Clear Gel Coat sticking to mold?

General Composites Discussions Products Talk
#1

I think I already know the answer to this one but here it goes.

I did everything exactly as I always do- only difference is the temperature is much colder. I cleaned the mold, hit it with some semi permanent mold release, wait around an hour, sprayed my clear gel coat into the mold (10 drops of MEKP per oz.) and I let it sit until the next day. Came back, made sure the gel coat wasn’t tacky, laid my carbon in the mold, vacuumed with infusion and let it set under a heat lamp. It took forever to cure and when I pulled it from the mold just now, a huge chunk of the clear gel coat stuck in the mold.

It doesn’t seem to be a problem with the semi permanent mold release that Evan sells because you can scratch the gel coat out with your finger and the mold looks like it’s ready to go again.

Is the problem with the colder temps? If so, how should I be mixing my clear gel coat?

#2

What resin did you use for the infusion process? How hot did you put it under the heat lamp? If it’s cold, I’d kick the MEKP ratio up a bit. 2% is by the book but I’ve gone up as high as 10%. Especially when I have to thin it out with acetone.

#3

I used the System Three SB112. Heat lamp was keeping it around 85 degrees. I talked to a buddy of mine that showed me how to vacuum infuse and he’s saying I had to have mixed the epoxy wrong. :oops: Evan, if I mixed 2 parts hardener and 1 part resin on accident, would the epoxy even have held onto the gelcoat in some spots on the part? Most of the part looked perfect. It’s just the one spot in the middle that didn’t quite make it :smiley:

Thanks again for all of your help,
Danny

#4

did you use an epoxy top coat or an poly gel coat? If you used a poly that is probally your problem right there. If you are using epoxy resins you want to stick with epoxy throughout.

#5

No EMI it should be fine. Epoxy will bond to cured polyester but not the other way around. Also SB-112 is specially formuluted to bond with polyester resin either way.

Danny, if you mixed 2 parts hardener to 1 part resin then the whole thing should be really soft. I’m thinking that you got the correct ratio but you didn’t mix it well enough or you might have over cooked the resin in that one spot. 85F isn’t hot at all though so I’m not sure what went wrong there.

#6

ahhhh yes you are right, I get those to mixed up all the time!!

#7

When you say “Overcooked”, do you mean too much heat in one spot from the heatlamp? I’m generally mixxing for around 2 minutes and scraping the sides as I do so- being careful to not get any bubbles in the epoxy. Should I mix longer?

Temp is around 60 degrees today so I’m going to set up another part and leave it until I get home from work tonight.

Also, Evan, did you know an exact time and date yet on picking up that bleeder ply? The company wants to know.

Thanks again,
Danny

#8

Precisely. I’ll confirm the time with you via email. It’ll be tomorrow.