A solution for cleaning bricks, comprised of bleach and water, works for most problem areas. For hard-to-remove stains or mildew, trisodium phosphate is a heavy-duty solution to use as a last resort.
To use a bleach solution, combine one cup of bleach with a gallon of water, and use it in conjunction with a scrub brush, whether it is natural or synthetic bristle. Avoid using wire brushes, as they leave traces of steel on the brick, which eventually rusts and discolors the area. Soak the brick thoroughly before applying the solution to keep the brick from absorbing the bleach. If the solution does not work, try a more abrasive solution of trisodium phosphate.
Trisodium phosphate is a last-resort solution that is extremely hazardous. Before making the solution, put on heavy duty rubber gloves and safety goggles. Do not use the solution on any surface other than brick; avoid contact with skin, furniture, flooring or carpeting. To find trisodium phosphate, visit a local home improvement or hardware store. To make the solution, combine a 1/2 cup of trisodium phosphate in a bucket with a gallon of hot water, and dip the scrub brush with coarse bristles into the mixture. Scrub the brick, and then rinse the area with hot water.
For stubborn stains, increase the amount of trisodium phosphate to a cup per gallon of hot water. The solution is extremely abrasive, so remember to be cautious.