One of the newer methods for handling plaster surface discoloration is to use a blowtorch to apply heat to the plaster, a process called torching. It has been touted as an inexpensive way to eliminate severe discoloration and pool stains.

Some badly discolored pools seem not to respond to acid washes and for aesthetic reasons might need to be entirely replaced.

It is said that torching can be used in a variety of situations, including:

• Discoloration from water from inlet fittings.

• Bath tub rings.

• Drip marks.

• Water from the back side of the structure.

• Calcium chloride issues.

• Low calcium hardness fill water.

• Scale.

• Cleaning system track marks.

• Differences in surface thickness.

• Etched surfaces. Best of all, these stains and discoloration can be remedied relatively cheaply. One needs a sump pump, shop vac, acid washing equipment, 3 to 4 propane tanks, abrasives and polishers, weed burners, plus some specialty equipment like rubber boots and polarized sunglasses.

The process begins by draining the pool and then lightly acid washing the plaster. For a 20,000-gallon pool, at least two workers are needed to apply heat to the surface using propane blowtorches that are burning “true blue” or clear flames. Polishers, like diamond hand pads, are used to buff out any rough spots.

The torching is recommended to take place slowly, over a period of several days, because otherwise only the surface will be affected and stains penetrating more deeply into the plaster will not be affected.

Stains and surface discoloration do seem to be diminished in this manner, but the reasons and the possible costs are not entirely clear.

Scientists have proposed the following reason for the lightening effect when the plaster surface is heated: Entrapped moisture is extracted from the plaster when it is heated. Simultaneously, calcium hydroxide present in the plaster is converted to calcium carbonate in the presence of carbon dioxide in the air.

Ca(OH) 2 + CO2 ↔ CaCO3 +H2O By slowly torching the plaster, the carbonation process penetrates the depth of the material while simultaneously releasing trapped water. This process may result in increasing the plaster’s porosity, and that increased plaster porosity may be the reason for its lightened appearance.

So while it is possible to reduce plaster surface discoloration via torching, it is achieved by compromising the plaster ’s integrity.

Image credit: Pool Troopers