What should I use as a primer coat if anything on a plastic spinner.  Its white and gonna spray it green (SIG butyrate) for my Chevelle.  The first one I did I just scuffed it with 400 or 600 (dont remember).  Came out OK,  but didnt seem to have real good adhesion.     

Allan,

Back in the days when dependable AeroGloss dope was available, it seemed to be simpler...

A wet wipe-down with A-G thinner both removed any mold release agent, AND, perhaps, micro-etched the surface for decent adhesion with A-G colors and top-coat clear. (Same worked for color doping clear $kote, btw, but adhesion was marginal. Masking tended to lift the underlying coat, yet if done right, could last beyond the expected finish.)

Note: This Monokote Clear, scuffed, finish was about the lightest that could be done! Given: the plastic film added near zero stuctural strengh to the bare bones. BENEFIT: IF the wood under the film was sanded and tack-cloth-ed well enough, the finish compared well with the slow, smelly and iffy buildup of dope/sealer/sanding/dope/sanding/tack-ing/ clear sealing/color doping/ detailing/ top-coating sequence we had been doing for the 25 tears before.

Alas, butyrate shrinks too much, too quickly, for the dope over (micro-etched) film....

And, to day the EPA (Enjoyment Prevention Agency) has issued too many 'Thou shalt Nots...' to prevent us using anything that works, if we are to enjoy the results of our efforts. (NOTE Len - this is not political: it has broadened its impact to all of us!)

Howard,

The EPA didn't address aircraft dope adhesion on plastic spinners in so many words, but they sure have caused changes in the aircraft dopes we can locate and buy. Used as I described, the old A-G dopes and thinnners seemed to give reasonable adhesion way back when. Now any A-G you find is likely to be muchos years old, and from an era when EPA-obliged changes made consecutive batches of dope from the same manufacturer unlikely to be consistent, or even compatible with earlier batches.

As I recall, anyhow...