Gelcoat problems

Hey everyone. I sprayed gelcoat on the hulls of my 1981 Hobie Cat yesterday. The problem is that 16 hours later it appears to have hardened very little (can still put my fingerprint into it easily). I could have undercatalyzed it, this is what I thought I measured out:

10 oz gelcoat with pigment
1oz styrene with parrafin wax for surfacing agent
3cc's of MEKP

85F and boat was in the sun for 5 hours before dark

Its possible I messed up a measurement, but I got at least 1-2ccs MEKP in there. If gelcoat is undercatalyzed will it ever harden? And this layer isnt as thick as Id hoped and was going to spray a second coat over it anyway. After the wax "fully curing" I was going to sand this coat before spraying the second. Could I spray the second coat, since the first is still tacky, and could that help cure the original coat?

 

Update. It is 24 hours after spraying, and it does appear to be getting harder but very slowly. There are spots where my fingerprint doesnt stick, or I have to puch very hard to get it to make an impression. But I can still easily indent it with my fingernail. Any hope?

 

Spraying more gelcoat over uncured gelcoat will not help the first layer cure. MEKP does not diffuse very well in the resin; the resin is too viscous for it to mix freely. Hence why it takes so long to mix the stuff in the pot, and why you have to keep mixing for a couple of minutes after you think it's as good as it'll get. The catalyst can't diffuse into the resin on its own at all once the resin has begun to kick (I've tried it).
Your best bet is probably to try leaving it for a few more days, making sure the humidity doesn't get too far off normal and the temperature doesn't drop too cold. It may just take a few days to harden. If it's not rock-solid in a few days, though, you may have to scrape it off and re-do.

 

OK thanks Marsh. Is there a good way to scrape it off? At least some of the gelcoat is curing, although I am not sure how complete the cure is. There are definitely spots, however, that are still basically "wet." I amassuming I should sand the places which have cured since I used surfacing agent before applying a second coat?

 

wipe the area that u sprayed with a rag soaked in acetone and rub hard then get another clean acetone rag and rub again this should remove most of the uncured gel, wait a 1/2 hour and sand the area down for respraying, how well did u stir the mekp it sounds like u didnt mix it well, also 10% wax is a little high try 2 to 3 % , if you have to much wax the gelcoat will have a rubbery feel to it, wax first and stir for a couple of mins , then add the mekp and stir for a couple of mins . under mixing is the sound of your problem

 

Thanks Jack. Yeah I actually thought that too, some areas seem to have the wax coming to the surface as it should and cure while others are still "wet" so you could be right, however it still seems like the entire surfce is undercured. The 10% is the styrene with wax in it so it should also act as a thinner and surfacing agent. Is that still a bit high? Thanks for the rag tip ill give it a shot.

 

3 cc's of catalyst to 10 oz's of gel coat is about 1%, you need around 2% for gel coat to cure correctly in a thin film, if it was 1 or 2 cc's then it was extreamly under catalyzed. Plus if your repair was done in the sun, then frequently the wax will not come out of solution and rise to the surface, this leaves the surface tacky. Most of the curing is done in the first few hours, if it's not cured after 16 hours in warm weather, then it will never cure correctly. It's best to clean it off with acetone and sart over.

 

thanks again ond

 

everything marsh has said is dead on,,but just need to REALLY STRESS that direct sunlight is bad,bad not saying that was your original problem, but never ever try to cure gel-coat, fiberglass, anything really, in the direct sun. heat is good but not that intense.

 

Even at 1%, it will eventually cure. It may take a long time but it will set up eventually.

 

Unfortunately there's a big difference between eventually getting hard and a proper cure. Low levels of catalyst can cause problems throughout the life of the product, common problems are poor weathering, poor water and chemical resistance loss of gloss, color change, chalking, poor surface profile, soft surface, cracking, staining, poor abrasion resistance, and blistering to name a few. The same goes for under catalyzed resin, over catalyzing will result in similar problems.