Gelcoat problem

[McDog]

I just sanded and put a layer of west marine finish gelcoat on the bottom of my hull. It seemed to work well and looks good except:

it will not dry/cure on the area where I did a hull repair with uscomposites epoxy/cabosil. Is it a epoxy/polyester thing? Can I wipe the area off and prime it, and reapply it to get it to work? :dunce:

 

[waterfreak]

I'm assuming that it's your xp your fixing and not your SJ (cause that's SMC not fiberglass) Something about epoxy and gelcoat don't go together well. A good primer should solve the problem.

 

[WFO Speedracer]

Did you put a wax additive in the gelcoat before spraying it ? You either have to do that or spray over the GELCOATED area with PVA to get gelcoat to cure properly,gelcoat will not surface harden when exposed to air,also I know you did not say this but what did you use for a fairing compound,I have seen bondo used on boats before and gelcoat will not cure on top of bondo,don't ask me why they are both polyester based.You can use a primer but it should be a two part epoxy type of primer.Also make sure to sand with at least 220 grit if you want gelcoat to adhere properly.

 

[hangtime]

All you need to do is spray it with a PVA (mold release)to get it to dry .
I did the inside of my SJ that was reinforced with epoxy and it stuck very well ,but I sprayed it like the directions said to do ,and it cured mint .

 

[2006superjet]

same thing happend to me i saned the hull brushed on the west marine gelcoat i let it air dry in the sun for a good 5 hrs. and it didint dry to anypart that i epoxyed around the tubbie reinforcment. do i just sanded it all down and left it it will all scratch off after a few beaching. gelcoat is stayting on fine so far. its a nice layer of protection kinda like rhino lining. i wet sanded it and then cut it with a compound then wax. about it not dryiing to the parts try the 2 part primmer or the wax stuff after you brush it on.

 

[WFO Speedracer]

Also gelcoat is very particular about the amount of hardner and thinner you use in it,I try to measure mine accuratly when I spray it,anything less than 1 percent MEK and it will not harden properly,the amount of MEK used depends on the ambient air temperature,at 1 percent it needs to be 70 degrees or above,at 3 percent which is the max ,you can get away with spraying it at 50 degrees.It is exothermic so the more hardener you add the more heat it produces to cure.20 percent thinner is max,thin with styrene if available or use patchaid,lacquer thinner and acetone will work but nota as well .

 

[astral]

Gel coating a small area is a bit$$.You can cover the repair with pva plastic wrap / just about anything that will create a barrier from air.
If the repair area is small Alot of times I will not use gelcoat as it is diff to feather the repair on small area's.I will use base coat clear or a 1k.
You can color match with white and some grey,just tent the white with the grey until it is spot on..Alot easier to sand ,feather into the surrounding area and bonds without hassle....

 

[McDog]

It was on my superjet. I brushed it on. It cured just fine everywhere but over the epoxy/cabosil.

 

[WFO Speedracer]

DAMNIFINO I worked at the Ski Nautique dealer for a cpl of years,we used West System epoxy extensivly on our repairs and gelcoated over that,I never had a problem with gelcoat sticking to epoxy,is there some possibility that the resin did not cure fully?

 

[wydopen]

i believe every gelcoat kit ive seen (actually oxnard111 was looking for one) says WILL NOT work with epoxy resin???

 

[McDog]

So I can spray PVA on it OR wipe it off, prime it(rattle can?), and reapply?

 

[#ZERO]

You can clean that area off with some styrene to remove the gel coat.

Gel coat doesn't seem to adhere too well with epoxies.

If you're going to reapply it, I'd try mixing it a bit hotter around 2% to 3% in that area and use a heat lamp for a fast cure.

 

[McDog]

us composites said to sand it down as best I could, use a polyester primer, then recoat.

Thanks for the help guys.

 

[McDog]

I checked my hull today and the gelcoat over the epoxy is no longer tacky. It seems just as hard as the rest. Go figure?

 

[WFO Speedracer]

Personally I think the epoxy may not have been fully cured,sometimes it takes days to cure fully.If it is not fully cured the gelcoat put on top of it would not cure properly either.Epoxy and gelcoat will cure eventually if given enough time.

 

[McDog]

That epoxy was weeks old---definitely fully cured.