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How to Treat a Mold Infestation on Wood With Borax 20 Mule Team Powder

Maren is a fixer-upper of "TLC Needed" houses. She explains DIY methods simply to homeowners who are not in the construction trades.

The underside of flooring coated with Borax "paint."

The underside of flooring coated with Borax "paint."

How to Kill Mold With Borax "Paint"

You might think someone can expect to find a little mold in any home, especially a home with a basement or which is located in a humid climate. However, there is such a thing as too much mold. And, where does that line between slight and intolerable lie? When you are challenged with the latter situation and cannot afford outside mold remediation services, one of the DIY options is to kill the mold with the detergent booster Borax (TM).

Step 1: Wear Protective Gear

Do not be casually confident that you are a healthy person and your immune system can defend itself. Be safe, not sorry. Buy a face mask and borrow or buy goggles.

  • Face mask: The face mask recommended for mold removal is called a respirator, which sounds more ominous than it really is. The P100 or N95 mask is what is required. These are made by several companies and have varying features. I love the 3-M N95 with a nostril valve. It allows for better exhalation and stays dry. Once I bought a cheaper N95 which had no nostril valve. It complied with the NIOSH standards, but the moisture in my exhaled breath condensed on the inside of the mask and I was feeling a damp mess on my chin.
  • Goggles: I normally wear glasses which have saved my eyes from injury many a time, as I do carpentry or gardening. However, my mold consultant strongly recommended eye goggles for anyone working above her own head. Naturally, painting a ceiling has one working overhead. So, I bought and used goggles which turned out to be very comfortable and not vision-obscuring.
  • Hair protection: My hair protection is merely an old ratty white T-shirt turned inside out as if I was pulling it off, but got stuck around my face. (Didn't you ever do this when you were a child?) I pulled the long ends in front of my neck and used a safety pin to attach them.
  • Clothing: Completing the gear are an old long-sleeved shirt and long pants and plastic clogs (socks, too.) I launder them separately from any other clothing.
Personal safety is paramount. When working on mold above your head, wear a respirator, goggles and a covering for your hair.

Personal safety is paramount. When working on mold above your head, wear a respirator, goggles and a covering for your hair.

Step 2: Prepare the Area

Identify the moldy area and brush or sweep away loose debris. Bag this and dispose of it. Then vacuum the same area, preferably with a HEPA vacuum cleaner. If you need to set up work lights, do this now. Also, gather any ladders or step stools you will need for the painting job. If you can open windows or doors to provide yourself with fresh air and ventilation.

Flooring with black mold after it has been brushed and HEPA-vacuumed.

Flooring with black mold after it has been brushed and HEPA-vacuumed.

Bring bright light to the work area.

Bring bright light to the work area.

Step 3: Make Borax Paint

Finding Borax in stores may be a bit of a project for you. It is considered a laundry product, so go to the clothes washing aisle of your stores. I have found it at a big box store (thank you, Supreme Being!), but usually there is only one box on a bottom shelf. If you find a large supply, I recommend that you purchase a box for every 300 square feet that you plan to treat.

Why Borax? It is not toxic to you, the homeowner, and it is effective in killing mold. All the safety equipment described above is for protection from the mold, not from the cleaning agent.

The recipe given is one cup of Borax dissolved in one gallon of water. HOWEVER - I found two problems with that. The first is that it is cumbersome for me to haul a 1-gallon container of Borax paint up a ladder to paint the underside of wooden sub-flooring. The more important reason for changing this, though, is because Borax is not the easiest material to dissolve. Or, to stay dissolved.

Therefore, I use 1/2 cup to 2 quarts of water—boiling water, that is.


  • 1/2 cup Borax
  • 2 quarts boiling water


I put the dry powdered Borax in a manageable sized 2+ quart saucepan (another advantage is the handle, which makes it easy to carry around), and then pour in boiling water from a teakettle and stir. This at least starts the paint as fully dissolved.

Some Borax will eventually settle to the bottom of the saucepan before I am done painting, but it is nothing compared to what sits at the bottom when I have used cold tap water. Since I work in either unheated or barely heated areas, the paint cools quickly and I am not in danger of burning my skin with scalding water.

Boiling water for the Borax mixture

Boiling water for the Borax mixture

Preparing Borax mixture

Preparing Borax mixture

Step 4: Paint Ceiling and Joists With Borax

Cover every bit you can reach with your "paint." It looks rather clear, more like cloudy water than an opaque white. When it dries, it will look much more white.

Cover every bit you can reach with your "paint."

Cover every bit you can reach with your "paint."

It will look rather clear, more like cloudy water than an opaque white.

It will look rather clear, more like cloudy water than an opaque white.

When it dries, it will look much more white.

When it dries, it will look much more white.

Good Luck!

I hope this helps those beleaguered with weather- and disaster-related wetness. You are facing a challenge and I hope it goes well for you.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: Can you paint over the borax concoction after it dries?

Answer: Yes, you can. First paint a lime chemical whitewash, then paint your desired color. The lime seals in any mold hyphae (roots) and prevents it from regrowing.

