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mildew and mold in basement

Bleach applied directly on the mold is the olny thing that will effectively kill all mold and mold spores and eliminate the problem at its source.

A dehumidifier will help and is a good idea in a musty, moldy basement, but it does a better job of PREVENTING mold than killing it. It will "starve" the mold eventually of the humidity it needs to stay alive and grow, and it will eliminate the environement needed for new mold growth, but the spores will survive an the mold will re-grow as soon as the humidity returns. Bleach works quickly and kills the problem at its source.