Borax: Formula B, Stopping Mildew Cheaply and Effectivly, and How the EPA Can Make Everything Complicated

rev. 4-20-2014, rev. 4-9-2024

This 10-year old blog post describes some work I did on mildew prevention 10 years ago. I took it down because I published a few articles on the topic, but here it is again. I'll post a follow-up in a few weeks with some other stuff I've learned.

Websters' version

Borax: 1. a white crystalline compound that consists of a hydrated sodium borate Na2B4O7·10H2O, that occurs as a mineral or is prepared from other minerals, and that is used especially as a flux, cleansing agent, and water softener, as a preservative, and as a fireproofing agent.


EPA's Version

Borax: pesticide products containing boric acid and its sodium salts (borax) are registered in the U.S. for use as insecticides, fungicides and herbicides. As insecticides, some act as stomach poisons in ants, cockroaches, silverfish and termites, while others abrade the exoskeletons of insects. As herbicides, some cause desiccation or interrupt photosynthesis in plants, while others suppress algae in swimming pools and sewage systems. As fungicides, several are wood preservatives which control decay-producing fungi in lumber and timber products.

http://www.epa.gov/oppsrrd1/REDs/factsheets/0024fact.pdf

While generally considered safe--still used in many big-name laundry detergents--if I claim a cleaning formulation containing borax keeps mildew away, I have to register it with the EPA before marketing. But I can sell you a box of borax without registration. Go figure. Is it really about safety? I don't think so. Borax is only about twice as toxic as washing soda (LD50 borax and boric acid are about 2500 mg/kg BM. Although borax is suspected in certain reproductive problems in laboratory animal testing, it is not associated with cancer and does not bio-accumulate.).

It seems that anything that works must be poison, or at least regulated. That is governments purpose.

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As part of a future Practical Sailor article I began exploring fumigating agents and anti-mildew products. I truth, most projects I take on are because I've had some troubles related to the subject in question and thus have some understanding and some additional motivation. Every boat has at least one damp spot prone to mildew, and in my case, I have a basement prone to wet carpets every few years. Not flooding, but mildew potential.

I began exploring the formulations of some successful products. Concrobium is one, dreadfully over priced at the local hardware, particularly considering you can look up the underlying patents (EP 1104450 B1) and learn that each quart bottle ($18.00) contains nothing but:

• 1 tbs baking soda (sodium bicarbonate)
• 2 tbs washing soda (sodium carbonate)
• 2 tbs TSP (trisodium phosphate)

Simple and effective. The chemistry makes perfect sense; it is applied without rinsing and thus leaves behind a thin alkiline coating that repells bacterial and fungal growth (fungi require acid conditions) and provides no food for growth (soaps contain fatty acids and make great fungi food). More is not better because it is used without rinsing, the limitied concentration is important.

That got me thinking, so I began trying other variations including my favorite, also in 1 quart:

• 2 tbs baking soda
• 2 tbs borax
• 1 tbs TSP

I've been testing all three on some mildewed carpet sections, cleaning by scrubbing lightly and then extracting with a vacuum. Which is best? After 6 months they are both perfect, although the borax version killed the smell a bit faster.

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Other Applications

Basement Carpets and Walls. We've had problems with a wet basement and biannual flooding for 20 years. I've washed and dried a lot of carpets. Learning to use this formulation as the rinse was a revelation. No more mildew smell, no more mad rush to get them dry. No more black stains. Simply use this as the rinse water and the carpets stay fresh.


Preventing Wood Rot

Borax is VERY effective in preventing wood rot. I've used it myself mixed with ethylene glycol (Goolge it) to preserve a common pine totem pole in damp soil and remain impressed; it's staying as though it were pressure treated, 6 years and counting. West Systems Epoxy has posted on this subject. The National Park Service posted this on preserving totem poles in the PNW with borate/glycol.

Bugs

Obviously, they can't stand boric acid. One of the most common extermination products, particularly around kitchens and bedrooms (works on mattresses). It's not going to work on the flying pests, though, the only ones I have trouble with. Darn.

Wooden Decks

Seems like a good cleaning choice. Should help keep the algae away. Limit the TSP if you wish to be bay-friendly. Try it on your home deck for a little boost to the pressure treatment.

Combine it with some bleach as needed.

Sails

A less alkaline variation is well known and should keep the mildew away. Reduce the dose:

• 1 tsp baking soda
• 1 tsp borax

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Oh, the power of good marketing. I swear I'm not just trying to be trying to be cheap. Furthermore, I'm a chemical engineer and have no phobia regarding synthetic chemicals. I'm not pushing this because of some hidden green agenda or because it is less toxic. The strength of these formulations is basic:

• No organic mildew food
• Mildly alkaline film
• Borate as mildewstat

I'm also reviewing some nice complex organic formulations that promise better water resistance. We'll see.