After some research on the forums here, I still find myself asking a question about primers. I have used el cheap spray can primer on a significant number of structure projects (HO), but am now in the engine shell and rolling stock repainting business for a while. With the structures, I found that the gray el cheap primer-used carefully, so that I didn’t overcoat the target surface, was fine. Now, with the more subtle details on engine shells and car bodies, I wonder if I should stop my frugal ways in this regard and buy stuff like Model Master military light grays,etc. I read that the formulation of the model spray paints is supposed to be finer, in terms of particulate size, than the generic auto or general purpose primers, but if I got good results on structures, why should I not continue that way? Any thoughts? Cedarwoodron
Sounds like my experience. While I have used CHEAP primers before, I’ve taken to buying brand name primers (and finish coats, too). They work great and are way cheaper than model paint spray cans. I can’t say that I’ve had a model ruined because of a spray can paint problem, but I’ve managed to create FAIL myself far more than once.
For priming metal, you cannot beat the auto primers in spray cans. That stuff is sold to working car mechanics who need it to stick to some what greasy, not that well cleaned auto bodies. The major paint companies do expensive R&D to insure that their product has the best “stick-to-metal” properties known to man. Lay it on in a thin coat and it’s the best stuff you can get. Stick is what you want, any peeling or chipping looks a whole lot worse than any other paint flaw.
The model paint companies offer stuff they call “primer” and it has the right look to it. There is no way for us modelers to know if it will really stick to metal as well as the stuff made for the pro’s does. A good organic chemist might to able to tell, but I ain’t an organic chemist.
Priming wood, is a totally different problem. Everything sticks well to wood. The purpose of a wood primer is to fill the grain, so the grain won’t show thru the finish coat. The soft grain soaks up more paint and takes on a deeper color than the harder grain, and the color contrast allows the grain to show thru the paint job. You want a transparent primer on wood. I like shellac, but lacquer and varnish work too.
Plastic only needs primer to even up the color of the substrate. The different color plastics used in a project, the bright white splotches of filler, and printed trademarks can show thru finish coats, especially the lighter finish coats like yellow. A coat of auto primer will cover all this, giving a uniform underlayer to give the finish coat a uniform appearance regardless of the state of the plastic substrate.
Since I have a great paint remover in the form of a purple spray solution called “Super Clean” (Ace Hardware and similar stuff at Walmart) that does a wonderful job of paint removal on styrene diesel shells, I went ahead and gave the upper shell a careful spray with my el cheapo Walmart primer. The primer laid down very nicely over the more delicate details of the vents and access door latches. So, that solved the cost issue. Now… The lower walkway/wheelbase outer housing seems to either be a combo of Delrin and Styrene, or all Delrin. I know that the handrails I cut from the walkway piece (in planning to replace with metal wire rails) were Delrin, yet I was able to use regular Model Master styrene glue to attach some small parts to the sides below the walkway deck. Is such a combination of dissimilar plastics (acetal and styrene) possible? At any rate, I wonder if the el cheap primer should be applied directly to this lower piece, given the different plastic material nature of it, or should I do some sort of alternate surface prep. I clean parts with dish soap, rinse well, air dry and then re-clean with a lintless foam pad and 91% alcohol, then air dry again before any painting of bare surfaces as a general procedure, but want to make sure the primer stays on the acetal plastic well. Any further advice is appreciated.
I like & use the zinc chromate by Floquil. Don’t know if it is the same formula, but the military requires it under all top coats on steel & aluminum (at least they did when i was working) By thinning it down & using 25 lb pressure, you won’t cover any detail.