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

  • MOLD CLEANUP, BLEACH - CONTENTS: Advice on using bleach solution to disinfect or clean building surfaces. 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.
  • POST a QUESTION or READ FAQs about using bleach to "kill mold" or as a building surface cleaner or disinfectant

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Bleach to kill mold? 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.

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GUIDE TO USING BLEACH - Bleach as a "Mold Medicine" to try to kill mold or prevent mold in buildings

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.

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.

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.

Using Bleach as a Water Disinfectant or to Shock a Well

  • The procedure for "shocking" a drinking water well to disinfect it as part of well servicing, repairs, or in response to bacterial contamination, is described in detail at WELL CHLORINATION & SHOCKING
  • The procedure for using bleach to disinfect water for drinking purposes, such as emergency purification of water in the field or following floods or storms, is described in detail at CHLORINE DISINFECTANT for Drinking Water.

More Information about disinfectants & contamination cleanup procedures

  • At DISINFECTANTS & SANITIZERS, SOURCES we list suppliers of biocides, fungicidal sealants, and related mold sprays and sewage backup cleanup products.
  • At MOLD CLEANERS - WHAT TO USE we describe the basics of how to clean off moldy building surfaces and what simple products to use.
  • At MOLD SPRAYS, SEALANTS, PAINTS we provide a guide to buying and using fungicidal sprays and sealants, we describe mistakes in use of mold sprays, and we define biocide, disinfectant, sanitizer and related terms.
  • At FUNGICIDAL SPRAY & SEALANT USE GUIDE we provide a Guide to Use of Fungicidal Sealants on Wood Building Materials
  • At SEWAGE CLEANUP STANDARDS we include details of how to mix & use bleach & other disinfectants or sanitizers for building cleaning & disinfection



Continue reading at MOLD CLEANUP - MISTAKES to AVOID or select a topic from the More Reading links shown below.




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MOLD CLEANUP, BLEACH at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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Frequently Asked Questions (FAQs) about using bleach as a household cleaner, for mold cleanup, in wells as a water disinfectant, etc.

Question: I heard that using bleach straight will encapsulate the bacteria or virus

Dear friends, first of all I love your web site. It must have been a real labor of love to build. Good job. I was told a while back that one must dilute household bleach for it to disinfect a surface. I heard that by using it straight it will encapsulate the bacteria/virus’ you are trying to clean. Would you know if this is true? Thank you very much for your time. B.S., Sparrow Bush NY

Reply: Nonsense. There are different reasons for diluting bleach but not the one you offer. But indeed some encapsulated pathogens such as Staphylococcus aureus are resistant to bleach disinfectants, diluted or in higher concentrations.

Bleach (hypochlorite) has been used as an effective disinfectant for more than 100 years [3] and interestingly some "environmentally safe" and "home remedies" used as alternatives are not government controlled and may be significantly less effective. (Ammonia, borax, baking soda, vinegar and one commercial antimicrobial spray product were evaluated.) [4].

We can find absolutely no basis for the claim that undiluted household bleach "encapsulates" and thus fails to treat bacteria or viral contaminants when used "full strength" as a cleaner, but there is a different reason that household bleach (laundry bleach) is diluted before use: out of the bottle, household bleach is strong enough to damage many surfaces and materials (as well as your eyes and skin) and used full strength it is also a bit difficult to rinse clean. That's the reason that for typical household cleaning uses bleach is diluted 1 part bleach to 4 parts water.

The term "encapsulation of bacteria" is, however, a real one and has been discussed among microbiologists in explaining why it is difficult to treat these pathogens in certain circumstances - but not household cleaning. [1]That may be where some confusion has arisen.

Bleach as an oxidizing biocide, at normal household cleaning dilutions, is common, widely used, safe, and effective against many pathogens.

The oxidizing biocide, ClO2, is a common disinfectant. It is safe (McDonnel and Russell 1999) and effective against a broad spectrum of bacteria, spores and viruses over a wide pH range from 2 to 8 (Huang et al. 1997; Young and Setlow 2003; Sy et al. 2005; Simonet and Gantzer 2006). The disinfection ability of ClO2 has also been reported for B. anthrax cells and spores (Canter et al. 2005), the severe acute respiratory syndrome-associated coronavirus (Wang et al. 2005) and the influenza A virus (H1N1) (Ogata and Shibata 2005).

ClO2 is a very reactive free radical molecule. Owing to its unique one-electron transfer reaction mechanism, it is also a highly selective oxidant (Gordon and Rosenblatt 2005). It attacks electron-rich centres in organic molecules (Gordon and Rosenblatt 2005) and kills micro-organisms through oxidizing their cell membranes (Berg et al. 1986) and denaturing their proteins (Ogata 2007). It breaks the inner membrane of spores preventing their proper germination (Young and Setlow 2003) and reacts with the viral envelope to cause irreparable damage and inactivation (Ogata and Shibata 2005).

ClO2 solution can be applied or sprayed directly onto the target surface for action. The disinfection ability, however, diminishes with time in terms of minutes as the ClO2 vaporizes. In enabling a longer lasting disinfection performance, ClO2 gas was generated from sodium chlorite salts stored in a polymer matrix through a reaction with an acid (Callerame 1989; Wellinghoff 1997), and the acid was either stored with the salt or formed as byproduct of polymer decomposition. This process is inevitably slow as the generation of ClO2 gas depends on the release or production of acid and its subsequent reaction with sodium chlorite. [2]

It is the case, however, that some pathogens such as Staphylococcus aureusare are indeed resistant to simple bleach as a disinfectant. Diluting or not-diluting the bleach is not pertinent to that problem nor its solution.

Staphylococcus aureus was the least susceptible to ClO2 among the tested vegetative species. Staphylococcus aureus also exhibited similar low susceptibility to a hypochlorite (i.e. bleach) solution (data not shown). This may be related to the presence of carotenoid pigments in Staph. aureus that are antioxidative and provide the bacteria with some degree of protection from oxidizing biocides. [2]


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