Both actually.
I was also thinking about the superglue i was using as the likely culprit. Paint and varnish didn t cause warping on that 75mm base (but i did varnish it first with a thin layer and let it try for a couple of days too, before applying primer)
Warping only occured after applying static gras with quite a bit of superglue. So it must be the drying and likely contracting superglue that caused it.