Pool builders and service techs that start up a freshly plastered pool know it can be a real pain. Plaster dusting is just the tip of the iceberg. For residential pools especially, most pools get filled within hours of finishing the plaster. That means the pool water and its chemistry is immensely important in the curing process (hydration) of new plaster.
According to the National Plasterer’s Council (NPC) startup guidelines, after filling the pool with water, it is vital to follow their startup procedures in order; first on the list is to test pH, alkalinity, calcium hardness and metals.
The three biggest reasons plaster damage occurs
In speaking with dozens of experienced pool builders and a pool plaster experts, doing a proper startup can avoid the vast majority of plaster problems. The three biggest reasons plaster damage occurs are:
- Alkalinity is too low
- Calcium hardness is too low
- Lack of a quality scale and metal sequest in the water
Items (1) and (2) go hand in hand, as both alkalinity and calcium hardness serve as buffers of pH…but they are also critical to the integrity of new plaster as it cures. Item (3), however, deserves more explanation, because it is where the biggest difference can be made.
Scale and metal sequest: the basics
Sequestering agents promote the bonding of molecules to metal ions. In pool water, a sequest bonds to dissolved metals, preventing them from falling out of solution—and subsequently adhering to things like plaster (metal staining). Without an effective sequest, metals and minerals can damage plaster.
But not all sequests are equal. Most in the marketplace are phosphonic acid-based, which, of course, introduces phosphates into the pool. As we have discussed before, phosphates in pool water are a nutrient source for algae. If you use a phosphate remover in your water, adding a typical metal sequestering agent will conflict with it, virtually negating both products. These are not inexpensive products, so it’s money that is being wasted, and pool water that is not getting the benefit of either product.
How to use SC-1000
The link here is where you can find Orenda's startup guide with SC-1000 dosing instructions. Add the needed dose of the entire pool as early as the first 200 gallons are in the pool, so as the filling process continues, the water is treated adequately. Correctly dosed sequest in the water should effectively prevent metals from staining the new plaster. This is especially important during the initial fill.
Calcium Hardness and Alkalinity, revisited
Both calcium hardness and alkalinity have to do with the pH of the water, as they are both buffers for it. Some builders do an acid startup to reduce plaster dust (calcium hydroxide), which can settle on the bottom of the pool and re-solidify. It’s basically when calcium extracts from the plaster because the water is acidic or not adequately saturated (see our article on the LSI). Too much acidity will cause damage to plaster, however, which can make it rough and porous (known as etching).
On the other end of the spectrum is an alkaline startup, by using more sodium bicarbonate. Along with this, add calcium to the water as early as possible, to prevent the surface from "donating" its calcium to the water. The first several weeks are the most vulnerable for plaster, so protecting it while it cures is essential for the lifespan of the surface. Some plasterers will finish a job, acid wash it, then spray it with sodium bicarbonate to neutralize the acid after it cleans everything. Again, we recommend reading the NPC's startup guidelines.
PPPPP: Prior Planning Prevents Plaster Problems
The key with either method—acid or alkaline—is to maintain proper balance throughout the initial filling. Sequestering metals is paramount during this time, since most fill water has metals already in it. New plaster is prone to staining and discoloration. For that matter, all surfaces at all ages are prone to staining. Managing metals may not be something you need to do, but test your fill water to know for sure.
Make sure you have an even flow of water throughout the fill. Even a few minutes of pause can create a visible line in the plaster, according to some builders we have spoken to. We at Orenda recommend using our dosing calculator to check the LSI of your chemistry, and err to the side of higher LSI by raising alkalinity and calcium hardness. Scale is treatable...etching is not.