Q: We've been asked to remove paint from the brick walls of an old building. We're a sandblasting company and we normally sandblast walls to remove paint. But sandblasting, we're told, could damage these soft brick walls. What other ways could we remove the paint?

A: You are correct. Sandblasting soft brick would remove the surface of the brick as well as the paint. Removing the surface layer may create an unsuitable architectural appearance and also promote further deterioration. Future cleaning agents or air pollutants probably would penetrate the opened pores.The method you should use depends on the type of paint and whether you're removing paint spots or paint from an entire wall. The paint type can easily be determined by sending a small flake of paint to a chemical lab. Once the paint is identified, an organic cleaner can be chosen.If you're removing small paint spots, try using a poultice so you don't smear the paint over a larger area. A poultice is a chemical paste that dissolves and loosens the paint as the paste dries. The poultice also absorbs the paint, instead of letting it be reabsorbed by the masonry.In general, only chemical paint removers, either alkaline strippers or organic solvents, can completely remove paint. Alkaline strippers are generally more economical and work particularly well on old linseed oil-based paints. They can cause efflorescence, however. Organic solvents, such as methylene chloride, dissolve the organic components of the paint, causing the paint to swell and form a gel. Organic solvents tend to be more expensive, but they can dissolve most types of paint as well as urethane varnishes and epoxy.

However, they also can spread spot stains deeper into the masonry and are toxic, requiring special handling and storing procedures.Most manufacturers require that you wet the wall before you apply the chemical paint remover then rinse the wall thoroughly a specified time after applying it. Wetting the wall before minimizes the amount of cleaner absorbed by the brick. Rinsing afterward washes the chemicals away so they don't damage the brick. The chloride in organic solvents, for example, can attack the metal in the window frames or the reinforcing ties in the masonry. For this reason, all surrounding areas should be covered and protected from the chemical cleaner and the rinse water. Normally, you should rinse the walls until the wash water has a pH of 7, measured at the jobsite with pH papers.To determine the best chemical cleaner, you need to contact a manufacturer of paint cleaning solvents and follow his recommendations. A few companies are listed below.
ProSoCo Inc.
P.O. Box 171677
Kansas City, KS 66117
Telephone: 913-281-2700 American Building Restoration Chemicals, Inc.
9720 S. 60th St.
Franklin, WI 53132
Telephone: 414-761-2440QRB Industries
3139 U.S. 31 North
Niles, MI 49120
Telephone: 616-683-7908