Black mould is a serious problem that requires professional treatment. Black mould is a generic name for Stachybotrys chartarum, a strain of mould 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 mould 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 mould 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 mould, according to the CDC. To put it simply, plaster walls provide the perfect breeding ground for black mould. Nevertheless, mould can only grow if the plaster is wet; so as long as you prevent moisture from penetrating your plaster walls, you cannot develop black mould.
Black Mold Appearance
Black mould is not the only type of mould that can grow on plaster. Over 400,000 types of mould exist, and any one of them can grow on plaster walls under the proper conditions. Black mould 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 colour will appear a combination of black and dark green. Even if your mould fits these descriptions perfectly, you still may have a different type of mould, since some non-toxic moulds look similar. Only a mould removal expert can determine the exact mould species.
Black Mold Removal
If a black mould colony has grown inside of a plaster wall, you may need to replace the wallboard completely. Black mould 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 mould. If, however, you notice a small amount of black mould forming on the surface of the plaster, you can stop the colonisation 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 mould with peroxide, vinegar or bleach (diluted with equal parts water) to kill the spores.
- Centers for Disease Control and Prevention: Facts about Stachybotrys Chartarum and Other Molds
- North Dakota State University; Remove Mold for a Healthy Home; Kenneth Hellevang, Ph.D.; April 2009
- University of Missouri Extension; How to Prevent and Remove Mildew -- Home Methods; Wanda Eubank and Betty Feather; April 1998
- Toxic Black Mold Information Center: How to Clean Up a Black Mold Problem