by Ron Joseph
Can you polyurethane or varnish over painted surface?
Q: I remodel homes and am wondering if it would be okay to paint and handrail and polyurethane or varnish over the paint? The original finish is stain and varnish (very dated color that does not match the new wood floor color). I've sanded the old finish and now I want to paint it a distressed black, but, want to protect the paint from the constant use it will have with a polyurethane or varnish.
A: There word "varnish" is used loosely in our industry and I'm not at all sure what resin system your are referring to. In the "olden" days it meant a nitrocellulose lacquer, but currently it can also mean an alkyd or modified alkyd. Similarly, the word "polyurethane" is misused, because there are true two-component polyurethanes and there are those that are sold as "polyurethanes" but are really modified alkyds.
Since I can't be sure what you have used in the past and what you intend to use, I suggest that you perform your own little experiment. Find an area of wood that is not easily visible to those who come into your house. Apply the coating of your choice to a small area that has already been coated with the varnish The area can be as small as a few square inches. Watch for peeling, lifting, or blistering. If nothing transpires, then you have passed the first hurdle. Allow a few days to elapse so that the paints can harden, then take an Xacto knife or similar and cut an "X" scratch through the paint. Starting at the apex of the "X" try to peel the polyurethane from the varnish. If it won't lift, but sticks, you have passed the second hurdle. Although I cannot guarantee success, because I'm not there to see what you're doing or the condition of the coatings, I am reasonably confident that you will not have problems in the future.
Incidentally, these are the same steps that I would take in my own house.