Back in the day I've heard that bleach is a good way to kill mold. The other day a home inspector suggested that Dawn dish soap actually works much better than bleach. I've heard from another home inspector to use the store-bought mold killer.

Does anyone know what really works and what doesn't for a DIYer?

  • 3
    Both bleach and detergent can kill surface mold. – DA01 Jun 3 '12 at 17:57
  • Bleach will react and become inert after a short period of time and the mold can re-establish. Detergent will stick around a lot longer. Other mold treatments include Sodium Carbonate, TSP, and other salts that make it hard for mold to re-establish especially if things are kept relatively dry. – Paul May 2 '15 at 13:35
  • Yes an home inspector said to clean with dawn then spray with bleach. – user47886 Jan 16 '16 at 16:00

Bleach, when used carefully, may be effective at killing surface mold. However, when I started to research how to get invisible to the eye mold and it's related odor out of some unfinished wood, over and over I kept finding assertions that bleach is inadequate for eliminating mold issues for the following reason:

Mold's hypae (root structures) actually grow into wood and drywall like roots. The hyphae are not killed by bleach because bleach's ion structure prevents chlorine from penetrating into porous materials such as drywall and wood. It stays on the outside surface, whereas mold has protected enzyme roots growing inside the porous construction materials. When you spray porous surface molds with bleach, the water part of the solution soaks into the wood while the bleach chemical sits atop the surface, gasses off, and thus only partially kills the surface layer of mold while the water penetration of the building materials foster further mildew and mold growth. [This quotation appears on many websites almost word for word, but no site I looked at gave any credit to the original source of this information]

How do you get those hyphae out of the wood or other material? You need a surfactants.

Surfactants serve the purpose of significantly lowering the surface tension of water to allow a cleaning solution to penetrate porous surfaces -KleanPros

What's an example of a Surfactant? Dishwashing soap.

This is why some mold cleaning guides will suggest adding dishwashing soap into your bleach/water mixture, or say to skip the bleach entirely, and just use the surfactant cleaning properties to dislodge the mold and remove it from the surface without actually "killing" it.

A mold expert who came to do mold testing at our home claimed that, depending on the species of mold being eradicated, that bleach was the "worst thing you could do" in fixing a mold problem, because it may cause a release of highly toxic mycotoxin particles. Neither the EPA or OSHA recommend bleach for mold removal under "most" circumstances.

The EPA also points out that:

Dead mold may still cause allergic reactions in some people, so it is not enough to simply kill the mold, it must also be removed.

Which goes back to that surfactant thing. If you're talking about a non-porous surface, sure, bleach may work well, so long as you use it properly (ventilate, don't mix with ammonia, etc), but if there's any possibly porous or crevice-filled surfaces, either the dish soap or a epa-registered mold-killing product would be a reasonable choice.

  • 1
    Basically it's always been a three step clean down process. Bleach on the first pass to kill and remove the surface equivalent of mushrooms, rinse with damp towel passes and then take the remainder down with soap solution which you only rinse off later if you're painting. It has to soak into the myceliar component of the fungal growth. Then when you paint, there are anti-mold additives to mix into the paint. And the first pass had better be done as you point out, after educating yourself on what you have. Libraries have some nasty stuff that grows on leather, you don't want to breath it. – Fiasco Labs Feb 2 '14 at 0:49
  • Dispensing with the bleach isn't a bad idea, chlorine isn't something you should be breathing. – Fiasco Labs Feb 2 '14 at 0:51
  • 1
    Be cautious what dishwashing soap you mix with bleach. Some combinations create a chemical reaction that produces toxic vapors. The dishwashing soap should have a statement somewhere on the back label indicating not to mix with bleach, if it is an issue. I usually google to double check even if I don't see it labelled. – AaronLS Oct 31 '17 at 2:16

I've personally found that a spray bottle with a 20% bleach-80% water worked best.

