How to Clean Brick Walls
"Can Stain Solver be used to clean a brick house's exterior? Will it harm old brick?"
Stain Solver can be SAFELY used to clean any brick - new or old.
The solution will not harm the brick in any way.
The best way to use it is with a garden hand pump sprayer.
Mix one cup - 8 ounces - of Stain Solver per one gallon of water. Stir till dissolved. If using cool water from a hose, it could take ten minutes of time for the Stain Solver to dissolve with stirring from time to time. If you don't allow the Stain Solver to fully dissolve, the small particles WILL CLOG the tip of the sprayer causing frustration.
Squirt the solution on the DRY brick liberally. A medium mist setting works best. Spray from the bottom of the wall and work UP. It's best to apply the solution to dry brick so it soaks into the brick for deep cleaning.
Work in the shade. Keep the brick wet for at least 15 minutes with the solution. Only work about 150 square feet at a time.
After 15 minutes of soaking time ensuring the solution does not evaporate, lightly scrub the brick for BEST results. Use a brush made to clean RVs on a pole. Rinse the brick well with clear water. When the brick dries, it should look much much better.