Solvents to Remove Paint From Flagstone Patios

The Upside of the Accident

• Removing accidentally applied paint from “finished” surfaces -- such as varnished timber and painted furniture -- and from material that can be deformed by abrasion and chemicals -- such as vinyl and plastic -- requires a delicate touch and carefully chosen solvents. Flagstones typically cannot be damaged by either harsh tools or chemicals, so even using a pressure washer with a medium tip is unlikely to damage the masonry. Stripping the unwanted paint with solvents is a great option for patios where a pressure washer cannot be used.

Ideal Time to Use Solvents

• Only work on dry flagstones and when rain is not expected. Starting out with a wet surface will dilute the solvent and reduce its performance and being caught by a rainstorm partially through the job could cause the chemicals to be washed into flower beds, onto the lawn or into the drainage system. The latter scenario is bad for the environment and might be illegal.

Preparation

• Use a paint scraper, a putty knife or an old wood chisel to remove any “depth” from the paint spill; using solvents to loosen and remove thick patches is not only wasteful and costly, but radically increases the chances that contamination with adjacent, undamaged surfaces could take place. Further, scrapings that are removed dry can simply be tossed in the regular trash; local ordinances may govern what it is legal and illegal for the disposal of chemically treated waste. Once the depth is scraped away, use course sandpaper to take the spill right down to the surface of the flagstones, leaving only a stain in the porous surface.

Commonly Available Solvents

• Phosphoric acid is sold for masonry cleaning at most hardware stores and in the do-it-yourself aisles of department stores. Although not available from these locations in particularly strong concentrations, it works well to interrupt most paints. The proprietary concrete and grout cleaners available at most home improvement superstores may also work. Both contain phosphoric acid, emulsifying chemicals and surfactants that are blended to produce an excellent result with little danger. Trisodium phosphate, almost universally packaged and referred to as TSP, is another cleaning product that is good at removing most paint types.

Muratic Acid

• Muriatic acid, otherwise known as hydrochloric acid, is a powerful liquid solvent. The excellent results achieved are tempered by the dangers inherent in its use. Although sold for amateur application, it is extremely dangerous and should be reserved as the last resort unless you have experience in its use and handling. Muriatic acid prepared and sold for home use is usually a 31.45 percent acid content, mixed in water; it must still be treated and used with great caution. Muriatic acid burns through clothing, metal and even some of the plastics used to manufacture non-product-specific protective clothing; its vapors burn and scar human tissue -- including the lungs and nasal passages -- quickly. Adhere to all the manufacturer’s usage instructions and precautionary directions. The reaction of the acid with the spilled paint and the alkaline surface of the flagstones will result in a powdery white residue when the acid has dehydrated. This can be removed with a shop-vac, and the area then rinsed with water.