Does bleach kill mold?

On a hard surface, mold sits on top. A household cleaner or a diluted bleach solution removes it, and the surface dries. On porous materials, growth reaches into the drywall paper, the wood grain or the carpet backing. Bleach lightens the stain you can see. It does not reach the growth inside, and the water it carries adds moisture to the material. The spot returns, often in the same shape.

The EPA does not recommend biocides such as chlorine bleach as a routine part of mold cleanup. Its guidance is to clean mold off hard surfaces, dry them completely, and replace absorbent materials such as ceiling tiles and carpet that have mold on them. Never mix bleach with ammonia or with other cleaners.

The part bleach never fixes is the moisture. Mold grows where a material stays wet: a slow plumbing leak, a damp basement wall, a roof leak or a bathroom without enough ventilation. If the moisture stays, the mold comes back, whatever you clean it with.

Professional mold remediation works in a different order. Find the moisture source with a moisture meter and a thermal camera. Contain the area with plastic sheeting and negative air. Remove the affected drywall, insulation, carpet and pad. HEPA vacuum the remaining surfaces and apply an antimicrobial treatment. Then dry the structure and confirm it with moisture readings.