Q: I’ve heard MEK or acetone is great for removing marks in gel coat. Is it OK to use or will it ruin the gel coat in any way?
A: I would save strong chemicals such as MEK or acetone as a last resort gel coat stain remover. First try a multi-purpose, biodegradable cleaner such as Pure Oceans All-Purpose Spray or even Simple Green in its more concentrated form. If the mark or stain isn’t coming off with a spray cleaner, then try a cleaner wax or rubbing compound. Just squeeze a small drop of it on a cloth and try rubbing the stain away. Remember that there is no wax in rubbing compound, so if you use it to remove a stain, you’ve also just removed any wax that was in that area, so you’ll want to apply another layer of wax for continuous protection.
If those things aren’t working and you want to try a stronger chemical such as acetone or lacquer thinner, then just pour a small amount of it on a rag and wipe it over the stain. These types of products will probably remove the stain, but consider that they’ll also remove any wax in that area, just as the rubbing compound will. This won’t hurt the gel coat in any way, but if you use strong products like this on gel coat, always follow up with another coat of wax in that section.