Wrinkles in gel coat???

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#1

Okay, so this is a new issue, I’ve made several of this part and its sister part in a different mold without any issue. Recently though, the last three parts Ive experienced wrinkles in the edge of the part.

The mold is an old flange less mold, the parts are hand laid with 1.5 mat and poly resin. I haven’t changed anything product or technique wise, I’ve tried changing the dry time of the gel coat between 24-72 hours but I’m getting the same issues. I’ve been mixing the resin a little slower lately as it’s gotten warmer, but this is what I’ve always done in the past. To recap, I’ve had the issue in both molds, and with different batches of gel coat and resin. I’m kind of stumped.

#2

That’s wrinkling from where the layup resin eats into the gelcoat enough to lift it off the mould.

Usually gelcoat too thin
Laid up too soon
Gelcoat not cured well enough, not enough time, not enough catalyst.

If the layup resin is vinyl ester then this is often more aggressive than regular polyester resin.

#3

It’s polyester resin, the catalyst might be the issue. I feel like the gel coat thickness is consistent as I’ve only started having the issue and that practice hasn’t changed. The gel coat does seem very dry before layup (I realize this doesn’t mean it’s nescesarily cured though). I’ll try mixing the gelcoat at a higher catalyst ratio and see what that does for me.

#4

How old is the resin? The issue with the styrene based resins is as they get older they cure slower. So what catalyst ratio and what cure time you used 6 months ago may not necessarily be enough catalyst or time for the gelcoat to cure properly and so it wrinkles when you do the layup.

Often a good idea to do a 25ml test at 2% and time how long it takes to gel. You want it to be gelling at around the 20 minute mark to be sure of a good cure.

#5

Hanaldo, thanks for the tip, the gel time was closer to 25 min at 2% catalyst. I upped it to 2.5% when I sprayed the molds. Previously my ratio was closer to 1% so I’m hoping this was the issue. How long should I allow the gel coat to cure before layup?

Second question now, I’ve been mixing the resin also with that slow 1% ratio so I have enough time to set out and roll my laminate layer down, is that slow cure time allowing the resin to damage the gel coat?

#6

I normally try to let it cure at least overnight if possible.

Second question - in short, potentially. The longer the resin sits on the surface uncured, the longer it has to attack the coating. That said, I’ve never actually had a problem with using a low catalyst ratio for the laminate. 1% is very low though, I don’t normally go below 1.5%. What temperature are you laminating in? And how big is the item you are laminating, can you not get it all down and consolidated at 1.5-1.75%?

#7

Yeah, it starts flashing off too soon if I go much over 1%. I’ve gotten more efficient so I might try creeping back up on the catalyst ratio. The part is a fiberglass seat, the large piece of glass is about 8 sq feet of 1.5oz mat with a couple flanges that take some extra attention, then there are 2 pieces that are about 3 sq feet which arent an issue on time.

#8

Can you mix smaller batches and catalyse it harder? Once it’s in the fabric you should have time to get it wetted and roller before it gels, it’s normally just the mass in the pot that goes off quick.

That said, it really shouldn’t be an issue if the gelcoat has cured properly. I think try upping the ratio for the gelcoat, try to get it curing faster. Let it cure for 24 hours, then give it a go. If it’s still wrinkling up then I’d be thinking about the application thickness and the age of the chemicals.

#9

I’ll give it a go tomorrow. The gel coat will have had about 72 hours at that point of cure time. My chemicals are all pretty fresh. I’ll start at 1.5% on the laminating resin and see how it works out.

#10

There are four scenarios that may cause this alligatoring to occur.
Applying the gelcoat film too thin is the primary cause. This thin layer of gelcoat will lose a larger proportion of monomer to evaporation than thicker layers of gelcoat. The crosslinking process will deviate from the manufacturer”s intended formulation. This undercured gelcoat is then attacked by the laminating resin which wrinkles the gelcoat layer. Applying the manufacturer-specified mil thickness of gelcoat will prevent this condition from happening.
Another scenario of alligatoring is caused by laminating on undercured gelcoat that is the correct mil thickness. This undercure may be caused by: insufficient
cure time, insufficient cure temperature, initiator problems, and compressed air contamination. The spraying process is another cause of alligatoring. Keeping a wet edge is important. This means that the new gelcoat is applied over gelcoat that is still wet, which allows for all of the gelcoat to cure at the same time. Fresh gelcoat sprayed over cured gelcoat will attack itself and can lead to alligatoring problems.
A fourth cause of alligatoring can be the result of exposure to a solvent such as MEKP or acetone before the laminate is applied. The most common cause for this is an equipment leak during laminating operations. Solvent rags placed on the gelcoated surface may also be a culprit.
These above are a few of the causes of gelcoat alligatoring. Once these conditions are under control, few problems will present themselves.

#11

Thanks guys, pulled two perfect parts out of their moods today. I’m pretty sure I’ve been using too little catalyst. So thanks again, I do appreciate the professionals taking time to lend knowledge to a hobbyist.