Ye Olde Rocket Forum - View Single Post - Primer instead of sanding sealer, what kind of primer?

clhug,

You can buy cheap primer that does a respectable job of filling grain on balsa, and seams on body tubes. While I like filler/primers like Duplicolor, I've had good results using Walmart brand cheap primer, called HomeShades. It's about $1.33 a can last time I bought it. Dries pretty quickly, and sands easily. If you cannot find this one, try Rustoleum Filler/Primer, which works well, it just costs a bit more. Some cheap primers do not sand well, and gum up your sandpaper., so you may have to experiment if you must buy an unknown brand.

Spray it on pretty heavy, and do maybe 3 coats to have a heavy build. If you get a run here and there, no worries, since you need to sand most of it off! The key is to leave primer in the balsa grain and body seams, and not have a thick primer coating on the entire surface. If you do this the grain and seams will never disappear, you'll just see less distinct impressions. Don't sand too deeply though, or you'll tear up the balsa or the cardboard. When you start to see traces of balsa and cardboard peeking thru the primer, you are getting close to the point where you should stop, and prime again. You may have to do this prime/sand cycle several times, depending on the depth of grain and seams. You final cost can be lighter than fill coats, such that you have a uniformly colored, smooth surface for your color topcoats.