Finishing automotive exterior wood
What modern finishes are best to use on wood parts that go on the exterior surfaces of automobiles?
Your question is a bit succinct. It does not tell me whether you are talking about wood accents, a pickup truck bed or a woody wagon from the golden age of station wagons. However, in an endeavor to answer your question as completely as possible, I will tell you what I was told by Suzy Carr at Wood’n Carr in Signal Hill, California, a shop that restores and builds custom woodies to show-winning standards.
She says that first the wood is sanded totally smooth, and then it is sprayed with a two-part epoxy sealer. After that it is given 10 to 15 coats of marine spar varnish, sanding between coats, starting in the early stages with 320-grit sandpaper and toward the end finishing with 1000-grit and even finer, and then buffing the whole thing to a flawless finish. The process takes a lot of time because the varnish needs a fair amount of time to cure between coats.
If you are doing a wooden bed in a classic pickup you may not want to go to that much effort though. Fact is, wooden pickup truck beds in the old days were made of a very hard southern pine. This was treated with a combination of linseed oil and lamp black, which gave it a semigloss black finish. The skid strips were painted black as well. And then in the 1960s, the bed wood and skids were often painted the color of the vehicle.
Today most pickup truck restorers put in an oak or other hardwood bed in their classics, and use marine spar varnish as specified above, or a polyurethane clear finish. I used RustOleum’s oil-based Varathane 10 years ago on my classic Bowtie hauler’s bed and it has held up well. The waterbased version is not as durable though, and is better adapted to interior uses.
I ordered oak bed wood and sanded it with 320-grit open-coat paper, then dampened the boards with a moist rag to get the grain to stand up, and sanded again. After that I applied four coats of Varathane, being careful to follow the drying time instructions.
Be sure to do the finishing on the bed wood before you install it, and do both sides at the same time to avoid cupping. Carnauba car wax with no polishes in it works well to keep the wood shiny and sealed after it is installed.
But depending on what you need, and how high your standards are, you may want to leave the finishing of your automotive wood to the experts. In that case I recommend Wood’n Carr. They fashioned new top bows for my 1936 Packard, and they fit perfectly and looked right. You can reach them at:
Wood’n Carr 2345 Walnut Ave. Signal Hill, CA 90755 woodncarr.net