I getting ready to install harp switchstands on the layout. They are white metal. Do those have to be undercoated before they are painted?
Doug,
A primer coat would be a good idea to help the paint adhere. A switch stand will presumably get handled quite a bit and some wear is inevitable in any case. I like the spraycan primers by Bondo available in grey, rusty brown/red and black. Krylon also makes a good one.
Also be sure the castings are clean. There is often a release residue left on from the casting process.
I agree with Richard , it is essential to clean the item first ,then apply a good primer–if car primer is available , that is a good one to go for .
An interesting aside here , there are model paint primers .I have never come across one that is any good ,
except for the one by Games Workshop . That is made specifically for white metal figures which get a lot of handling , and used properly , it works .
Mike M