Question: Do you need to clean the mold off first and then paint the borax on or can you just paint the borax on and that then takes care of the mold? Will painting the borax on wood keep mold from growing again? This is in a crawlspace under a house on joists.

Answer: First, you absolutely must clean off the mold safely with a HEPA vacuum cleaner. Next, do the Borax paint and THEN: to seal the roots so that it does not grow back, do the whitewash paint. Be safe.

Question: I have a large area, about 1500 sf of subfloor I need to treat. Can I first spray a vinegar solution to help with the odor, then once it dries use the borax paint on this wooden subfloor?

Answer: Yes. Make sure the vinegar dries before going to the next step.

Question: Can I use borax for mold in a garage door?

Answer: Yes, as long as you are not impeding moving parts.

Question: I don't plan on painting after treatment with Borax (plywood roofing in attic). What would I follow up with to clean the mold off of the wood? My husband tried something from a big box store which he sprayed on and scrubbed. It did take some of the mold stain off, but I don't want to use anything so toxic.

Answer: In the mold treatment I describe, mold hyphae (roots) remain in the wood. The whitewash painting step seals them in, so they cannot do any more growing and "spewing." If you don't want to paint the wood, you have done only part of the process.

Question: I have unfinished pine planks as my interior flooring. The mold has been cleaned and removed from my subfloor, but I'd like to take precautions indoors. Would borax be a good method of treating my floors? Can the borax paint be cleaned off after a time?

Answer: If those planks are moldy, the hyphae (roots) of the mold organisms are probably deep inside and waiting. I would not expect to have them bare, raw, and natural again for a safe living space. I am sorry that this happened to your home.

Question: I am using borax on wood in an RV. Would you treat it more than once or have it tested before recovering? What about sanding any of the moldy spots?

Answer: Testing would be an excellent step! I do not see any value to sanding. The mold hyphae (roots) are deep in the wood. If you can replace the wood entirely and paint it before you cover it, that would be very good.

© 2012 Maren Elizabeth Morgan


Maren Elizabeth Morgan (author) from Pennsylvania on June 30, 2020:

JennyBlythe, I used dolomitic lime because that is that I could find in the big box store near me. It worked very well.

Good luck to you -- please consider getting and using a dehumidifier for the rest of your days to reduce the moisture/humidity that molds love.

JennyBlythe on June 29, 2020:

Hello, does it matter if you use pure quicklime or dolomitic quicklime for last part if project?

Maren Elizabeth Morgan (author) from Pennsylvania on November 12, 2019:

Jill, I am guessing that the cabinet is wooden. To be extra careful, I suggest that you do all the steps (vacuum, Borax, lime wash) to the entire cabinet - while wearing a face mask, of course. :-) Enjoy your project!

Jill Spencer from United States on November 10, 2019:

I'm really glad to have found your article, Maren. My project for next weekend is to chalk paint a cabinet with a little mold on the inside of one of the doors. I was wondering what to do about it. So I should paint with the Borax-water concoction and then give it a lime wash before painting?

Maren Elizabeth Morgan (author) from Pennsylvania on July 11, 2019:

Someone asked if Borax would work against termites, especially in combination with other chemicals. Since I ahve no expertise in termites and also no idea what will happen mixing Borax with fizzing household products, I decline to give an opinion.

Maren Elizabeth Morgan (author) from Pennsylvania on April 02, 2019:

Yes. You will allow it to totally dry and then paint your whitewash over it.

dave p. on March 28, 2019:

Once it is paint on you just leave it there?

Susan E. White on June 11, 2017:

I really appreciate you posting this for we poor people not just this mold cure, but also all the wonderful fantabulous tabs for home improvement & the like. Thanks a million. I used to work & probably could've almost afforded a professional, but now, I gotta do it myself. I was thinking about what you said about dissolving the Borax being a bit of a bear & I totally agree. Maybe you could use very hot tap water & put the Borax in the blender to break it down better, then add it to the full gallon (or 2 quarts) whatever works, but I hope you don't have to do this tiresome job again if you don't have to. I personally am going to put the solution in a larger garden pump-type sprayer, so I can really load up alot of Borax solution gallons & not have to change water alot. Mine has a shoulder strap which helps a little.

Maren Elizabeth Morgan (author) from Pennsylvania on February 08, 2016:

Jon, great idea.

Jon on February 08, 2016:

When I mix Borax with Murphy Oil Soap it dissolves very quickly. The ph of MOS is around 11 and Borax is above 9. It would be easier if I could take a bowl, brush, box of Borax and bottle of MOS down in the crawl space and mix as I go.

Maren Elizabeth Morgan (author) from Pennsylvania on December 23, 2012:

AliciaC, you are most welcome. Since you are a scientist - it is nice to know that you find this information vaild.

Linda Crampton from British Columbia, Canada on December 20, 2012:

Thanks for the useful information about borax, Maren Morgan, and thank you for describing the safety precautions that should be taken when trying to remove mold. I appreciate the details about respirators, too.

RTalloni on December 20, 2012:

Interesting information to have on hand in case of need. Thanks for easy-to-follow directions.