What Cleans Soot Off Brick

Expert Insight

• Preservationist Anne E. Grimmer, in “Keeping It Clean: Removing Exterior Dirt, Paint, Stains and Graffiti from Historic Masonry Buildings,” examines the removal of soot from acid-sensitive masonry, such as glazed brick, and nonacid-sensitive material, such as unglazed brick. She categorizes soot as an industrial stain, as opposed to organic stains such as algae. She notes that one means of removing soot entails gently scrubbing the brick with a scouring powder containing oxygen-based bleach, which differs from typical chlorine-based household bleach. You may not be able to thoroughly remove the soot, but you can reduce its visual impact, she notes.

Poultices

• Grimmer and other cleaning authorities recommend alternatives as well. You can make a poultice -- a cleaning paste designed to be left in place -- starting with a powder such as baking soda, talc, whiting or kaolin, a fine type of clay, or even absorbent cotton. The liquid cleaner mixed with the base can be naptha, mineral spirits, methylene chloride, perchloroethylene, ethyl alcohol, acetone, ethyl acetate, amyl acetate, toluene, xylene or trichloroethylene. Most should be available at a well-stocked paint store. You apply a ½-inch layer of poultice to the sooty brick. If the poultice is neither too thick nor too thin, it can adhere to a vertical brick surface, or you may need to hold it in place with plastic mesh fastened with nonstaining holders, Grimmer observes.

More Formulas

• The Michigan State University Extension echoes Grimmer’s recommendations, also advising that you mix poultices to lift the soot off the brick. One recommendation is to mix soap, table salt and water, apply it to the sooty brick and remove it with a stiff brush. Shaved naptha boiled with water can combine with ammonia and pumice for an alternative compound to apply to the sooty surface. You can rub this off with a bristle brush followed by a rinse and another round with a strong detergent and a final rinse. Grimmer also suggests applying mineral spirits, brushed off the lifted sooty liquid and rinsing the bricks with water.

Testing Alternatives

• You can also dissolve trisodium phosphate in hot water to scrub the surface, Michigan State advises. Jeff Bredenberg in “2,001 Amazing Cleaning Secrets” recommends a variation: TSP mixed with a cola soft drink and water, sponged on the brick and scrubbed off after 15 minutes. Rinse with water and a clean sponge. Weathered brick more than 50 years old may be damaged by vigorous cleaning, so test a corner or loose brick to see if it can stand up to a cleaning method involving scrubbing. Grimmer also suggests testing small areas with different poultices to find which works best.