So I'm switching to prepreg for my helicopter canopies. Need to make a female mold that can handle 120c. Because of how the plug is made, the mold can't be made with prepreg. I mill my plug out of mdf, spray with duratec surface primer, then sand/polish. The duratec is only specd to handle about 95c so that's why I can't bake a prepreg mold on it.  I ordered some room temp cure high temp tooling epoxy and high temp surface coat. Plan is to brush the high temp surface coat onto the plug  (after frekote is applied) then do carbon fiber wet lay on top of that to create the mold. I will let it cure at room temp, then remove it from the plug and post cure the mold in the oven. Will this work? Or is it an issue to post cure a mold after it's been removed from the plug? Reason I ask is, I once post cured a cf sheet that had a perfect glossy surface. During the post cure, the surface finish got much worse. Had visible print through and lost it's nice gloss. Is this gonna happen to my mold if post curing after removing it from the plug? I could at least post cure on the plug up to 80c or so if that helps, then remove it from the plug and cure the rest of the way. Thoughts?

have you considered using tooling prepreg? It cures at 50-60 degrees then post cures up to 180 degrees.

Tooling pre-preg doesnt like Duratec, I have tested that myself and don't recommend trying it.

There is no problem at all with post-curing a mould off the plug, the trick is to do it extremely slowly. If you can do any sort of elevated temp cure on the plug then this definitely helps, even if it is only 40C; 80C is even better. Once off the plug, you need a very controlled ramp rate of 0.1° per minute, with soaks every 10° for at least a couple of hours. Remember that print through is a product of low resin content, so a resin infused CF sheet is very likely to suffer a lot of print through. A wet-lay mould with a surface coat should see less print-through, but you also want to maintain dimensional accuracy, so a slow ramp rate is very important.

handy to know tooling preg and duratec dont mix, ive not had the joy of mixing the two together! 

Yeh it was a big disappointment for me as Duratec is my go-to pattern coating. The XT135 definitely needs to be cured in contact with epoxy though, it just pinholes badly against any polyester or vinylester surface. It's just much easier to wet-lay an epoxy tool and get a perfect surface finish off the Duratec, so I've virtually given up on the XT135 - even though it's such a joyful way to make moulds 😔