I just find it useful to recap all the information I could find on the web about it and the unanswered questions and hypotheses that still need to be tested. Please feel free to correct and update my answer or by commenting below (Verified information and test result are more than welcome). This answer is a work in process: many things written here need confirmation (cf the (1)) and others would require to ask questions in the stack chemistry (cf the (2))

First: our current technological level isn’t advanced enough to solve that issue. The solutions proposed below are more workaround than anything else. As mold needs moisture, cellulose (it eats it) and air to survive, the most efficient way remains to control humidity (which is unfortunate for those who can’t do it).

Molds are difficult to eradicate because:

  • It can live deeply inside stuff. So only killing the visible mold isn’t enough.

  • Killing all the mold (the visible ones and the one deeply rooted) isn’t enough as the molds generate countless tiny spores (their “seeds”). A single spore can start by itself a whole new mold invasion. The spores are quite tough to destroy (1) and they also float in the air.

So to get rid of mold invasion, several actions seem to be required:

  • 1/ killing the visible mold,
  • 2/ killing the molds deeply rooted inside the wood, wallpaper…
  • 3/ preventing a next invasion: —by making the environment harsh for the molds to grow —by deactivating/killing the spore

Killing the visible mold: it’s easy to do it with bleach, peroxide … (cf the below).

Killing the molds deeply rooted: this is another story as you need something to help the product (which kills the molds) penetrates inside the wood. You need to use a “surfactant”, like dishwashing soap (there is probably more effective one) (1).

1/Preventing (most of?) further invasions:

—By making the environment harsh for the molds to grow: molds seem to be sensitive to pH. Some will be destroyed by an acid pH, but (most) others will be destroyed by the very basic pH (over 9).

—By deactivating/killing the spores: that’s the really difficult part.

Increase the pH: It seems that a basic pH can kill the mold and (and maybe deactivate the spores?). That’s why is used.


Borax (Sodium borate, sodium tetra borate, or disodium tetra borate) is quite basic, so it will Kills/prevent or slow mold growth. (Most, but not all types of molds needs acidic environment). 1 tablespoon in warm water (about 40 °C—makes it easier to dissolve it)

According to many sources, Borax was effective and durable but some concerns have been raised about its effect on health (especially when ingested or when in contact with eyes). If I understood well, it was widely used for everything and anything without any concern about its potential toxicity (it’s also not biodegradable). So in results, it has been “classified” by European Commission as a potential threat (fertility issue, among others).

As borax become difficult to find (in the EU) I was wondering if any strong basic solution could do the job. What about for instance a solution containing (cheap) dishwasher powder (2)?

“Borax Substitute”: sodium sesquicarbonate is much easier to find (in the EU) than Borax but is it really as efficient? And what about its durability (unlike borax, it’s biodegradable) (2)?


Others:

—Concrobium Mold Control: this product also plays on the pH to remove molds. It contains sodium bicarbonate (baking soda, pH=9), sodium carbonate (washing soda, pH=12) and trisodium phosphate (TSP, pH=12). Is TSP use only to increase the pH or for other reasons (2)?

—Sodium Bicarbonate: its pH is lower than Borax so it seems to be less effective (in my case, this solution did slow a bit the process, but not much). But it’s safe.

—Sodium per carbonate: (2) —Trisodium phosphate (TSP): (called “borax substitute”). Does it work despite its biodegradability? (2)

—The sealing solution (seems to be the most effective): Clean up the mold from the support, wait long enough to dry it, and then “vitrify” the support (using for instance any transparent basic flooring product). The mold won’t come back on it since a thin layer of “plastic” protect its food (cellulose) against it. As for the mold that has been sealed under the layer, it’s not clear what will happen. What would happen to a mold simply recovered with a thin layer of PU or wax. But it will protect from the spores which are the main health issue. (2)?

2/Killing the Mold:

  • Bleach: kill the visible mold (how? (2)) but the chlorine doesn’t penetrate into the wood, wallpaper so it doesn’t kill the molds deeply rooted. The water contained in the bleach will penetrate in the wood so that will help the ‘inside’ molds to grow faster.

