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.
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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.
GUIDE TO USING BLEACH - Bleach as a "Mold Medicine" to try to kill mold or prevent mold in buildings
Bleaching 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
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.
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 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.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
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  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.) .
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. 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. 
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. 
Ask a Question or Search InspectApedia
Questions & answers or comments about using bleach to "kill mold" or as a building surface cleaner or disinfectant.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
 Manzanera, M., S. Vilchez, and A. Tunnacliffe, "Plastic Encapsulation of Stabilized Escherichia coli and Pseudomonas putida", Applied and Environmental Microbiology, Appl. Environ. Microbiol. May 2004 vol. 70 no. 5 3143-3145, American Society for Microbiology, Abstract:
Escherichia coli and Pseudomonas putida dried in hydroxyectoine or trehalose are shown to be highly resistant to the organic solvents chloroform and acetone, and consequently, they can be encapsulated in a viable form in solid plastic materials. Bacteria are recovered by rehydration after physical disruption of the plastic. P. putida incorporated into a plastic coating of maize seeds was shown to colonize roots efficiently after germination.
 Leung W.K., A.P.S. Lau, K.L. Yeung, "Bactericidal and sporicidal performance of a polymer-encapsulated chlorine dioxide-coated surface", Journal of Applied Microbiology, Volume 106, Issue 5, pages 1463–1472, May 2009.
Canter, D.A., Gunning, D., Rodgers, P., O’Connor, L., Traunero, C. and Kempter, C.J. (2005) Remediation of Bacillus anthracis contamination in the U.S. Department of Justice mail facility. Biosecur Bioterror 3, 119–127.
Callerame, J. (1989) Process for the production of chlorine dioxide. US Patent 4877500, US Patent and Trademark Office.
Gordon, G. and Rosenblatt, A.A. (2005) Chlorine dioxide: the current state of the art. Ozone Sci Eng 27, 203–207.
McDonnel, G. and Russell, D. (1999) Antiseptics and disinfectants: activity, action and resistance. Clin Microbiol Rev 12, 147–179.
Huang, J., Wang, L., Ren, N. and Ma, F. (1997) Disinfection effect of chlorine dioxide on bacteria in water. Water Res 31, 607–613.
Ogata, N. (2007) Denaturation of protein by chlorine dioxide: oxidative modification of tryptophan and tyrosine residues. Biochemistry 46, 4898–4911.
Simonet, J. and Gantzer, C. (2006) Degradation of the Poliovirus 1 genome by chlorine dioxide. J Appl Microbiol 100, 862–870.
Sy, K.V., Murray, M.B., Harrison, M.D. and Beuchat, L.R. (2005) Evaluation of gaseous chlorine dioxide as a sanitizer for killing Salmonella, Escherichia coli O157 : H7, Listeria monocytogenes, and yeasts and molds on fresh and fresh–cut produce. J Food Prot 68, 1176–1187.
Young, S.B. and Setlow, P. (2003) Mechanisms of killing of Bacillus subtilis spores by hypochlorite and chlorine dioxide. J Appl Microbiol 95, 54–67.
Wang, X.W., Li, J.S., Jin, M., Zhen, B., Kong, Q.X., Song, N., Xiao, W.J., Yin, J. et al. (2005) Study on the resistance of severe acute respiratory syndrome-associated coronavirus. J Virol Methods 126, 171–177.
 W A Rutala and D J Weber, "Uses of inorganic hypochlorite (bleach) in health-care facilities.", Clin. Microbiol. Rev. October 1997 vol. 10 no. 4 597-610 - Summary:
Hypochlorite has been used as a disinfectant for more than 100 years. It has many of the properties of an ideal disinfectant, including a broad antimicrobial activity, rapid bactericidal action, reasonable persistence in treated potable water, ease of use, solubility in water, relative stability, relative nontoxicity at use concentrations, no poisonous residuals, no color, no staining, and low cost. The active species is undissociated hypochlorous acid (HOCl). Hypochlorites are lethal to most microbes, although viruses and vegetative bacteria are more susceptible than endospore-forming bacteria, fungi, and protozoa. Activity is reduced by the presence of heavy metal ions, a biofilm, organic material, low temperature, low pH, or UV radiation. Clinical uses in health-care facilities include hyperchlorination of potable water to prevent Legionella colonization, chlorination of water distribution systems used in hemodialysis centers, cleaning of environmental surfaces, disinfection of laundry, local use to decontaminate blood spills, disinfection of equipment, decontamination of medical waste prior to disposal, and dental therapy. Despite the increasing availability of other disinfectants, hypochlorites continue to find wide use in hospitals.
