If you have ever built a Bar Mills kit, they recommend priming with a grey color (for wood kits, do both sides, to minimize warping). The paint with the topcoat. After it dries, lightly sand the topcoat to reveal some of the grey undercoat. This is a rather simple “weathering” technique, and could be used on plastic structures, as well.
Everyone has their favorites! I like Plasticoat gray automotive primer. I’ve used it on brass steam and on plastic diesel shells after I’ve put on a lot of brass parts such as handrails and Pennsy style trainphone antennas. After it drys you can use Scalecoat II or Floquil paints over it. With a spray can you do have to be careful not to build up too much paint and to be sure you get all the nooks and crannies covered. The primer is really thin and detail does not suffer.
You can use spray can primer but if you aren’t carefull you will lose all your details in your model. It sokay for non-descipt items like propane tanks, water tanks, roads etc., but I’d stay away from it for brick walls, building fronts etc., ESPECIALLY if you model in NScale. The compounding of spray can primer makes it much heavier with particulates compared to spray paint from your air brush. If you know how to use an airbrush I would stick with it.
Mike Langford
SOO Line 1966