You may have heard that the best way to kill black mold (Stachybotrys chartarum) is to douse it with bleach, but that's only true when it's growing on nonporous surfaces. The Environmental Protection Agency and the Occupational Safety and Health Administration both recommend scrubbing active mold colonies with soap and water to remove them from porous surfaces, including wood, drywall, concrete and tile grout. Depriving mold of the moisture it needs to survive by fixing leaks and controlling indoor humidity is the most effective way to control it.
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Use Bleach for Nonporous Surfaces
Household bleach is a strong disinfectant, and it does kill mold on contact. It's corrosive, though, so it can end up doing more harm than good. Moreover, it has a high surface tension that prevents it from penetrating porous materials, such as wood or concrete. The mold on the surface may die, but the roots stay alive, and the mold can grow back.
Bleach can dull metal finishes, so it isn't the best cleaner for chrome or brass faucets, trim or decorative features. It does make sense, however, to use bleach to remove mold from such surfaces as:
- Plastic laminate, Corian ® or cultured marble countertops
- Fiberglass bathtubs or shower stalls
- Vinyl or PVC trim
- Porcelain bathroom fixtures.
It's never a good idea to use bleach full strength. Instead, dilute it. The Centers for Disease Control recommends mixing no more than 1 cup of bleach per gallon of water. When bleach is included as an ingredient in commercial cleaners, it is already sufficiently diluted, so it's safe to use these cleaners according to directions.
Do not mix bleach with ammonia. When combined, they produce a toxic gas.
Use Soapy Water for Porous Surfaces
Detergent and water are all you need to clean black mold from most porous surfaces, such as wood, brick and stone. Before you scrub, it's a good idea to vacuum away as much loose material as you can, but before you do this, spray the mold with water to prevent spores from flying around while you're vacuuming.
Wear gloves and a respirator while scrubbing, and be sure to change the water often. As a rule of thumb, you should change the water when it becomes the same color as the mold.
Let the surface dry completely after scrubbing, and then give it a final vacuuming with a HEPA vacuum cleaner. Wear a respirator, and make sure the heating/cooling ventilation system is off to prevent spores from circulating into other rooms.
Once black mold has taken root in certain materials, it's virtually impossible to remove it, and the materials should be discarded. This is true for drywall, most types of carpeting and padding, and fiberglass or cellulose insulation.
Prevent Black Mold from Growing
Black mold is just one of thousands of mold species that can grow inside a house. Like all species, it goes dormant when it doesn't have moisture, and it can return to life as soon as moisture becomes available. The key to keeping it at bay, therefore, is to keep things dry.
Fix Leaks: A spot of mold on a wall is often the sign of a plumbing or roof leak. Before cleaning the mold, it's important to fix the leak, or the mold will quickly return.
Control Humidity: Mold often grows in the bathroom, basement and other rooms that have poor lighting and ventilation. It's important to physically remove it, but it's just as important to lower the humidity and prevent condensation. You can do this by opening a window or running a fan to improve air circulation. It also helps to run the air conditioner, which is essentially the same as running a dehumidifier. In winter, it may also help to run a heater in problem areas to promote evaporation.
Wipe Off Condensation: Interior window frames and sills are breeding grounds for mold, because the sharp temperature differential at a window makes condensation almost inevitable, especially in winter. On cold days, it may be impractical to run a fan or open a window to improve air circulation, so the next best strategy is to wipe off condensation periodically with a rag.
A Natural Mold Killer
You can make an effective mold-killing spray using a few different methods. Using vinegar and borax, mix a cup of borax in a gallon of water, and then add a cup of vinegar. This solution kills mold on contact, whether you spray it or use it as a scrubbing solution. Tea tree oil or even vodka are also effective ingredients to try when killing mold.
Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker and Family Handyman.