Homemade Mildew Preventers That Really Work

Posted by Darrell Nicholson at 04:13PM - Comments: (13)

Drew Frye
Drew Frye

Practical Sailor tested several mold preventatives on cotton-duck canvas.

If youíre getting ready for sailing this summer and feel like you are still losing the battle with mildew, then youíll definitely want to read our report in the November 2013 issue of Practical Sailor. PS tester Drew Frye made a pleasant little discovery when he was researching and testing various anti-mildew protectants. Two inexpensive homemade concoctions did as well as or better than retail formulas that are 20 to 100 times more expensive. It wasnít a huge a surprise for Frye, who based the homebrew formulas on some of the more effective anti-mildew products from our previous tests.

The 13-product test field comprised liquid sprays, and gels and solids that work through emitting a vapor. The three vapor products were Star briteís NosGUARD SG, which reacts with water to release chlorine-dioxide gas; Forespar Tea Tree Power, a tea tree oil-based gel in a vented tub; and Pur-A-Fy Air from Natureís Innovative Solutions, a lemongrass oil-based gel.

Drew Frye
Drew Frye

PS contributor Drew Frye at work in his floating "lab," a PDQ 32 catamaran.

The liquid-spray group included Foresparís Tea Tree Oil Spray, Henkle Chemicalís Renuzit, Siamons Concrobium, Goldshield, and 3Mís Marine Mildew Block, which did well in our June 2010 test. Concrobium is available in liquid and vapor form; we tested the liquid. Our most effective commercial product, Goldshield 5 (diluted to the equivalent of Goldshield 75), is an quaternary ammonium formula developed by scientists at Emory University. As our dehumidifier field tests demonstrated, the first line of defense is controlling humidity. Something I have touched on in previoius blog posts about fighting mildew. For sealed lockers, or tight quarters that are difficult to treat or ventilate, you might also want to look at our report on chemical dessicants like DampRid.

The two homemade spray formulas we tested each cost about one penny per ounce. Like the other mildew preventers in our test, you use these as cleaners by simply spraying the product on, wiping any excess away, and leaving it on. Before applying to any fabric, test the spray on an inconspicuous sample spot.

Formula A

1 quart hot water

1 tablespoon baking soda (sodium bicarbonate)

2 tablespoons washing soda (sodium carbonate)

2 tablespoons trisodium phosphate (TSP)

Much like Concrobium (which it is modeled after), our homemade Formula A removed the mildew from test carpet on board and kept it away, even though the area got wet again. It was also very effective in the moist-environment lab test.

Formula B

1 quart hot water

2 tablespoons baking soda

2 tablespoons Borax

1 tablespoon TSP

Formula B was the second-place performer in the liquid group. It was certainly the best value. It cleaned well, prevented mildew from returning to the carpet, and greatly slowed mildew infection in the moist-environment test in the lab.

We also tried treating with plain vinegar, which reportedly works on some hard surfaces, but testers found the smell a little too overpowering. A 10-percent solution of household bleach (3-percent sodium hypochlorite) was one of the best cleaners, but this has to be used with care. Bleach will bleed or degrade many fabrics, and can harm the marine environment. For complete results and more tips on keeping your boat mildew free, be sure to check out the full test report on mildew preventatives at www.practical-sailor.com. Non-subscribers, or those who'd rather save some time and support our testing program, can also dive into our complete two-volume report on mildew cleaning and prevention The Mildew-Free Boat, which will help you take care of mildew once and for all, with minimal effort.

For serious cleaning jobs ahead, we also have an e-book dedicated to Marine Cleaners, covering everything from waxes to teak cleaners to metal polishes.†

Comments (12)

Can you please confirm how well this DIY recipe works compared to the store bought Concrobium? I have mold in my new construction basement on the drywalls and do not want to spent 100's of dollars on Concrobium if I can make a similar solution myself.

Posted by: TDJack | July 30, 2019 7:39 AM    Report this comment

Thanks Drew! Is it better to mix up a batch for each use, or is it shelf stable?

Posted by: Damon | January 29, 2019 2:15 PM    Report this comment

If TSP is not available, increase the washing soda to 3 tablespoons. Because borax is the main active ingredient, it will still be an effective preventative.

Posted by: Drew Frye | June 30, 2018 9:53 AM    Report this comment

TSP is not sold in Wisconsin. There are phosphate-free substitutes, but I think they may be sodium carbonate. Is this a deal breaker on these formulas?

Posted by: Mark G | June 21, 2018 5:51 PM    Report this comment

In the photo you show Drew Frye using a bottle of Nikwax TX.Direct waterproofing spray to apply product, however this product is not mentioned anywhere as being one of the ones tested. Since I am familiar with the product in other applications, I recognize the label. It's ingredient list does not contain any of the formulas you have come up with here, so I'm guessing Drew just used the empty container. Please, if you're going to use the empty container of some other product, maybe don't use photo of it in the publication. It's just confusing and misleading. Or if you used that product, why is it not mentioned in the article?

Posted by: BC | May 13, 2018 10:53 AM    Report this comment

Washing soda-
most grocery stores in the detergent aisle, usually near borax, Arm and Hammer brand is most common.
Cautionary- bleach(sodium hypochlorite) or other concoctions introducing halides into the bilge can result in a serious and tenacious form of corrosion. Look up 'pit corrosion'.

Posted by: Mystic | May 10, 2018 3:52 PM    Report this comment

At the close of every season when my boat is on the hard I pour about 1-2" of DampRid (no scent) into about 20 plastic tubs (like those from cottage cheese, soft butter, etc) and place them all around my boat in the lowest spots I can access. In the spring I find most of them filled with water which I empty. I then rinse the containers and store them for next season. Boat smells great, never a sign of mildew.

Posted by: Silversailor | May 10, 2018 12:37 PM    Report this comment

Lemon oil on wood surfaces is VERY effective, not only in removing mildew but in keeping it from coming back.

Posted by: DavidM | May 10, 2018 12:07 PM    Report this comment

Washing soda can be found at most grocery stores, or a neighborhood hardware store. It's quite common. Not the same as baking soda.

Posted by: Roland52 | July 10, 2017 8:53 AM    Report this comment

We did not test Kanberra gel in this comparison, but it also uses tea-tree oil like the Forespar products. We did try some Kanberra gel previously in a test boat in Florida, and results were comparable to what we found in the more controlled comparative testing done in the Chesapeake for this article. Seemed to help control mildew and odors, but was not as effective as other spray-products we used.

Posted by: sailordn | October 18, 2013 10:10 AM    Report this comment

The item tested that you called: "tea tree oil-based gel in a vented tub". Is this the product called Kanberra Gel or is it the same chemical?

Posted by: Larry C | October 16, 2013 10:28 AM    Report this comment

Washing soda? Never heard of it, so, where would I find it?

Posted by: John T | October 15, 2013 9:51 AM    Report this comment

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