by Roger » Wed Sep 12, 2007 11:10 pm
I would start with any household cleaners you think may work, like mr clean magic eraser, tilex, etc. For fg work try to stay away from the abrasives like comet, or chemical cleaners that will soften the gelcoat like acetone.
When (and where) those fail, move on to the heavier duty (and more hazardous) cleaners like oxylic acid, mild muratic acid, and the like. Make sure you understand the hazards and protect yourself accordingly.