Cleaning Existing Mold Growth

To clean existing mold growth on window surfaces, use a detergent solution and a sponge or nylon brush. It is not necessary to use harsh chemicals such as chlorine, which can potentially damage metal surfaces or carpeting below the window. Detergent is just as effective at removing the accumulated dust on which the mold is feeding. Rubbing alcohol or a diluted chlorine solution can be used in small amounts as a final sterilization of the surfaces after cleaning, however, the sterilization will only be effective until new dust starts to accumulate. If mold growth is present on sheet rock window sills, the same cleaning methods would apply. It make take longer to clean the sheet rock since the texture over the sheet rock is porous. Continuous cleaning may damage the paint, which should be reapplied if necessary.

The mold growth rarely extends below the top surface of the sheet rock sill, and it is not necessary to remove the window sill unless the water damage and mold growth is very extensive such that the sheet rock has become soft and is not structurally sound.

While controlling moisture and mold growth on window surfaces requires some regular maintenance by building occupants and can be inconvenient at times, it is usually only for three or four months during the winter that these steps are necessary. Once temperatures increase outdoors, condensation becomes less of a problem.

If all window sills in a building are cleaned at the beginning of spring, mold growth will typically not return until the next winter. If existing mold growth is not cleaned as summer approaches the mold growth will dry and will be harder to clean later.
While mold growth on window surfaces due to condensation is not a significant problem, mold growth or water staining below window sills or at the base of the wall below a window could be a sign of a larger problem with water intrusion from outdoors. This can potentially lead to more serious mold growth and water damage that may not be initially visible. If mold growth or water damage is observed below the window sills, then additional investigation work should be completed to determine the moisture source so it can be quickly resolved.

It is also important to regularly inspect and maintain the condition of the caulking around the window sill to prevent condensation from entering wall cavities where moisture takes longer to dry, which could lead to more extensive mold growth.
Newer window frames are also designed to drain and have weep holes in the outer portion of the frame. The drain holes in the window tracks should also be checked regularly as part of good housekeeping and maintenance to ensure that debris has not clogged the holes, which could also lead to more significant water damage.

There are various types of installation procedures for windows. They may be flush to the interior wall or be recessed with either a sheet rock or wood sill plate. There may be a drainage mechanism designed into the tracks or if the sills are flush it could cause condensate to run down the outside of the sheet rock on the wall below the window. Regardless of the type of installation, good maintenance and proper care can avoid any water damage or possible mold growth that may occur.