Is this just dirt?

[Ctmangrum]

This started showing up on my boat recently. Comes off with some serious scrubbing. Whats the best way to get rid of it? Power wash? Chemical then scrub? Thanks.

[bud37]

Looks like a mildew......it gets into the porous gelcoat. Try a small area with some weak bleach and water solution in a spray bottle, rub with soft brush then rinse off with hose. You should see it fade and disappear..try a weak solution first in small areas till you get the hang of it......then seal it with a good cleaner wax. That is the way I used to do an old boat we had, it came up nice and white without sanding off gelcoat which is never good with an older boat.

It will return especially on the damp side of the boat if you don't stay ahead of it every now and again.

[Midnightsun]

A pressure wash will also get rid of it but as mentioned, a mild bleach solution will keep it at bay.

[Phrancus]

Pressure wash is not always as harmless in the long run as many think. I'd use that bleach solution - but carefull when you spray it: not only to where it lands where it will bleach but also for your lungs and eyes. A wet towel does the job too. Point is to give it time to bleach before it dries up. Rinse with clean water, mind that the runoff water can still bleach....

Filling the pores with a wax can help a bit but obviously pay special attention to the walking areas so you do something to have some grip there.....

[bud37]

I agree about the pressure wash........something I have never used on a boat. In the wrong hands they can damage gel, get under sealers and caulking, blow stuff everywhere ( slip neighbours ) and the noise !!.......my considered opinion.
We just used old cloths to catch the drips then when you wash with lots of water all is well........the bleach breaks down quite quickly after contact with organic matter and sunlight.

[Midnightsun]

Maybe I should have been more specific regarding the pressure wash. Do not use a 3000psi gas powered unit as this is way too strong. Personally I have one on board, pretty small and pretty quiet which does a good job and obviously no more powerful than a 110v outlet will allow and in comparison to gas is rather weak. Do not hold the nozzle an inch from your work, stay at least 6 inches away for the really tough areas and farther for general cleaning. I have mistakenly run it over my bare foot once while cleaning, did not even break the skin or cause any pain however it did scare me. That being said it is used once or twice a year and 99% of this is on the nonskid surface which we all know is a bear to clean. This is what I carry. https://www.homedepot.ca/product/ryobi- ... 1001662889

Found this which is seems to be similar in performance and noise to the one I have however I think the Ryobi is a little smaller.

[Carpediem]

Starbright makes a non-skid cleaner polish that many sing the praises of. I have used it as well and find that it works well to remove the black stains and it helps keep them from returning if applied at each end of the season. It is also imperative to rinse the boat down every chance you have to keep the dust and mold spores off the surface. Most boats that wave these issues just don't get the regular care that is required so the issues are allowed to build until it is a real chore to deal with. It is just a part of boat ownership, the struggle of dividing the time of enjoying the boat with family and toiling to keep it looking as nice as possible. No one is immune!
Carpe Diem

[Ctmangrum]

The pressure washer I have is low pressure and nothing im worried about. Ill try a little bleach and look for that starbrite sealer. I have deck cleaner but no sealer. Thanks for all the advice.

[Midnightsun]

The Starbrite stuff does work well however what makes it work is simply the bleach they have in it, no magic going on there. Very effective and recommended product though.

[Ctmangrum]

You think its good as a preventive measure? Does it have something that will block it?