Pre-Cleanup moldy basement framing Advice for Using Bleach to Disinfect Building Surfaces or to Clean Moldy Surfaces

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Bleach to kill mold? Bleach to remove stains? Bleach to disinfect surfaces or water?

This article explains the usual bleach solution used to clean or disinfect building surfaces and we describe how to use bleach to clean a moldy building surface. We explain when the standard bleach solution cleaning method is useful as well as when it's probably a big mistake.

Find here: 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. Links to explanations of how to use bleach to disinfect water or a well.

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Guide for Using Bleach to Clean a Building Surface

Household cleaners (C) Daniel FriedmanIf 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.

Watch out: 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.

Using Bleach to clean, to disinfect, or to kill mold in buildings - Warning!

Moldy paneling and flooring (C) Daniel FriedmanBleaching mold in an effort to kill it, while psychologically understandable, is n ot the proper nor recommended approach to getting rid of a mold problem.

Here we explain why bleach may be satisfying, maybe even useful for cosmetic reasons, but it's not the right approach to mold remediation.

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.

Our photo at left shows an area for further mold investigation in a basement: the cavity side of paneling in an area that has been damp or wet.

[Click to enlarge any image]

What about a small patch of mold on a bathroom wall or ceiling? This article explains the use of bleach on moldy surfaces.

Reasons Why Bleaching Mold is a Mistaken Approach to Mold Cleanup

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.

Using Bleach as a Water Disinfectant or to Shock a Well

How Bleach Works: Information about disinfectants & contamination cleanup procedures

How does bleach remove stains?

Household bleach is a mixture of sodium hypochlorite (0.5%) and mostly water (99.5%).

It's the sodium hypochlorite that's the active ingredient in bleach. Bleach is an oxidizing and a bleaching agent and a disinfectant. - Grant and Hackh's Chemical Dictionary, 5th ed.

The chemical formula for sodium hypochlorite is NaClO - or sodium (Na or salt), Chlorine (Cl) and Oxygen (O). In NaClO the chlorie atoms are very reactive, snagging electrons from other nearby molecules. Nearby hydrocarbons that comprise organic materials (mold) and stains (maybe dirt or food) give up electrons to the chlorine while the oxygen and chloride molecules in the bleach stick to the carbons.

Those modified carbon molecules are changed by their new passenge molecules to become highly soluble in water. Water, then, can flush those molecules away - removing the stains. Because the stain particles, now water soluble and now washed away, are physically removed from their original spot, the stain material is actually "gone" - in a favorable reaction.

How does bleach disinfect surfaces, materials, or water?

Bleach is also a really good oxidizer. Its easily-freed oxygen molecule oxidizes molecules that comprise bacteria, fungal spores (or "mold"), other organic materials (fungal hyphae or structures), and even viruses, or cells within those organisms, thus "killing" them.

The effectiveness of bleaching anything depends on the concentration of bleach and its exposure time. Higher concentrations and longer exposure increase the "kill rate" of bleach when attacking organisms.

Disinfecting water or surfaces does not necessarily physically "remove" the harmful pathogens being treated. Rather, it "kills" them.

Unlike "stain removal using bleach", to disinfect a material or surface you should first clean the surface to remove as much debris and dirt as you can.

To use bleach to disinfect dishes

For example, to disinfect dishes (not something that is normally necessary) you would first was them, then use two teaspoons of household bleach in one gallon of clean water to make a disinfecting soak. Immerse your dishes for two minutes or longer in this solutin, then drain the dishes and let them dry in the air. Don't wipe the "disinfected" dishes with your dishcloth as you'll probably be re-infecting them.

To use bleach to kill germs on surfaces

To disinfect a surface like the surface in your microbiology laboratory, use a mixture of household bleach and clean water in a ratio of 1:9, that is 1 part bleach to 9 parts water. This disinfecting solution remains usable for about 24 hours.

On very dirty surfaces such as the basement floor after you've cleaned up a sewage spill and washed the floor with detergents and rinsed it clean, you'd need a 20% solution of bleach - 1 part bleach to 4 parts clean water. That's because the high level of organics tend to neutralize the bleach by rapidly absorbing its chlorine and oxygen.

Watch out: from both field and lab experience I [DF] emphasize that bleach on very soiled, very infected, or very moldy building surfaces is not likely to kill every single organism - you would have to leave such highly-concentrated bleach on a building surface or material for so long to kill 100% of the organisms on the surface that you're likely to also oxidize and destroy the material itself.

Watch out also: do not use a stronger concentration of bleach than necessary. Aside from the safety hazards and the risks of damaging the bleached material I already cited, excessive bleach concentration (with less water) can actually make the solution less effective at disinfecting or at removing stains. Household bleach from the bottle should always be diluted with water before using ti.

Anyone (including myself) has ever experimented with over-dosing bleach on a pair of jeans only to find out that the newly-bleached jeans fell apart will know what I mean.

Bleach Concentrations to Use

Uses of Bleach Discussed at


Continue reading at MOLD CLEANUP - MISTAKES to AVOID or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.





Or see SIDING, WOOD CLEANERS, STAINS, PAINTS - separate article on how to remove stains on siding & how to choose the proper paint or stain coating

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