I've had a few instances of the gel wrinkling in this way... In my case I'm almost certain it's when the paint on the buck isn't good quality and reacts.

As Matt says, the gelcoat would still be fairly green at that time and thus would still get a good bond.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

So you can apply a second coat of styrene based gelcoat even though its pretty much cured? I thought it had to be just tack free so it will bite.

i am unsure if this is related but am tossing it out on the table so to speak. i had some polyurethane paint
for the engine bay of our F16 jets, and it was sprayed on cold sheetmetal and wrinkled immidiately. it did cure
and i wet sanded it smooth and fixed it. paint and epoxy obviously are not the same, but when things are made for
a certain temperature range and you get on that borderline--weird things happen,
 my thought is , perhaps cool work conditions and cold materials could be part of the problem?

CarbonFiberCreations

The other thing I would suggest is are you sure you mixed thoroughly. Mix well in one cup and then transfer to another cup and mix again with a new stick. I used to get all kinds of problems like you describe until I made this my practice.
Hope this helps.
Fred

i think what he means is modelling clay or wax used on the plug.  ie if hes reused the clay off an old plug, it may well pick up contaminates.

I think I am starting to notice, if your clay you use for making the mold has been used a few times before it seems to be more susceptible to worming or alligatoring. Must have something to do with the clay absorbing something.

Hey Don,

Where are you thinking clay is involved in this (do you mean the mould making putty? - if so, how can you use that a few times??)

I still wonder what would happen if I had moved faster with the two coats, giving only a couple hours between each, then going straight to the coupling coat on the same day. I read a post from a guy that did the whole thing in one day so I guess it would be worth a try. Maybe on a smaller part.                                                    

Hi Caden, Im glad the new attempt went much better. RE the above, I'm convinced it will go badly but give it a go for your own peace-of-mind and just to prove that undercuring is where the problem lies. A double application is favourable over a single so it's worth figuring it out. We get lots of feedback about how slow the Uni-Mould gelcoat is, especially at lower working tempertaures, so use the higher catalyst level and ensure plenty of cure time between coats to avoid the reaction.

--Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

I think I am starting to notice, if your clay you use for making the mold has been used a few times before it seems to be more susceptible to worming or alligatoring. Must have something to do with the clay absorbing something.

 



If Brute Force Isn''''t working your not using enough...

Attempt number 3 was much better with no wrinkles. I went for just applying one coat of gelcoat however when I got it out and polished up, you can clearly see several places where the brush strokes were too thin. I hope this won't be a problem for using the mould with my prepreg. For my fourth attempt I went back to doing two coats of gelcoat although this time I let it cure overnight after each application. It came out with only two very small wrinkles this time so I think I've got it worked out. I still wonder what would happen if I had moved faster with the two coats, giving only a couple hours between each, then going straight to the coupling coat on the same day. I read a post from a guy that did the whole thing in one day so I guess it would be worth a try. Maybe on a smaller part.

Matt,

Thanks for the help. It's funny 'cause I was going to try moving quicker for my next one and apply the coupling coat after 2-3 hours. You had it right with the conditions I had it curing in. It was around four hours between coats of gelcoat. For my third attempt I am going to try just one coat of gelcoat and once again leave it overnight. My second part came out this morning with more holes than the first one so I'm working now to get them filled and sanded down. A little elbow grease and hopefully it will look okay. I'll let you know how the next one turns out...

Caden