Can I Use Latex Paint? - Model Railroader Magazine

 Primer.  I use primers on metal for the extra stick, and on wood to hide the grain.  I don't usually bother to prime plastic. 

  On metal I use auto primer from a rattlecan which I purchase down at the auto parts store.  Metal is smooth and slippery and getting paint to stick is a problem.  I figure the auto body men get the best stick-to-metal primer that chemistry can make.  I always worry that the "primers" sold by the hobby paint companies aren't as good in the stickitivy department as the stuff used in real auto body shops.  The dark gray auto primer is a fine color for steam locomotives.  

  I prime wood with something clear, shellac, or clear Minwax, or clear lacquer from a rattle can.  The idea is to fill the pores of the wood and prevent the paint from soaking more deeply into the softwood than the hardwood grain.  This prevents the grain from showing thru the paint.  

  On plastic, I  use the red auto primer, where I need a good boxcar red or brick red.  The primer dries dead flat, takes decals well, and covers well (enough pigment in the stuff to completely hide the underlying surface in one coat).  I don't have trouble with the primer eating plastic.  My freight cars and my brick buildings are all done in red auto primer.  The primer serves as the finish coat as well as the prime coat, so I don't think of it as "priming" but rather as "painting".