Advice for Using Bleach to Clean Moldy Surfaces
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Advice on How to Use Bleach When Cleaning Moldy Building Surfaces
Mold Cleaning Mistakes to Avoid when cleaning Mold on Building Framing Lumber or Plywood Sheathing
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Here we describe how to use bleach to clean a moldy building surface and we explain when this cleaning method is useful as well as when it's probably a big mistake. Readers should also see MOLD SPRAYS, SEALANTS, PAINTS for a discussion of other mold killing chemicals and encapsulants.
For more basic mold advice see MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD and also MOLD CLEANING MISTAKES. Our photo at page top shows a moldy home after flooding in Jasper Texas. The drywall and other soft materials needed to be removed, not "sprayed with bleach". But after all demolition and loose debris cleaning, use of a biocide as a final wash is common in this circumstance. What about a small patch of mold on a bathroom wall or ceiling? Here we discuss the use of bleach on moldy surfaces.
GUIDE TO USING BLEACH - Bleach as a "Mold Medicine" to try to kill mold or prevent mold in buildings
Bleach, diluted bleach, or bleach sprays used in cleaning may be appealing but they are unnecessary,
potentially dangerous (if you get bleach in your eyes), and the use of bleach tends to lead to improper and
inadequate cleaning - if you substitute "spraying bleach" for actually cleaning or removing the mold your cleanup will
not be successful.
Our photo (left) shows hard surfaced wall paneling and floor tiles that might be cleaned of light mold contamination using a household cleaner or a dilute bleach solution (described below). But before cleaning mold off of this wall we'd want to know about the wall cavity - if there have been leaks into the wall cavity itself, cleaning the surface alone is probably futile.
The object of mold removal is to clean the surface, to remove loose moldy material, not to try to sterilize the surface. The object of mold remediation is to clean, or remove, the majority of the mold particles
(spores, conidiophores, hyphae, mycelia) from the target surface. Certain mold-contaminated materials that cannot be cleaned (drywall, carpeting, curtains) should be discarded. Clothing and bedding linens or towels can be washed or dry-cleaned.
The operative word to fix in mind is to "clean" or
"remove" the problem mold. "Killing" the mold is not the object - first of all because our lab work shows that you're
unlikely to kill all of the mold on a surface using bleach, unless you use it at a concentration and duration which is so
strong that you're likely to completely destroy the "bleached" material, and second of all because even if you could
"kill" every mold spore, you are at risk of leaving toxic or allergenic particles in place - they may be dead but still
toxic. See MOLD KILLING GUIDE for details.
"Mold removal" by surface scrubbing only works if you're cleaning a relatively hard, non-porous surface such as finished
wood, painted metal, or plastic. Soft materials like Sheetrock™ or drywall which have become moldy generally should be
removed, the exposed surfaces cleaned, and then new drywall can be installed (after you've also corrected the reason for
the mold growth in the first place).
Just spraying or painting-over mold with anything if spraying of fungicides or sealants is to be used in place of actual cleaning or removal of mold
is an improper and inadequate practice which risks leaving a reservoir of toxic or allergenic particles in the building.
Guide for Using Bleach to Clean a Building Surface
If you want to use bleach as a cleaning agent instead of other cleaners (household cleaners, or plain soap and water would work just fine for cleaning a moldy surface) here are some mold cleanup suggestions for homeowners from the Canadian Mortgage and Housing Corporation CMHC. Keep in mind that bleach is a powerful oxidant that is not only dangerous on skin or in eyes, but it will also bleach (whiten) the surface where you're using it, or your clothes or whatever is around if you're sloppy.
Dilute the household bleach with one part household bleach to four parts of clean water (do not add other cleaners to this solution as you may accidentally cause the release dangerous chlorine gas)
Ventilate the work area
Protect yourself: Wear rubber gloves and eye protection
Physically clean loose debris from the surface. Paper towels, rags, stuff you can wipe and throw away are ok, though if you use the same wet moldy rag to wipe everywhere you may be spreading more mold particles than you're removing. We wipe the surface using disposable materials.
Wipe or spray your bleach solution onto the surface: after physically cleaning and removing all loose mold, dirt, debris, from the surface being cleaned,
Bleaching time guide: Let the solution stand on the surface for 10-15 minutes.
Rinse the cleaned surface thoroughly
Dry: Be sure that the cleaned surfaces are totally dry before restoring any building insulation, drywall, etc.
Discard wiping rags, moldy fabrics, moldy drywall, flooded wall to wall carpet and carpet padding, or other similar materials that do not present a hard durable surface and thus cannot be surface-cleaned.
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