Gel-coat black stains

[Crime Pays]

We are looking at a 1989 FU HWA Taiwanese trawler. Can anyone tell what is going on with the gel-coat on the upper half of boat? Nothing below the rub-rail. Any suggestions on a fix? We are thinking vinyl wrap on the vertical areas, and DP or ALEXSEAL® Yacht Coatings on the flat areas. What do you think has happened to the gel-coat?

 

[FF]

Try a power wash first.

 

[Pete Meisinger]

I would try to power was first but don't expect a miracle. From the looks of it you have oxidation and the power wash might remove a sort of clear coat.

Wash it well, use a heavy primer like Brightside "precoat" then Brightside one part epoxy high gloss. Roll and tip or just use a high quality brush. It is not hard and you will be impressed with the look.

pete

 

[Bacchus]

I wonder if a PO used one of the liquid floor waxes to "put a shine" on oxidized gel coat? Not uncommon to have oxidation above the rub rail and not below. I frequently treat those areas differently. The sun / UV is much less on the lower due to the angles vs surfaces above RR.
I think before I painted or wrapped I would experiment in some areas with a HD wax remover (ammonia, dawn, floor wax stripper?) and some compounds / polishes to see if it cleans it up and removes oxidation?
I have had good luck with Collinite cleaner applied by machine but it might need more aggressive compound,.. only way to know is via experimenting.

 

[ghost]

That doesn’t look like oxidation to me. The suggestion it might be an acrylic based coating or similar fits better. Either way, I suspect you will be compounding it away. Try some straight ammonia and see if it cuts it, at least that’s what I used when my MIL kept applying the floor wax that ‘didn’t build says so on the label’.

 

[Comodave]

Welcome aboard. Maybe try some compound and rubbing it out to see if it comes off.

 

[koliver]

A friend once talked me into using an acrylic floor wax on my gelcoat. Mine never got to the stage yours is, but was on its way. Getting it off was brutal. an aggressive cut did some, but wetsanding was easier and left a better surface when finished. I then tried Colinite polish followed by Colinite wax, but still, after a few more years I ended up painting, as suggested above.

 

[Larry M]

Welcome aboard. Maybe try some compound and rubbing it out to see if it comes off.

Yup or try Magic Eraser in an area. We had some old gelcoat that seemed to go black or moldy in few areas. I have no idea what the stuff is or does but it worked(s) for us.

https://www.mrclean.com/en-us/shop-products/magic-erasers

 

[Bacchus]

Yup or try Magic Eraser in an area. We had some old gelcoat that seemed to go black or moldy in few areas. I have no idea what the stuff is or does but it worked(s) for us.

https://www.mrclean.com/en-us/shop-products/magic-erasers

Here's whats in those "magic" erasers.
They feel like a sponge but they are pretty abrasive so caution on smooth shiney surfaces. Not sure if the formaldehyde and bisulphite provide some cleaning abilities.
https://www.wired.com/2015/09/whats-inside-mr-clean-magic-eraser/

 

[C lectric]

Magic Eraser has a grinding compound. I ruined some other wise nice plastic chairs with them.

 

[caltexflanc]

Magic Eraser has its uses, but you need to immediately wax or put a sealant over wherever you use it.