Fiberglass Stain Removers

Alan Glos

Alan Glos

Active Member
I am currently working on a mid-1980's white Sunfish hull that was moored in a lake all summer. The bottom has some stubborn stains that are probably a combination of organic material (algae) and a little surface oil from motor craft. I tried a little household laundry bleach and the bleach does not remove this staining at all.

Several years ago I was working on a similar project and bought a bottle of Fiberglass Stain Remover (dubbed FSR) and it worked great. I don't recall the brand but it was a low viscosity liquid that was very effective.

Do any of the Forum readers have experiene in this area and if so, can you recommend a particular brand of stain remover? Fire away.

Alan Glos
Cazenovia, NY
 
Many freshwater marina's use a diluted muratic acid solution to clean the bottom of boats. They spray it on with a garden sprayer, brush it, let it sit a while and then rinse it off. Check with a local marina.
 
It’s mostly elbow grease. Here are a few thoughts in a stepped approach –

Slime, crud, and heavy oxidation from months or even years in the sun –
Kitchen Cleanser, just not soft scrub types – you want the abrasive action, and lots of elbow grease, 2 or 3 go-arounds may be needed. Scrub like you are sanding – because you are to a small degree.

Rust and organic stains –
Oxalic Acid (Bar Keepers Friend or Wood Bleach) Don’t apply acids or bases full strength, follow the dilution directions for the wood bleach.

Stubborn stains, spot cleaning –
Dow Scrubbing Bubbles (aerosol seems to work better over the pump bottle formula)
The first two cleaning methods must be used before trying this one to remove all the heavy crud. Start with a dry hull, let the Scrubby Bubbles sit 20 – 30 min without drying out.

Also – dilute chlorine bleach or very diluted muratic acid (check dilution level for fiberglass swimming pools) DO NOT MIX these two. If you do use both separately, rinse extremely well inbetween. Both will attack all the metal parts especially a Base like the bleach attacking the aluminum so be very careful there.

Last resort – sand down the stained gelcoat -
600 to 1000 grit wet sand.

Bring back the shine –
Rub out with rubbing compound. Power buff if you have it or rub like heck.

Preserve and protect –
Quality boat wax and-or gelcoat cleaner-preserver systems.
 
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