How to remove yellowing gelcoat on the non-slips?

[Clevermoray]

Dear Sailors,
I have a yellow gelcoat problem on the non-slips on the different catamarans , some plates have yellow spots on the edges, some all over.

I bought my catamaran a year ago and I am looking for a solution to this problem please advise…

Please see attached pictures

Best ,
Clevermoray.

[smj]

If looking at that correctly, I would be more worried about the possible stress cracks than the discolored gelcoat. What kind of cat?

[Clevermoray]

Thank you for your answer, there are no stress cracks, I just have a yellowing problem on the non-slip plates. This is the cruising cat.

[smj]

Ok, looked like stress cracks below your phifertex covers over your windows

[sailingharry]

I have had excellent results with yellowing in gel coat, both the brown stain on the bow, and yellowing of white deck surfaces.

I use a 25% mixture of OsPho. I mix it in a garden sprayer, and just spray it on and let it set. Some stuff can take 10 or 15 minutes to fade. It is equally effective on rust stains from the anchor chain, and rusty spots that form on stainless.

You can get it on Amazon, but if money is no object, West Marine will overcharge you for it and call it Marine Descaling Fluid. Same stuff, phosphoric acid.

[Uncle Bob]

To my eye it appears that the boat has at some stage been painted and what you are seeing is deteriorating painted finnish.

[Matt Johnson]

I think it's been resprayed in that area. It looks like the discoloration from an additive or thinner for the gelcoat repair.

[heavyworks]

Originally Posted by sailingharry

I have had excellent results with yellowing in gel coat, both the brown stain on the bow, and yellowing of white deck surfaces.

I use a 25% mixture of OsPho. I mix it in a garden sprayer, and just spray it on and let it set. Some stuff can take 10 or 15 minutes to fade. It is equally effective on rust stains from the anchor chain, and rusty spots that form on stainless.

You can get it on Amazon, but if money is no object, West Marine will overcharge you for it and call it Marine Descaling Fluid. Same stuff, phosphoric acid.

Which Ospho product do you use? And do you just mix it with three parts water? On Amazon it says it is only good for rust.

And don’t you need to use some sort of sealant afterwards? I guess it would not last long at all if you don’t cover it with the right kind of protective coating.

[sailingharry]

Originally Posted by heavyworks

Which Ospho product do you use? And do you just mix it with three parts water? On Amazon it says it is only good for rust.

And don’t you need to use some sort of sealant afterwards? I guess it would not last long at all if you don’t cover it with the right kind of protective coating.

Frankly, I didn't know there was more than one product by OsPho! It's a blue liquid, comes in quarts and gallons. It doesn't need a sealant afterward, it eliminates the stain. The stain typically has an iron content, which is probably why the acid does the trick. For a cheap and simple test, you can steal the brown bottle of "Wink" from the admiral's laundry closet. I think that's hydrofluoric acid, but it does the trick just as well. On the hull, I do follow it up with two (or three!) coats of Collonite, but I'm the deck I don't do anything. West also carries various paste products that do the same thing, but they are more expensive.

Just remember the old adage my father taught me:
"In chemistry, do as you outta, add the acid to the watta."
Or if you're more interested in excitement:
"In chemistry, don't be placid, add the water to the acid."

[Flatswing]

Or you can use Davis FSR (Fiberglas Stain Remover) or Y10, both are gels that you brush on and rinse with a hose after 2 minutes. Starbright also makes a spray-on product. I tried it today and it works equally well on stains and rust stains, but the sprayer bottle it came in was rubbish. Barkeepers friend cleanser is a powder with similar ingredients. More difficult to use on vertical surfaces such as hull sides. BTW, here in SC, Ospho is green, not blue. I wouldn’t use it for rust stains ‘cus it converts the Iron oxide into a stable (but black) compound. Great for rusting steel tools, but not the best for removing rust & other stains imo.

[sailingharry]

Originally Posted by Flatswing

Or you can use Davis FSR (Fiberglas Stain Remover) or Y10, both are gels that you brush on and rinse with a hose after 2 minutes. Starbright also makes a spray-on product. I tried it today and it works equally well on stains and rust stains, but the sprayer bottle it came in was rubbish. Barkeepers friend cleanser is a powder with similar ingredients. More difficult to use on vertical surfaces such as hull sides. BTW, here in SC, Ospho is green, not blue. I wouldn’t use it for rust stains ‘cus it converts the Iron oxide into a stable (but black) compound. Great for rusting steel tools, but not the best for removing rust & other stains imo.

a $25 gallon of OsPho will do my 43' hull several times over. How does that compare to the cost-effectiveness of Davis or Y10? I can spray it on with a garden sprayer and get the entire hull in 10 minutes, I can even reach it while the boat is in the slip -- substantially easier than a cream I think. I'm pretty sure they are all acids and work similarly.

I won't argue green versus blue. Both sort of seem to be the correct name.

I have had no troubles with it leaving black stain behind, even when used on rust stains.

[Flatswing]

Originally Posted by sailingharry

a $25 gallon of OsPho will do my 43' hull several times over. How does that compare to the cost-effectiveness of Davis or Y10? I can spray it on with a garden sprayer and get the entire hull in 10 minutes, I can even reach it while the boat is in the slip -- substantially easier than a cream I think. I'm pretty sure they are all acids and work similarly.

I won't argue green versus blue. Both sort of seem to be the correct name.

I have had no troubles with it leaving black stain behind, even when used on rust stains.

That’s very informative, thanks for that.
I use Ospho frequently on rusting tools and fittings ‘cus it turns rust into iron phosphate, which is a stable compound that can be left or painted without priming but it appears black to me. I’ll give it a go on the hull sometime. (Btw, never considered doing the entire hull at once, typically a jar of FSR lasts me a couple of years or more. I’ve used the same 3” chip brush for the past 7 yrs. So no sprayer required.)