Black mold is a serious problem that requires professional treatment. Black mold is a generic name for Stachybotrys chartarum, a strain of mold that emits dangerous mycotoxins into the air. These toxins can cause severe illness, infection and possibly even cancer, according to the Environmental Protection Agency. Black mold can appear on many household surfaces, including plaster walls.

Plaster and Moisture

Plaster is a porous material. It contains tiny holes through which moisture can become trapped. When moisture becomes trapped, it cannot evaporate, and therefore lingers. Black mold requires constant moisture, according to the Centers for Disease Control, and so it can easily grow on plaster walls that absorb and trap moisture due to high levels of humidity, leakage or flooding. You can avoid this by controlling the humidity in your home with a portable dehumidifier, and by maintaining your plumbing, roof and insulation.

Plaster and Cellulose

Plaster consists of cellulose, an organic compound found in the cells of wood, cotton, plants and plant material. Cellulose materials, like plaster, are especially conducive to the growth of black mold, according to the CDC. To put it simply, plaster walls provide the perfect breeding ground for black mold. Nevertheless, mold can only grow if the plaster is wet; so as long as you prevent moisture from penetrating your plaster walls, you cannot develop black mold.

Black Mold Appearance

Black mold is not the only type of mold that can grow on plaster. Over 400,000 types of mold exist, and any one of them can grow on plaster walls under the proper conditions. Black mold will appear along the plaster wall in a patchy or spotty formation, either velvety or slimy in appearance (depending on whether the colony exists on the surface of the plaster, or deep inside). The color will appear a combination of black and dark green. Even if your mold fits these descriptions perfectly, you still may have a different type of mold, since some non-toxic molds look similar. Only a mold removal expert can determine the exact mold species.

Black Mold Removal

If a black mold colony has grown inside of a plaster wall, you may need to replace the wallboard completely. Black mold can damage the porous material beyond repair if it has had time to breed. In fact, a North Dakota State University report recommends the complete replacement of any wall board affected by black mold. If, however, you notice a small amount of black mold forming on the surface of the plaster, you can stop the colonization by drying the area slowly. Plaster can crack if you dry it too quickly, according to a University of Missouri report. As a result, use fans or heat to slowly remove the moisture, until it disappears completely. Spray black mold with peroxide, vinegar or bleach (diluted with equal parts water) to kill the spores.