I am constructing a mold using a plug (EPS fiberglass / epoxy resin) coated with Duratec grey primer. I then lay it onto of a sheet of plexiglass (as a parting surface) and create a fillet with yellow wax. I like the working characteristics of the wax. I then prepare the plug with Partial #2 and Partial #10 (sprayed). I apply my tooling gelcoat with a sprayer at about 20 mil thickness and back it with several layers of chop strand.

After demolding, I have noticed a wrinkle like texture over and adjacent to the yellow wax. I can't figure out what is causing it. I wonder if it might be thermal mass heating from the gelcoat accumulating in the crease between the plug and the parting surface. It looks fine externally once it is tack free and before I apply the chop strand. I would appreciate any thoughts that anyone might have to address this. 

My shop is between 75 and 78 degrees F and it is very dry (low humidity). Altitude about 4800 feet.

Cheers!

Yeh you've probably answered your own question. The wax does struggle above 50 degrees, which could be a possible temperature of the curing gelcoat.

Unfortunately if this is the case then there isn't a whole lot you can do about it other than just sanding the fillet smooth after demoulding. I've experienced this quite a bit, and I usually just use a razor blade facing backwards to flat the wrinkled areas of the fillet down, then hit with 1200 and compound with the rest of the mould.