Brick may seem virtually maintenance free, but over time dust, soot and other airborne particles can collect on an interior brick wall and dull its colour. Because bricks are porous, grime may even speed up deterioration. For indoor brick walls, the normal solution of power washing isn't practical. Fortunately, it's also not necessary. As long as the bricks and mortar are in good condition, a gentle cleaning is all you need to restore the wall's rich red hue.
Spread a plastic sheet on the floor under the wall. Raise one edge of the sheet up to cover the two lowest rows of bricks. Using waterproof tape, such as painter's tape, attach the drop sheet to the wall. This will catch run-off so it doesn't damage your floor.
Place grease-cutting soap in a bucket with an equal amount of table salt. Add enough water so you can mix the ingredients into a thick paste. Liquid soap is also an option. If you use liquid soap, omit the extra water and add about 10 per cent more salt than soap.
Dip a clean cloth into the paste and spread it on the wall to create a nearly opaque film. With a wire scrub brush, vigorously scrub the paste into the bricks. Let the paste soak in for 10 minutes.
Saturate a clean cloth in pure warm water. Wipe the soap-salt paste off the wall. Rinse the cloth frequently. For a large section of wall or a very dirty wall, change the water when it becomes noticeably dark.
Mix 1 tbsp boric acid in 4.5 litres of warm water. Dip a scrub brush in the solution and scrub the wall with a firm pressure. Let the solution sit for two minutes. Remove the boric acid solution.
Boric acid is not the same as borax. To find boric acid, ask at your local pharmacy.
Before cleaning, check the wall's condition. If any bricks are loose or crumbling or you can scratch the mortar with a key, consult a professional. The wall may require repointing or other repairs to prevent further damage during cleaning.
Wear waterproof gloves and protective glasses when working with boric acid.
Avoid harsh chemicals like muriatic acid (acid wash) or trisodium phosphate unless you know the type of brick you have will tolerate them. These products may discolour some types of brick.