The Myth.

A myth exists concerning the use and “effectiveness” of chlorine bleach (sodium hypochlorite) in the remediation of a mould problem.

Opposing Views and Confusion.

Chlorine / Laundry bleach is generally perceived to be an “accepted and answer-all” biocide to abate mould in the remediation processes. Well-intentioned recommendations of health departments and other provincal and local agencies are perpetuating that belief. The Environmental Protection Agency  wrote-out/edited their A Brief Guide to Mold, Moisture and Your Home(EPA 402-k-02-003) to exclude their once recommended use of  bleach as a mould clean-up agent.

Does Bleach Really Kill Mold?

Will chlorine bleach kill mould or not—yes or no? The answer is yes, but with a caveat. That answer comes from The Clorox Company, Oakland CA, manufacturer and distributor of Ultra Clorox® Regular Bleach. The company’s correspondence to Spore°Tech Mold Investigations, LLC stated that their Tech Center studies supported by independent laboratories show that “…3/4 cup of Clorox liquid bleach per gallon of water will be effective on hard, non-porous surfaces against… Aspergillus niger and Trichophyton mentagrophytes (Athlete’s Foot Fungus)”. Whether or not chlorine bleach kills other moulds and fungi, the company did not say. The “hard, non-porous surfaces” part of the sentence is a caveat. Mold remediation involves the need to disinfect wood and wood-based building materials, all of which are porous materials. Thus, chlorine bleach should not be used in mould remediation as confirmed by OSHA’s and EPA’s updated recommendations and suggested guidelines. The use of bleach as a mould disinfectant is best left to kitchen and bathroom countertops, tubs and shower glass, etc.

Why Chlorine Bleach is NOT Recommended for Mold Remediation.

Clorine bleach is corrosive and that fact is stated on the product label (not to mention the exposure hazards of dioxins). Yet the properties of chlorine bleach prevent it from “soaking into” wood-based building materials to get at the deeply embedded mycelia (roots) of mould. The object to killing mould is to kill its “roots”.  Reputable mould remediation contractors use appropriate products that effectively disinfect properly scrubbed and cleaned salvageable mould infected wood products. Beware of any mould inspector, mould remediation contractor or other individual that recommends or uses chlorine bleach for mould clean up on wood-based building materials.

Chlorine Bleach Is Active Ingredient in New Mold & Mildew Products.

The appearance of new mould and mildew household products on store shelves is on the rise. Most are dilute solutions of chlorine / laundry bleach. 

Caveat Emptor!

Before purchasing a mould and mildew product, read and fully understand the advertised purpose of that product — and correctly follow the use instructions of a purchased product. The labeling claims on these new products can be confusing — some say their product is a mould and mildew remover while another says their product is a mildew stain remover  and yet others make similar ‘ambiguous’ claims. Make double sure that the product satisfies your intended need on the surface to which it is to be applied. If your intention is to kill mould, make sure the product does exactly that and follow the directions for usage. Consumers may find that mixing their own diluted bleach solution will achieve the same results when used on surfaces recommended by manufacturers of commericial mould and mildew cleaning products — keep in mind that the use of chlorine bleach is not for use on mould infected wood products including wall board, ceiling tiles, wall studs, fabric, paper products, etc.


Chlorine / Laundry bleach is not an effective mould killing agent for wood-based building materials and NOT EFFECTIVE  in the mould remediation process.  The public should be aware, however, that a chlorine bleach solution IS an effective sanitizing product that kills mould on hard non porous surfaces and neutralizes indoor mould allergens that trigger allergies.

CAUTION: DO NOT MIX CHLORINE BLEACH WITH OTHER HOUSEHOLD CLEANING AGENTS. DOING SO CAN CAUSE SERIOUS HARM TO HUMAN HEALTH AND EVEN DEATH. For example, mixing chlorine bleach with cleaning products that contain ammonia or acid (vinegar, as one example) releases chlorine or chloramines, gases which are highly TOXIC.

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