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stained gelcoat


Today i went to wax and wash the hull of my catalina 27 and found a bad stain on the bow i couldent remove. Long story short somehow the yard (who i paid to do the wok) didnt winterize the marine head properly and over the winter it overflowed out the vent into my anchor locker which drained overboard causing a long dark blue stain on the outside of the hull from the tolit chemichals which were in the tank. I tried everything i had including hull & deak cleaner and acetone but wasent able to do anything. If anyone knows of a cleaner or chemichal that would work on a stain like this i would love to know about it.-----(moral of the story, dont trust anyone else to do work on your boat)

Thanks for any help


Try oxalic acid, I tried it on a Hobie 14 hull many years ago and it got rid of stains
and cleaned up white hull real good, I think drug stores have it maybe Walmart.


I looked in a walmart/drugstore and couldn't find oxalic acid. Where can I find it or what section of a store would it be in?


In drug stores there's an apothecary shelf where you find some raw chemicals like boric acid and potassium nitrate. Sometimes there. In the hardware store they label it wood bleach. In the grocery store it's a component of Bar Keeper's Friend cleanser right near the comet and ajax.

Have you called the toilet-chem company and asked what works on their dye? :rolleyes:

Alan Glos

Active Member
Another good stain remover is called FSR (Fiberglass Stain Remover) available at any good motorboat products store but it is pricey and I think the active ingredient is the aforementioned oxalic acid. Also try straight laundry bleach.

Alan Glos
Cazenovia, NY

zigga zagga

New Member
:)The product I use is Mary Kate stain remover. Available most marine stores in a liquid and also gell form. Works similar to FSR but is mre agressive in its cleaning ability and will not harm the gelcoat.

aka Zigga Zagga


The end result would likely be more against the moral of your story, but I would think this would be the problem of the yard that winterized and stored your boat... at least up to the purchase price of the service they failed to provide...


acetone but wasent able to do anything. I bet it stained the gel coat yellow. Never use it on gel coat unless you know what your doing.