This guest post is from Drew Frye and first appeared on his blog, Sail Delmarva. Drew also tests products for Practical Sailor magazine and writes for others like Good Old Boat magazine. He graciously agreed to let me reproduce his article here.
The great myth of boat ownership—other than believing that everything takes 3 times as long and costs 4 times as much as you expect—is that mildew is ubiquitous. No matter how leak-tight, no matter how well maintained, it is always there. Well, I disagree wholeheartedly, and I challenge anyone to find any in my cabin. How have I dodged this scourge?
First, do keep the boat leak-tight. That means no water in the bilge and no leaks around deck hardware. Not that hard if you mount things right. Strong enough so they don’t move, bedded with polyurethane caulk or butyl rubber.
Second, if there is a leak that starts some growth, treat it right. In fact, I’ve learned far more at home, cleaning a basement that has fallen victim to occasional flooding, than around boats. The key is a cleaner with the following characteristics:
- Controlled alkaline pH. Mold and mildew prefer slightly acidic conditions. While vinegar has a faithful following, I was able to demonstrate in head-to-head testing that in damp conditions alkaline treatments are more effective.
- No food. Again, vinegar is a problem because it becomes mildew food when the dampness returns and can actually accelerate growth. Likewise, soaps and detergents are a problem; the mildew uses them as food.
- Can be left in place and NOT rinsed off. Or rather, the rinse must contain the inhibitor. For this reason, do NOT increase the dosage in the hope that more is better, it isn’t.
- Contains an additional agent that is toxic to mildew. In the second formula that I recommend below, borax is a powerful anti-mold agent and anti-bacterial.
- Not bleach. While bleach can be effective on the surface, it is damaging to many surfaces and then when it dries, the pH is far too high.
You could troop down to your local home improvement store and pay many dollars per gallon for pennies worth of chemical in a bottle. Plastic, shipping, markup, and paying for know-how all cost. Or you could simply brew up something at home that has proven to be more effective.
Unlike bleach, both of these formulas require some scrubbing. Some pre-soak time helps to kill the organisms and loosen the bonds. After that, add a little elbow grease. If you need to rinse, remember to re-treat to provide protection from re-infection.
Concrobium is a top performer in many independent tests. It is also dead simple, easily formulated from stuff you can get at stores you already go to.
DIY Concrobium knock-off formula:
- 1 quart hot water
- 1 tablespoon baking soda (sodium bicarbonate)
- 2 tablespoons washing soda (sodium carbonate)
- 2 tablespoons TSP (trisodium phosphate)
This works better than all the commercial formulas on natural fibers and better than 90% of the commercial formulas on synthetics (there are a few specialty formulas based on silicone quaternary amines that are more effective on synthetics). But in head-to-head testing using canvas strips in special mildew chambers and on old PFDs I treated in strips and then left under a backyard shed, the clear winner was always a borax-based cleaner of my own formulation. Again, the key is to maintain the correct concentrations. Don’t add any detergent, which will only become mildew food and leave the final rinse of this treatment to dry in-place. For most cleaning, all that is required is to spray the area until wet, scrub vigorously, and wipe off the excess.
This formula has been a lifesaver on wet basement carpets. The last time we had a flood, I had injured my back and was unable to get the carpet cleaner out for several weeks. It had begun to reek of mildew. However, going over the carpet with this borax formula, once as a cleaner, and then a second time as a rinse, not only removed most of the mud and mildew, but also killed the smell and prevented all growth, even though the carpet stayed wet for a few more days. The stuff is a miracle.
Borax mildew treatment:
- 1 quart hot water
- 2 tablespoons baking soda (sodium bicarbonate)
- 2 tablespoons borax (sodium borate)
- 1 tablespoon TSP (trisodium phosphate)
[$tingy note: If you don’t understand why there’s a picture of a 20 mule team with this post, ask your parents.]
By the way, it is also very effective for cleaning mildewed drywall before painting. The mildew will be killed, it will not return, and the residue will not affect paint adhesion.
Why is this formula not sold in stores? One reason is that claiming it kills mildew would require registering it as a pesticide. So long as common chemicals like borax are sold as generic ingredients, they are exempt from regulation, but the moment you formulate and make claims, the status changes.
But the real answer is that I don’t know. I can only assume that the sellers of cleaning agents believe folks will buy a bleach based, quick cleaning product, but can’t understand the benefits of prevention. They may be right, but I think sailors can understand.
So this is my gift to you, the most effective anti-mildew cleaner available for pennies. Enjoy.
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