 Carole A. Parnes, "Efficacy of Sodium Hypochlorite Bleach and "Alternative" Products in Preventing Transfer of Bacteria to and from Inanimate Surfaces", Journal of Environmental Health, Vol. 59, 1997 - Introduction:
The use of environmentally "safe" products or "home mixtures" as alternatives for commercial products specifically manufactured for various home cleaning/disinfecting chores continues to be advocated in newspaper and magazine articles, in books, by environmental groups, and even by government agencies (Household Hazardous Waste Projects). By 1993, at least 35 states had issued guidebooks recommending the use of alternative products (1). Major reasons given by consumers for use of alternative products are: improving the environment, reducing hazards, reducing water pollution, and cost savings. At a recent environmental conference (October 1995), one participant, the author of a book recommending the use of alternative products, suggested that if one "uses fewer toxic chemicals," one's "lifestyle is healthier" and the use of "naturally sustainable ingredients" is better for the environment (2,3). However, unlike commercial products, "alternatives" and "home mixtures" are not controlled by federal safety regulations and have no precautionary labeling. They have no directions for use, nor for proper disposal. The preparations may be chemically unstable, and may degrade in the container in which they are stored. It is highly unlikely that the "alternatives" have been evaluated for environmental safety or compatibility, and they have not been registered by the Environmental Protection Agency as disinfectants.
[TABULAR DATA FOR TABLE 1 OMITTED]
Alternative products are usually recommended for cleaning kitchen and bathroom surfaces and glass, but some are suggested for disinfecting (4,5,6,7), without mention of anti-microbial efficacy. The object of disinfection is to reduce the spread of infection and disease by eliminating the causal organisms. Mechanical removal of organisms from any surface is important; however, if removal is not combined with disinfection, or if the organisms are removed from one surface only to be deposited onto another, the process has not been successful. Several studies have shown the role of surfaces in households, day care centers, and various institutions in the transmission of bacterial and viral diseases (8,9,10,11).
Two recent studies conducted to determine the antimicrobial activity of alternative products have shown that they may not be as effective as proclaimed by their advocates. A study at the University of Minnesota indicated the lack of antimicrobial efficacy of various alternative products on a plastic laminate surface in the presence of bathroom and kitchen soils (12). The "alternatives" used in these tests included those most commonly recommended for cleaning and for disinfection: ammonia, baking soda, borax, lemon juice, and vinegar. A commercial disinfectant containing bleach also was tested. The undiluted disinfectant and vinegar were most effective in reducing the number of organisms on the surfaces. The remaining alternative products showed little efficacy. No attempts were made to determine the number of viable organisms remaining on the sponges used to clean the surfaces.
Bauer et al. also utilized a single test surface (Formica[R]), which after being inoculated with bacteria, was sprayed with the test product solutions and then wiped with dampened sponges (13). Ammonia, borax, baking soda, vinegar and one commercial antimicrobial spray product were evaluated. These tests showed that only the antimicrobial product significantly reduced the number of viable organisms on the Formica[R] surface and on the sponges. None of the "alternatives" showed efficacy in either the Association of Official Analytical Chemists (AOAC) Use Dilution Test (which is required by the EPA to verify efficacy of dilutable products as disinfectants) or the EPA Non-Food Contact Sanitizer Test (in which a 3 log reduction in the number of contaminating organisms demonstrates efficacy as a sanitizer).
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home",
U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
US EPA - Mold Remediation in Schools and Commercial Building [ copy on file as /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [on file as /sickhouse/EPA_Moho_Guia_sp.pdf - - en Espanol
Allergies, Allergens, Allergy Testing in buildings - References & Products
"IgG Food Allergy Testing by ELISA/EIA, What do they really tell us?" Sheryl B. Miller, MT (ASCP), PhD, Clinical Laboratory Director, Bastyr University Natural Health Clinic - ELISA testing accuracy: Here is an example of Miller's critique of ELISA
http://www.betterhealthusa.com/public/282.cfm - Townsend Letter for Doctors and Patients
The critique included in that article raises compelling questions about IgG testing assays, which prompts our interest in actually screening for the presence of high levels of particles that could carry allergens - dog dander or cat dander in the case at hand.
http://www.tldp.com/issue/174/IgG%20Food%20Allergy.html contains similar criticism in another venue but interestingly by the same author, Sheryl Miller. Sheryl Miller, MT (ASCP), PhD, is an Immunologist and Associate Professor of Basic and Medical Sciences at Bastyr University in Bothell, Washington. She is also the Laboratory Director of the Bastyr Natural Health Clinic Laboratory.
Allergens: Testing for the level of exposure to animal allergens is discussed at http://www.animalhealthchannel.com/animalallergy/diagnosis.shtml (lab animal exposure study is interesting because it involves a higher exposure level in some cases
Allergens: WebMD discusses allergy tests for humans at webmd.com/allergies/allergy-tests
Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon)
"Disease Prevention in Home Vegetable Gardens,"
Department of Plant Microbiology and Pathology,
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
US EPA: Una Breva Guia a Moho - Hongo [on file as /sickhouse/EPA_Moho_Guia_sp.pdf - - en Espanol
OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold
Mold or allergens may not be the only or even the main indoor environmental contaminant. Don't let media attention to mold
cause so much enviro-scare fear that other, possibly more urgent hazards go un-addressed.
Rodents, Mice, Squirrel Control - I find high levels of mouse and rodent dander, fecal dust, and urine-contaminated dust in some buildings,
and high levels of these materials in building insulation in those locations. If you have a mouse problem, particularly if mice and their waste (fecals or urine) are contaminating
the building HVAC or building insulation, may need both steps to clean up or remove infected materials and steps to stop an ongoing
rodent problem. If squirrels are a problem, the cleanup needs to include closing off entry openings into the building. Get some
help from a licensed pest control expert.
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The HOME REFERENCE BOOK - the ENCYCLOPEDIA of HOMES, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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