It's probably a noob problem and question but I started building a jetpack from sintra & cardboard. I've filled the gaps with Motip Fine Putty and after sanding it all, I put a spraycan primer on top of it. And here comes my problem( if it is one?):
When spraying the primer on the cardboard, the cardboard takes in a lot of primer and the surface is kind of "hairy". Is this normal or how do you solve this?