UV Smooth Prime produced by Poly Fiber provides ultra-violet sunlight protection for resins used in fiberglass structures. It is an excellent filler for leveling fiberglass surfaces and sands easily for a smooth matte finish. It provides superior adhesion for all primer paints.
The UV Smooth Prime has lots of filler that will settle to the bottom of the can while in storage; you must throughly stir the can contents before each use. Do not shake the can to mix as you might do with regular paint; excess air bubbles get mixed in. The bubbles will cause uneven application and pin holes. Do not buy more than you will use in a month; the cross-linker catylist has a short (about 30 days) shelf life.
Poly Fiber instructions indicate spray or roller application. I find that you have to be careful getting runs with the spray application, so you have to do lots of light coats. Roller application with a sponge roller goes on fast, but leaves a wrinkle finish. I have to sand almost all the Smooth Prime off to get rid of the little creases in the wrinkles. I am able to slather on two thick coats with a paint pad or a brush, spray on a mist coat of gray primer for a guage, and then sand with 320 grit powersander. When the gray is gone, stop sanding. Clean off the dust and now the surface is ready for finsh paint primer.

Equal amounts of sanding: Note the aluminum oxide (yellow) has zero clogging.

Sanding Latex Primer
Silicon Carbide 400 grit sandpaper will clog very quickly resulting in lots of sandpaper being used and it goes slow. Aluminum Oxide 400 grit sandpaper makes lots of white dust and cuts fast. One sheet was used for half the fuselage and still ready for more.

ExperCraft is supported by these quality vendors: