Priming Photoetched and resin parts

I have generally not had too much problem painting PE or resin with enamels.   I've had some minor problems using acrylics,  but I think that was largely due to thinning & air brush pressure issues.   Surface preparation is the key.

You may be experiencing problems on the PE associated with grease & oil.  Skin oils are troublesome if you have been fingering the parts.   Clean the PE fret by dumping it in some lacquer thinner.   Swish & allow to air dry.

Oils & release agent can be troublesome on resin too.   Wash the parts in warm soapy water,  brush with an old toothbrush, rinse well, and allow to air dry. 

Good old Plasticote in the jumbo economy-sized rattle can is a good primer if needed.   It is inexpensive and is available in the auto paint department at WalMart or in your local auto parts store.   I routinely use American Traditions Rusty Red Primer from Lowes as my finish color on resin ship underhulls.   I paint the whole ship, then mask off the below the waterline & paint above

I had a tip alittle while back to dunk the PE part in vinigar just prior to painting the acid in the vinigar etches the metal giving the paint something to grip to. I always prime the PE parts first with a suitable matt colour to go with the main colour.

With resin, I recently completed my first resin cockpit and just primed it very lightly with halfords plasic grey primer from a rattle can, just do 2 or 3 light coats rather than one heavy one so as to preserve the details.

I tend to prime using Tamiya white fine surface primer. It is a little expensive, and I think that the other primers mentioned are just as good, at a cheaper price. You'll need to layer the primer in several light coats to get a smooth finish.