ions can settle out, or precipitate to form a white crystalline deposit that can cover, or mask, the coloration of the finish.
For swimming pools, the greatest potential for pigment masking is on newly installed finishes within the first 3-days after the pool is filled with water. Adhering to a proper start-up procedure is important. Removal of any calcium hydroxide that migrates to the surface (plaster dust) is also important. Calcium hydroxide (plaster dust) should be removed and filtered out of the water within the first 3-5 days after the pool is full or it will carbonate and adhere to the surface. Calcium carbonate can be difficult and expensive to remove.
Now about calcium deposits on new plasters that form more during wintertime.
This can be annoying to both pool pros and homeowners. I usually try to convince homeowners, instead of plastering later in the season, to plaster next spring but have pool full and filtering as long as possible and winterize as late as possible, and this is why.
Crystals have been forming in newly plastered pools at a high rate during winter. In addition, these calcium deposits are different in structure and form that the common calcium scaling problem that typically develops on pool surfaces due to out-of-balance pool water.
From various reports, this problem seems to occur more often in the northeast of this country where winter temperatures are very cold. When confronted with these unusual looking "crystals", some industry pros are at a loss to explain or consistently prevent them from forming on new plaster surfaces. Some pros thing this is because of the aggressive water. That theory holds that the pool water is not being properly winterized by adjusting for the soon to be lower cold water temperatures that can make the water more aggressive. Then, that aggressive water dissolves calcium from the plaster, and then, somehow reverses that process and results in calcium crystals growing on the plaster surface.
The unique calcium crystals are generally not discovered until the spring when pool covers are removed. In such cases, after testing the water, the pH is found to be very high, often above 9.0. but aggressive water doesn't do that. Interestingly, the crystals are not found in all areas of the pool.
It is worthy to note that the American Concrete Institute, and Portland Cement Association have documented that cement quality plays a huge role in the amount of efflorescence and/or dusting (among other problems and defects) that develops on new concrete and cement surfaces. They cite the possibility of misapplication of plaster, instances such as adding a high-water content while mixing, using a high calcium chloride content, and poor troweling techniques (using excessive water while troweling) as reasons leading to a weak, porous, and excessive microcracking cement finish. Those are the issues that enable ad result in calcium efflorescence (from calcium hydoxide and calcium chloride) to form on cement surfaces. The same problems exist with pool plaster.
Some plasterers add a high amount of calcium chloride (hardening accelerator) to plaster mixes during colder temperatures to speed up the plastering application so that it doesn't take all day. As mentioned above, doing so leads to calcium hydroxide and calcium chloride dissolving out of plaster over the winter regardless of the water balance. And that will raise the pH significantly, which also means the LSI increases beyond the norm (above +0.8). That is a recipe for calcium crystals to develop. It is also likely that stagnant water and lack of brushing during the winter can contribute to the calcium crystals forming and adhering to the plaster. This is why we don't schedule or recommend any withers outdoor work. It's just easier not to take those risks and not to worry about remedies.
If issues like this occur, there's a number of treatment that we can do, after we complete trouble-shooting inspencion. During my inspection of defects and failures, generally one of more of the following is involved:
*improper mixture proportioning
*improper surface preparation
*improper placement of finishing techniques
*improper water cure
*delayed or improper water fill of the swimming pool
*improper chemical balance of the water of the pool
*improper maintenance of the swimming pool
*structural movement forces
*some combination of the above.
Often, investigation utilizes the combination of an expert in the swimming pool plastering field and failure analysis laboratory.
If we were not the installer, I will ask for:
*date of installation,
*date of initial complaint,
*substrate preparation,
*mix design components and mix design proportions,
*mixing procedures,
*finishing techniques,
*qualification of personnel,
*installation issues,
*weather records,
*fill and start up procedures,
*ongoing service and maintenance of the swimming pool,
*all available water chemistry records of tap water and pool water (from feeling to present)
*any other information that may be helpful in understanding the cause of the defect, failure, or service maintenance issue,
*listing of the responsible parties for each of the above-listed events.
Remedies depend on the size of the damage. Sometimes the repair is as easy as lightly sanding or grinding the surface of the coating, by acid washing or bleaching the surface, by the use of certain stain removers or chemical treatments, or by removing and patching the affected area. Sometimes more complicated treatments are needed, but I will leave that for future post.
Thank you for being here!
Jelena