putting on primer


New Hunter
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?

Mutley Out


Active Hunter
Welll it is cardboard after all. If it is the kind with no top layer then it will act like any paper in contact with fluid. You may try to sand it a little but I'm not sure if it will help.



In this case the primer is acting like a sealer, as it would with wood. You can lightly sand it and do a second, perhaps third coat of primer. Eventually it will stop being hairy.


Sr Hunter
Yeah, painting unsealed cardboard or paper is tricky. I would recommend letting it dry thoroughly, then sand it down well before going any further. You can try sealing it with some kind of PVA glue or a similar product. PVA glues are ones like Elmer's or Mod Podge. Mod Podge is what people use to seal jigsaw puzzles. You can get it (or something like it) pretty cheap at places like Michael's or Hobby Lobby. I'd try brushing on a couple of light coats of that with some of those disposable foam brushes. Don't lay it on too thick or it can run or drip, and that will mean more sanding.

But if you keep going without sealer, it's going to take an awful lot of primer to get things smooth. Good luck!


Jr Hunter
Have you tried applying resin to cardboard the sanding smooth? I know that work with my Iron Man suit I did a while ago

Sent from my iPhone
Resin on carboard is OK for shiny things but not for dull paints like the jetpack...

I recommend mod Podge as that was the best solution for me. Put on about 3 good layers of it and them sand it down with high grit sandpaper. Then just scrub it with a red/gray scotchbrite pad from the dollar store...

Hope that helps:)

Sent from my KYOCERA-E6560


Jr Hunter
Oh, didn't know about Mod Podge.
I've spend hundreds of hours sanding bondo from my bucket to get it nice and smooth...
Could I just have applied that over the smooth cardboard from the beggining? :c