I spent several hours this weekend using 3M fiberglass restorer and wax rubbing out little black spots on my fiberglass deck. Two hours of work and only a very small area cleaned up. Does anyone know what causes these spots? Could they be mildew? They are not easy to get off, at least using rubbing compound and wax. It takes a fair amount of rubbing. Thanks, Greg W. "SlipAway"
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Could be mildew, could be spider dung
I use toget those black spots, too. Try washing your deck with bleach/water (1 cupa bleach to 1 gal of water). This should not adversely affect any wax/polish you have on the deck. Hope this helps!
I use toget those black spots, too. Try washing your deck with bleach/water (1 cupa bleach to 1 gal of water). This should not adversely affect any wax/polish you have on the deck. Hope this helps!
Soft Scrub
That's the advice I got on this board a couple of weeks ago. Worked brilliantly. Just Soft Scrub and a wet sponge. Very little rubbing. Mac
That's the advice I got on this board a couple of weeks ago. Worked brilliantly. Just Soft Scrub and a wet sponge. Very little rubbing. Mac
Black algae
If you have a lot of due or damp weather and it is an older boat, moister becomes a breeding ground for black algae, which is tough to get off. Take Ricks advice and use some bleach in the wash water
If you have a lot of due or damp weather and it is an older boat, moister becomes a breeding ground for black algae, which is tough to get off. Take Ricks advice and use some bleach in the wash water
Non-skid cleaner.
Greg: Non-skid deck cleaner works good on this stuff. Oxalic acid is what makes the non-skid cleaner work. If you can get ahold of this stuff it will clean it right up. Sometimes a tooth pick can be used to open up the algae and then these other products will remove it. The trick is to get the decks wet and let the cleaner to loosen it up. I have also used Island Girl Pink which also works. Personally I don't use softscrub. I think it makes the condition worse because it just opens the pores in the gelcoat. If you have a really bad case it may be your only resolution. Try all of the mentioned solutions until you find what works for you. Bleach and boat soap have not touched any of the black spots for us.
Greg: Non-skid deck cleaner works good on this stuff. Oxalic acid is what makes the non-skid cleaner work. If you can get ahold of this stuff it will clean it right up. Sometimes a tooth pick can be used to open up the algae and then these other products will remove it. The trick is to get the decks wet and let the cleaner to loosen it up. I have also used Island Girl Pink which also works. Personally I don't use softscrub. I think it makes the condition worse because it just opens the pores in the gelcoat. If you have a really bad case it may be your only resolution. Try all of the mentioned solutions until you find what works for you. Bleach and boat soap have not touched any of the black spots for us.
Spider poop
use Tidy Bowl cleaner from the Dollar store. It costs only guess what - a dollar. Mix it concentrated with a gallon or two of water, brush it on, let it sit for a while or overnight and hose it off.
use Tidy Bowl cleaner from the Dollar store. It costs only guess what - a dollar. Mix it concentrated with a gallon or two of water, brush it on, let it sit for a while or overnight and hose it off.
I Feel Your Pain
Greg, I spent last Saturday doing the same thing in 95 F and high humidity finishing the job I started 3 weeks ago. Small black specs like pepper all over the deck. My dock neighbors say it is soot from either the power plant or the steel mill that are within a few miles of our marina, but I have my doubts. 3M rubbing coumpound worked best on smooth surfaces, but not very effective on the textured fiberglass surface on the foredeck or the cockpit. I used a stiff bristled scub brush and a spray bottle of a mildew removing bathroom cleaner with bleach in it. That worked pretty well but it was slow going. The grey non-skid on the side deck cleaned up pretty well with a soft bristle deck brush. I don't think there is an easy solution. Bob R S/V Unfurled 2002 H356
Greg, I spent last Saturday doing the same thing in 95 F and high humidity finishing the job I started 3 weeks ago. Small black specs like pepper all over the deck. My dock neighbors say it is soot from either the power plant or the steel mill that are within a few miles of our marina, but I have my doubts. 3M rubbing coumpound worked best on smooth surfaces, but not very effective on the textured fiberglass surface on the foredeck or the cockpit. I used a stiff bristled scub brush and a spray bottle of a mildew removing bathroom cleaner with bleach in it. That worked pretty well but it was slow going. The grey non-skid on the side deck cleaned up pretty well with a soft bristle deck brush. I don't think there is an easy solution. Bob R S/V Unfurled 2002 H356
My pain
Based on the difficulty I was having removing, I figured the only way would be by much effort! The worst of it is in the center of the diamonds within the nonskid. Probably because it holds a bit of moisture longer. I just hope once I clean up, it remains clean. Greg W "SlipAway"
Based on the difficulty I was having removing, I figured the only way would be by much effort! The worst of it is in the center of the diamonds within the nonskid. Probably because it holds a bit of moisture longer. I just hope once I clean up, it remains clean. Greg W "SlipAway"
Artillery Mold Spores
Your area may have something called artillery mold spores. This is a mold that spreads its spores by "exploding" and showering all nearby surfaces with small (< pin head size) black dots that stick like they are welded. I occasionally get them on the sides of my hull over the winter. I can usually get them off with hard rubbing with a mild solvent or with a paste wax or somethimes with my finger nail. The longer they are on the surface, the harder they stick. It is easy to damage the gel coat being too aggessive with these things.
Your area may have something called artillery mold spores. This is a mold that spreads its spores by "exploding" and showering all nearby surfaces with small (< pin head size) black dots that stick like they are welded. I occasionally get them on the sides of my hull over the winter. I can usually get them off with hard rubbing with a mild solvent or with a paste wax or somethimes with my finger nail. The longer they are on the surface, the harder they stick. It is easy to damage the gel coat being too aggessive with these things.
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