All About Homes Blog

Bleach Doesn't Kill Mold

Monday, January 18, 2010 by Administrator

Good Morning! I hope everyone is having a good new year!

Today I thought I'd talk about bleach and mold! I think the most common homeowner myth I hear out there is that bleach kills mold.

Well, I'm sad to say, that it's just not that simple. Bleach can take the color out of mold/mildew and it can work on totally non-porous surfaces, but it generally won't kill the roots of the mold that grow into any porous material. So, bleaching the mold will make it look like the mold is gone, but if the roots aren't dead it'll come right back. In fact, spraying bleach on porous surfaces will actually foster mold growth because more moisture is added to the material...see below! Who knew!

So here are some more details...

Bleach does not kill mold effectively…ammonia is generally more effective. Check out this website for more info:


  1. Bleach is too diluted and thus too weak to permanently kill mold unless the mold is simply sitting on top of a hard surface like a counter top or sink.
  2. What little killing power chlorine bleach does have is diminished significantly as the bleach sits in warehouses and on grocery store shelves or inside your home or business [50% loss in killing power in just the first 90 days inside a never-opened jug or container]. Chlorine ions constantly escape through the plastic walls of the containers.
  3. Chlorine bleach's ion structure also prevents chlorine from penetrating into porous materials such as dry wall and wood. It just stays on the outside surface, unable to reach mold's enzyme roots, growing inside the porous construction materials. When you spray porous surface molds with bleach, the water in the solution soaks into the wood while the bleach chemical sits on top of the surface, gasses off, and thus only partially kills the surface layer of mold, meanwhile the water penetration of the building materials fosters further mold growth.
  4. Chlorine Bleach is NOT registered with the EPA as a disinfectant to kill mold and it is not recommended by OSHA to kill mold.

So what do you do instead? Well, ammonia is generally thought to do a better job of killing mold roots. Now there are also more environmentally sensitive products as well. If you have a large area of mold, the best thing to do is contact a qualified mold remediation contractor. If anyone recommends using bleach...beware! Here's what the EPA has to say about mold...