  • Hydrogen peroxide: same as bleach, but safer (no toxic gas) By changing the pH: Acidic solution (Vinegar…): might kill the mold that needs basic ever. Basic solution (baking soda, borax…) might kill molds that need acid ever.

  • What work (a little) for me: mix some hot water with borax, then add 30-50% of bleach, and some dishwashing soap. Remove the mold with a sponge.

3/Killing/deactivating the spore:

Since spores can float in the air, some recommended using Chlorine Dioxide: it’s a gas which kills (deactivates) the spores (of most species). The gas is unstable and explosive from a certain concentration so you won’t find it in your supermarket. But it’s easy to make ("providing you find sodium chloride". I’m still looking for that…). You only need to mix a drop of sodium chlorite with a drop from any acid (e.i: citric acid). When the two drops meet, the gas is produced. It’s best to evacuate the building during the process (they recommend 48h). (You can find on eBay devices measuring the concentration of this gas.). Some hospital uses it.

In brief, many questions remain. We are still waiting for THE scientific invention to deal with that (a gene therapy?)

(3) The PU coating DIY technic is easy: just missed some PU expansive foam with acetone to get PU a water-like substance that could PU coat stuff (11 gr/100 ml works well for camping gears too, it’s not hydrophilic and waterproof, but ‘breathable’). But watch for the isocyanate: it can penetrate your skin: latex gloves should probably OK for 10 minutes, but no more (or use a PP plastic bag as gloves).

Sources:

http://removemoldguide.com/do-it-yourself/remove-mold-from-wood/

https://chemistry.stackexchange.com/questions/347/why-are-the-majority-of-cleaning-solutions-basic

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1214660/

  • spent quite some time to share these info, to get down-voted. Why? – JinSnow Jan 13 '17 at 15:44
  • Not the downvoter, but length of time spent on answer does not directly correlate with quality of answer – Tom Busby Mar 6 '17 at 11:09
  • @TomBusby I agree. But concerning the down-vote you justified by your comment, I would say it reflects the average stack user's way to use the downvote button. – JinSnow Mar 6 '17 at 12:05
  • @JinSnow, stumbled across your post a year later. I suspect the downvote was for this reason. Answers are intended to be definitive solutions. You've got a lot of information here, but it mostly duplicates other answers and much of the supplemental information is worded as speculative, even adding new questions. You added some general reading sources at the end, but not tied to specific facts. It might have received a better reception if you had limited it to just what you know for sure (citations), and left off your own unanswered questions and anything speculative. – fixer1234 Feb 4 at 23:55
  • 1
    @TomBusby "Answers are intended to be definitive solutions", no. Answer are intended to bring the most useful information. In most case there is no permanent answer, solutions are constantly evolving. "Not tied to specific facts", well, only "known alternative to get rid of mold". Some people join stack to rule it and impose their views, others to share information. You'd better invest your time in proposing better answer than downvoting/wasting time of people who invest their time to share. – JinSnow Feb 6 at 8:45

If you have a serious mold problem in your home, get a professional to treat it. No home remedy is going to help in that case.

TSP has essentially been taken off of the market. It was used often to prep for painting in the past. There are TSP substitutes, but this stuff is dangerous.

My allergist recommended cleaning with white vinegar solution to remove/control mold in the home on a regular basis in the bathroom, refrigerator, etc.

Borax is still readily available. You can find it in the grocery in the laundry detergent aisle. As for it causing inhalation injuries, don't snort it. Sheesh, everything is dangerous if not used properly/according to directions. I use borax with every load of laundry I do. It is a great, inexpensive laundry booster and cleaning agent.

Someone was asking/hoping they could get their hands on some "sodium chloride." Look in your kitchen cabinet.... it's table salt.

  • If you have a mold problem in your house, you have a water problem in your house. Fix the water problem, or the mold will just keep turning up over and over again. – ThreePhaseEel Mar 5 '17 at 22:44

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