Fellstone

I've had good luck with Mr. Surfacer 1500 thinned in the 50% range with Mr. Color Leveling Thinner using a 0.35 needle at 20 psi or so. When I thinned too far (say 2/3 thinner), I had some issues with the primer peeling after masking, but I can't definitively put it down to the thinning ratio -- given the alchemy that is airbrushing, it could have been the phase of the moon. Can't speak to the retarder, though I believe that Mr. Color Leveling Thinner is pre-mixed with a retarding agent.