Maybe this does not belong to this thread, but my fender is now stuck in the mould badly I got the flanges out, but the paint is sticking to the mould. I'm SO annoyed. I used plastic wedges to pry it out, but the fender just starts to bend.  I also tried air pressure, and high water pressure washer without luck.  Could I heat the fender? Ot could I apply thinner in between the mould and the part?

I used this release wax: https://composite24.co.uk/mold-wax
I had the mould some hours in the sun about 55 degrees C, could that affect to the release wax not to release? I'm afraid to use it again!!

Wax release agents are usually known for their problem with elevated temperatures. The one in your link explicitly says that it's for room temperature use only. And the sun heats things up very unevenly. It could be that some spots got even higher than 55°C.

Yes, I can see that now. But how can I remove the fender without bending or breaking the mould?

Oh dear... This is heartache.

The heat won't be the issue if the gelcoat cured at room temperature. If you accelerated the cure of the gelcoat by applying heat before it cured, then this could mess with the release. But once already cured, the gelcoat can't then bond to the substrate if it is later heated. So I daresay the coating on the pattern was not compatible with the gelcoat and it has reacted and stuck. Either that, or an application issue.

None of that really helps you now, but unfortunately there isn't much you can do now. Heat may help, as polyesters break down quite quickly with heat and you may be able to damage the gelcoat enough to break the bond. Realistically I think brute force is really the only thing that is going to get the part out, so chances are it is going to get pretty damaged in the process.

Gelcoat was cured in a room temperature (about 20C). I didn't heat it. So then it must be the paint I used. I'm so pissed right now

I will try to heat it and then maybe add some thinner to break the paint.

I got the fenders off! They were super tight!! The paint wasn’t stuck as I thought. I used wooden long wedges to pry those off. First I heated the fenders but it didn’t help.

So it released ok but was mechanically tight?

Yes, but I don't understand why. The fenders go in and out in the mould easily now.

It looks quite tight on some of the curved wing edges -  but hard to see properly so may just be the photo's.

Also you can get vacuum that is hard to break sometimes.

Also consider possibly the resin hadn't fully cured at first attempt as epoxies in particular, grip the mould surface if a little bit green.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant