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How to remove and prevent black mold?

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Bruce Cowin

My sailboat is 9 years old, stored in a slip during the sailing season, and under a tarp during the winter months. I thought I had waxed and pollished everything well last spring. I noticed a problem last season after not using the boat for a few weeks. There were little black spots, specs, and splatters around the cockpit, lazerett, and on the inside hatch cover. I suspected I had black mold growing on or in the gelcoat. When I cleaned it with soap and water some of the spots faded but other spots remained. I've been using a solution of bleach and water, and scrubbing it with a brush on textured areas and a sponge on the smooth areas. This seems to only work temporarily, and I think I'm probably scrubbing some of the gelcoat off. I would like to find out if there is something I can put on the surface that prevents it from returning? Your suggestions will be grealy appreciated. Thanks, Bruce Cowin


Once you get it out...

Bruce, Mold is a persistant problem. They form spores and when you think you have it licked, their back. I would use a good mildew killer.After you have it licked, seal every thing you cleaned with Island Girl produces.This is something to talk to Jim Willis about. This is also on of his claims. I think he has an 800 number in Hawai. Blech is good but I think a mildewcide (sp)is better. It's a place to start... r.w.landau

Mary Connaughton


Bruce, I fought this problem for years on my boat. I'd clean the mold with bleach/water and then in a couple/three weeks it was back again. It was especially a problem after sitting during the winter months. This past summer I installed a solar/battery vent. It has a little fan that goes constantly. This seemed to do the trick. I'm happy to report that when I check on my boat yesterday, it looked as clean as it did when I left it back in November. It even smells good. What a relief! Cleaning mold is no fun. In fact it almost made we want to sell the boat.



I had two identical areas in my cabin, one on the port side one on the starboard, that were particularly bad for mildew/mold. I used to make it out to the boat every couple of weeks. When they'd get totally black (covered with mildew) I’d scrub them down with bleach. A couple weeks later they'd be starting to look nasty and in a month they'd be totally black again. Then I read somewhere to try white vinegar, so I thought I'd try a little experiment. I scrubbed one side down with bleach and the other with straight white vinegar. The vinegar seemed to last about 3 times longer than the bleach. In about a month and a half you could start to see some mildew on the vinegar side and it took 2 1/2 to 3 months for to get totally black and nasty again. So, until I find something better, I use white vinegar.
Sep 24, 1999
Hunter H46LE Sausalito
Scrubbing Bubbles Mildew Stain Remover

Works as well as X-16 and smells a whole lot better. Be careful with it though, it contains bleach. Put on the old jeans before you start spraying.


Jomax, ventilation, DampRid, A.C.

From what I understand bleach just changes the appearance of the mold but does not actually kill the spores. I use a mildewcide called Jomax (sold at hardware stores and home centers)in combination with bleach on my house and it seems to give me better results than bleach alone. Mold is a constant problem on the gulf coast since lead was banned from paint. Mold will return, the spores being blown from trees etc., but I see longer intervals between treatment using a midewcide. Try this in combination with ventilation and maybe some cans of DampRid. Someone told me their harbor charged a flat fee for electricity and they cut a hole and put a small air conditioner in the middle companionway hatch cover, letting it drain out of the cockpit. They let it run all the time and claimed it completely eliminated mold and the boat was nice and cool when they arrived rather than an inferno.

mike Johns

Grape Seed Extract!

I own rental homes and the big fear is someone will take you to court over mold. We have a company that uses grape seed xtract. This is a none toxic FDA aproved treatment.


Not Island Girl!!!

By now I'm beginning to feel like I'm on a crusade against Island Girl Products, and that's not at all the case. The Pink stuff is great on older boats - it's like a miracle. The rest of it is worse than useless. Useless would imply that it does nothing - good or bad. Worse than useless means that it does some very bad things if you're away from your boat for any length of time - and I'm talking weeks, not months. The stuff attracts pollutants, dirt, something - I don't know what it is, but I do know that it turns black and that it takes some serious scrubbing with Soft Scrub to remove it. Several of us on the dock used the stuff, were amazed at how great the boats looked. A couple months later, we were all at work with the Soft Scrub. Use it on a test spot before applying it to the whole boat - save your back for more useful things like lugging a six-pack to the boat.

Jim Bessinger

Black Spots

I find them easily removed with a strong mixture of clorox, about one cup to a half bucket of water and soap. Apply over a ten square foot area first, go back a scrub lightly, rinse and tey are gone. They come back about every two years in some small areas, which are easy to take care of when they are small areas. Maybee in Colorado mold isn't a big issue.
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