Bleach Does NOT "Kill" Mold
Updated: Jan 12
D. Douglas Hoffman Executive Director of NORMI - NORMI.org
A well-known expert in our area, when interviewed on a local New Orleans radio station, recently said, “When you have a mold problem, simply wash down the affected area with diluted bleach.” We have seen FEMA handing out gallons of Clorox to flood-victims. Lowe’s and Home Depot stock up pallets of the stuff whenever the impending doom of a threatening hurricane is close. This is one of the most widely publicized “urban legends”. Bleach is a powerful oxidizer and can, in many instances, sanitize surfaces of certain types of bacteria but when you are faced with a wall covered in mold, bleach is NOT the product to use.
Eyebrows raise in disbelief every time I say the phrase “bleach doesn’t kill mold.” Some look at me as if I’m speaking another language and they are right. I am speaking the TRUTH. Bleach (active ingredient is Sodium Hypochlorite) is very effective in removing the discoloration but may leave the microflora that will enable the mold to return in exactly the same spot when conditions are right. So, “how do you know this,” I’m asked.
Several years ago we helped develop a process by which shingle and tile roofing systems could be cleaned of the mold and mildew that plague them. Look at any Real Estate guide or website that lists houses for sale and you’ll see house after house with mold streaks running down from top to bottom of the roofing system. The mold on the roof looks ugly but that was not our biggest concern.
There are two bigger concerns and, therefore, reasons to address this roof mold problem. 1) It destroys the shingle and, 2) it makes your air conditioning system less efficient. First, shingles are made, primarily, of organic materials. The asphalt or fiberglass content in a shingle is only a small percentage of the entire composite. This organic material is ripe fruit for the mold to eat. As we all know, mold needs to have a nutrient of some sort and organic materials are especially appealing. The petroleum-based asphalt is protected from the UV light of the day’s sun by a “ballast” or granules that are “glued” to the surface of the shingle. When the mold begins to grow it “pops” the granules off of the shingle exposing the asphalt to the UV, thus shortening the life of the shingle. When shingles begin to curl, that’s a good sign that the shingle is drying out and its life is ending. Cleaning the roof off using an effective biocide will lengthen the life of the shingle by allowing the granules to remain tightly adhered to the surface.
Secondly, a black roof absorbs more heat than a lighter roof. Interestingly enough, in Florida, most homeowners choose a lighter roofing color for that very reason and yet, after a few years, they all end up the same color – black. We commissioned a study once in conjunction with the University of South Florida and found a substantial difference in attic temperatures once the roof was cleaned and the original lighter color was restored. I mean 30 degrees or more. That means by simply cleaning your roof to the lighter color you could make a major difference in the attic temperature and that would allow your air conditioning system to function more efficiently. In most cases the attic is the insulating space just above the air conditioned space so having those temperatures reduced substantially lowered the air conditioning bill.
The importance of understanding these problems make it relatively easy to sell the customer of the value of having their roof cleaned. However, what product or products to use could make a substantial difference in the longevity of the cleaning process and the effect of the cleaning process on the roofing system. Of course any time of high pressure wash could destroy the shingle by removing the granules so a low pressure wash is desirable and that makes the chemical solution you use more important. We used a combination of surfactants, detergents, and BLEACH (sodium hypochlorite) to lightly spray on the roof then rinse it off with no more pressure than a garden hose. It worked great. Only problems were that the landscaping had to be protected from the toxicity of Clorox and the mold would return in less than two years. Even walking around on the roof every couple of years could damage the roofing system so we looked for a better alternative.
Anecdotally, my wife wonders why she has to clean the same spot of mold on the bathroom tile month after month. Now she knows why. The mold has never been killed – it simply goes clear and then returns. Bleach will not kill the mold but a good biocide, or anti-microbial, will.
To underscore the validity of my claim, I suggest the “Journal of Forest Products” who commissioned a study by Oregon State University a couple of years ago. We have this article on our website where we have posted the abstract and the results. The “implications” of their testing showed exactly what we have been training for years. The stain disappears but the microflora remains and under the right conditions the mold will begin to grow.
In our Sanitization Protocol we recommend using GREEN technologies to remove surface mold. When you use the right kind of anti-microbial, the mold will be destroyed and the underlying bio-slime will be annihilated. I wish we had known about these kinds of technologies ten years ago when we were cleaning roofing systems. Instead of spending so much time protecting the landscape, we could have done an additional job or two. We could have completed more jobs and our subsequent warranty workload would have been reduced.