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What Pool Plaster Needs before Start-up

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In order to ensure a long-lasting and stain resistance finish, new quality pool plaster (including quartz and pebble) requires at least six to eight hours of proper curing (humidity) before filling with water, and requires the fill water to have a positive Saturation Index (LSI) of about +0.5.

If new pool plaster is submerged in water too early, or the fill water is low in calcium hardness and alkalinity (negative LSI), some plaster material will dissolve from the surface, creating porosity and weakness, and will then be more susceptible to future staining or lightening.  All of this occurs before the service tech arrives to perform the chemical start-up program.

Can a service tech know if some plaster material has been dissolved off the plaster surface?  Yes, by the amount of “plaster dust” that has settled on the bottom of the pool.  More damage can occur to a new plaster surface during filling than during the following month.

The reason that a new pool plaster surface is so vulnerable at first is due to the fact that it contains about 15 to 20 percent calcium hydroxide.  Calcium hydroxide is soft, slightly soluble, the weakest component of pool plaster, and is dissolved by typical fill water at the surface.  The LSI is applicable to calcium carbonate, not calcium hydroxide.

As much as 20 pounds of calcium hydroxide can be dissolved from the plaster surface of a 20,000 gallon pool, depending on the workmanship, fill-delay, and aggressive fill water conditions. The calcium hardness of the fill water can increase 50 ppm to 100 ppm upon filling. 

It is the dissolved calcium hydroxide that becomes “plaster dust” (in the water) as much of it is transformed into insoluble calcium carbonate by the pool water.  The amount of plaster dust formed can indicate how much material has been lost from the pool plaster surface. The more material that is lost, the more porous and rougher the plaster surface is (as seen under magnification), the less durable it is, and the more likely dirt, iron, and copper will stick to the surface as time passes. And weeks or months later, when the plaster surface begins to look aged and stained; the improper filling program the pool received may be overlooked as the cause. 

A Bicarb Start-Up chemical program (as promoted by onBalance) ensures that the fill water is appropriate (a positive LSI) for filling a new plaster (and quartz) pool.  It prevents the loss of calcium hydroxide from the plaster surface, which preserves a dense (non-porous) surface, and with no plaster dust forming.  It does that by converting calcium hydroxide on the plaster surface into calcium carbonate, creating a harder, denser, smoother, and more durable surface.  If everything is done correctly, there will be no increase of calcium hardness in the pool water.

Because the plaster surface is smoother, dense, and more durable, it stands up better to future acid washes and dirt and mineral stains are easier to remove. Dark colored plaster stays darker and does not become blotchy or lighter in color.  Long-term esthetics is definitely improved.  Acid start-ups can be one reason for colored plaster and quartz finishes becoming blotchy and lighter in color.

For the past 15 years, many pool plasterers and service techs report having great success with the Bicarb start-up method. 

For the Bicarb start-up:

The above pictured pool/spa combo, featuring black plaster, was set up as a Bicarb start-up. You can see the barrel and hoses in the background. When we came back, the pool was crystal clear, but the spa looked like it was full of milk (especially once we brushed it!). The homeowner had come home and decided to fill the spa using non-bicarbonate tap water. What a difference!

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Comment by Wes Burdine on September 9, 2013 at 2:15am

Hey Kim,

I have a good friend in the Atlanta area how is considering converting his liner pool to a plaster pool.

His pool is 25 x 40. He wants to convert it to Plaster, with approximately 2' to 9' depth.

Do you have any recommendations for people in this area and estimated costs?

You can reach me here or via email:


Comment by Jeremy Hine on September 8, 2013 at 6:30am

wow. never saw, nor heard of this before.  I'm looking forward to sharing this with the guys and to try this out.


Florida Leisure Pool & Spa

Comment by Rex Richard on September 6, 2013 at 1:01pm

Thanks Kim!  Great information!

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