Newbie seeks gelcoat help!

You guys really seem to have your "stuff" together and I cant get the right answer from my local shop. I have tons of hours into this project with disastrous results both times. I will try to be brief.....

Jet ski that I am restoring. Repaired a couple spots in the hull without incident using polyster and glass, and used Everlast filler for some of the minor stuff and touch up before primer.

I am trying to gelcoat the hull. I have reasonable talent, but no gelcoat experience. Determined to the point of stupidity to learn and do this myself. Here's what I did the second time....First time I think I forgot to add catalyst in one of the gelcoat layers(panicked when I didnt mix up enough and thought it would go off in the gun) and had to wire wheel off the gooey mess, so 8 or so hours minimum wasted. I have a nice shop with a paint booth, keep a fire going at about 65 degrees clean environment.

Started with repairs and got it relatively smooth. Cleaned it with Acetone and then hit it with epoxy primer. MP 170 and 175. Wait 12 hours, Light sand and repeated primer coat again . Primer looked perfect, sprayed with 1.4 tip

Wait 48 hours, Scuff sand with 220, wipe down with dry rag and vac.

First Gelcoat spray with 2.2 tip consisted of:
Fiberlay Gel coat white
Fiberlay styrene polymer 10% to thin
Fiberlay catalyst at 3%. (washington state, high humidity, but fire in shop at 65 degrees)
Looked perfect, waited 5 hours.

Same Fiberlay mixture as above but added 1/2 oz per pint of mixture(per instruction) of Fiberlay surface seal.

It layed down nicely and then......EXPLODED into the ugliest wrinkly old lady skin you ever saw! Not the alligator look of under application but a wrinkle that looks like a reaction or gases trying to get through and wrinkling the sh*& out of the final coat.

I really haven't the slightest about what to do now. My initial thought is to sand it smooth in a day or so after it hardens up, if possible without removing everything. Use the epoxy primer again and paint the damn thing. Hoping to run this by some wiser minds than mine and the guys that have been taking my money for gelcoat and sandpaper. I understand that they are not responsible for making me a master painter-not putting the blame on them, just frustrated.

Any recommendations are welcome. I am quite inclined to scrap the gelcoat and looking now for a fix so I can just move on because I really want to paint the body!

I will try to attach an image and will try to pay it back as I learn more.

 

Gel coat isn't designed to be used over epoxy primer, and epoxy primer isn't designed for use under gel coat. The only primer that is used under gel coat, is a sanding gel coat.

The problem was compounded by spraying fresh and thinned gel coat over layer of not fully cured gel coat.
Without digging into it a bit I can only speculate as to the exact point of failure, but....

When gel coat is sprayed onto a substrate that can be attacked by styrene it can soften and then wrinkle that surface, some products when fully cured aren't as affected by styrene nearly as much as when they’re not fully cured, this includes prior layers of gel coat.

The first layer of epoxy primer was not a good substrate for gel coat, the first layer of gel coat probably had a poor bond to it and wasn't fully cured when you sprayed over it, causing the first layer of gel coat to raise up and wrinkle. This may look different than normal allegation because there is no bond to a mold surface, there would be some bond to the epoxy primer. The other option is that the styrene attacked the under cured epoxy primer and when another layer of thinned gel coat was sprayed it caused it to wrinkle.

Thinning gel coat adds a degree more likelihood that things will alligator because there is more styrene (or some solvent) free and available to attack the substrate. Also the cold weather slows the crosslinking process and allows more time for the newly sprayed gel coat layer to attack the substrate.

Now you run into another issue, gel coat (even polyester resin) frequently doesn’t stick well to this type of composite, it has to do with the method of manufacturing and the fillers in the resin it’s made with.

So using epoxy primer was correct, but it should be used with a top coat of the appropriate paint, not gel coat.

 

Thanks!

Thanks so much. Makes sense and explains why it turned my epoxy primer to goo. With I didn't have so sand that stuff off. Any recommendations for a good paint to use on the hull on top of the epoxy primer?

 

With paints you get what you pay for, the more you pay the longer it may last, and sometimes may be a little harder to work with. I'm not up to date on the current paints, so someone else will need to make some recommendations.

 

Trying it again

Well, here's where I am at so far. Maybe if I get this figured out, it can help somebody else. My local paint shop guru said he has never had a problem with someone using gelcoat over primer exactly as I did it-twice.... However, can't say the same for a jet-ski. Plastic hull with polyester fiberglass repair. So, a phone call to a big time boat repair shop and here is what they both recommended. Both felt it was a reaction, possibly from the styrene/primer/plastic combo, but not showing until it is sealed off with the wax on the final coat.

So, here's the recommendation. Scrap the epoxy primer and the Styrene. Using Orca Composites Vinyl Ester Surface Primer. Sets off with MEK just like gelcoat.

So....Another 4 hours with wire wheel-done
Filled with duralast and ready for sand today after work, maybe primer tonight, gel tomorrow.....