My usual method, which gives good results:
1) sand model/balsa parts ( remove big lumps, glue lines etc )
2) Leave in warm place over night ( airing cupboard or something similar)
3) Paint with sanding sealer ( which is just dope with talcom powder in it, is fine just to use dope )
(note - if it's a really "grainy" piece of wood, or I'm dealing with a lot of edges, then I will thin the Sanding sealer down with cellulose thinners so as to get it sucked in deeper)
4) Sand down ( i generally start with 150 grit paper, then 240, and then perhaps 360 if needed )
5) If finish is still rough, or you want another coat, repeat steps 3) and 4)
6) Prime with hi-lift primer ( i.e primer that fills gaps - yellow stuff is best as has most talc in it )
7) block off with 240 grit so that only depressions remain primed
(note 2- any large depressions can be filled with car body filler and then blocked off again - smaller depression can left for the next coat of hi-lift or abandoned if very trivial )
Prime again
9) Block off with 240 grit and then 480 grit
10) Paint
Result looks identical to metal. There is a LOT of sanding to do, but remember that 90% of the quality of the paint job is about getting the preparation right.
Absolutely no need for cardboard, but it won't hurt if it's on already. It sounds like a way to hide any imperfections.
for paint, use arcylics, and then let them dry properly. I use "Matte Varnish" in a spray can from Games Workshop, as the final coat as this is totally waterproof, but specially designed to allow you to paint over it again in future if you need to.
Hope this helps.
Steve
