I had a set of molds for something once that were white gelcoat. One day out in the sun I was spraying in the blue PVA, building it up a bit at a time swapping between halves. Went upstairs to let it all dry and when I came back the PVA was dark blue and peeling up in the corners from the shrinkage.

Being white, out in direct sunlight and swapping between halves, my eyes were playing a "white balance" trick on me and I couldn't see how much I was building it up. Coming back after a break I saw how much I had sprayed in and it was beyond redonkulas (Shrek reference). I've never tried the foam roller thing, I'll give that a go next time..