Bricks do not support mold growth. As a stone masonry surface, brick has no living nutrients, and since brick is only mildly porous, it does not naturally trap a lot of moisture. As a result, mold lacks the ideal growth conditions that it would find on a drywall panel or a piece of fabric. Though bricks are naturally mold resistant, they are not mold-proof, and it should be noted that mold can develop on bricks under the right conditions.
As living organisms, mold spores require food in order to grow. Mold spores can feed on almost any organic (once-living) material, like fruits, cotton, leaves, soil, wood and paper. Masonry bricks contain no organic materials in their construction, and as a result, mold spores cannot feed on them. Without a source of food, mold spores remain dormant, meaning that they cannot grow, expand or produce the chemicals that they require for their active lifecycle.
In addition to their lack of organic material, bricks do not absorb water. Though mildly porous, bricks lack the absorbent quality necessary to trap water for long periods of time. Without a reliable and continuous source of water, mold spores cannot grow, even if they have the necessary nutrients at their disposal. Overall, a brick wall is one of the most mold-resistant types of wall available, since it has neither the porosity of plaster nor the organic materials found in wood.
Mold Can Still Grow
For all intents and purposes, brick walls do not support mold growth. But even if bricks themselves lack the necessary ingredients for mold, the ingredients -- water and organic material -- can find their way onto brick surfaces. For instance, if a brick wall becomes caked with mud in harsh weather, it now has a source of water and nutrients for mold. Even dust can promote mold growth in large enough amounts, and consistent water on a brick surface can result from very high humidity.
Prevention and Cleanup
Keep your brick wall clean to prevent mold from having the ability to grow. By keeping the wall dirt free, you ensure that it never sustains the necessary nutrients for mold. If mold does grow, wet the entire wall and then spray it with a 50/50 solution of water and vinegar. Scrub the bricks with a wire or plastic brush and rinse the wall.