brown spots on hull

[brad minda]

I have three fiberglass boats all with white hulls from two different manufacturers. all are from the mid 80's. Two are in the Oakland CA estuary and one is on a trailer at my house in the central valley of California. All three have recently developed small brown spots that look like rust spots. I have tried pressure washing, goof off, soap and a rag and nothing seems to budge them I even tried a 25% mixture of bleach and nothing. The only thing I haven't tried is wet sanding the spots. Wish I had a picture to add. Any ideas.

 

[Stu Jackson]

FSR it's gelled oxylitic acid

I call those spots or stains mustaches.

Clean 'em up and then apply wax or they'll reappear.

 

[brad minda]

What do you recommend for cleaning them up

 

[Joe]

What do you recommend for cleaning them up

I think he recommended FSR as a cleaner. Or you can use an acid based toilet bowl cleaner. Check the label, you want acid... not bleach. Hydrochloric acid (HCL) is the most common in toilet bowl cleaner.

 

[Tom G P-21]

Cleaners with oxalic acid would be you first line of attack. Bar Keepers Friend is the most commercially available version. There are other powders with higher concentrations you can buy at hardware stores. For tough spots I put a little Bar Keepers friend directly on a damp sponge and a little elbow grease.

 

[rgranger]

Oxalic acid goes after rust and tannin stains very efficiently.

 

[JamesG161]

You can also use Naval Jelly (phosphoric acid) both Acid are available at you home center. Never mix with bleach and remember Acid handling safety.
Jim...

 

[Rick Webb]

Cut a orange in half and rub it on the spot.
Florida oranges taste better but California ones work fine too

 

[JamesG161]

Cut a orange in half and rub it on the spot.

Squeeze the oranges, make pitcher of Tequila Sunrise's, sip it while watching your helpers use the orange rinds to clean the boat.
Jim...

 

[Ron20324]

Try "On & Off". Most boat supply places have it. It's caustic, so don't breath the fumes. Last week I was on the hard, and a friend/skipper was helping me with the hull cleaning. She had never heard of O&O. She was amazed the brown mustache on the hull went away within a few second os application.

 

[rgranger]

Try "On & Off".

On & Off is a mixture of hydrochloric (muriatic) acid, phosphoric acid, oxalic acid and a surfactant. So it is a mixture of the suggestions given here.

BTW: Caustic means basic