By Don Casey
Revised by BoatUS editors in April 2012
Scratch through the top coat of almost any painted surface and you will find an underlying primer coat. Primer prepares the raw surface for the paint. The result is a better finish.
It is useful to think of varnishing as a similar two-step process. With varnish we don’t use the term primer, but we could. Varnishing raw wood always begins with several so-called “build-up” coats, and these perform almost the same function as primer under paint. We want the build-up coats, first and foremost, to get a good grip on the wood. After that, we want them to level out the surface, filling the wood’s pores. We also want the build-up coats to clarify the wood, bringing out the beauty of the grain.
You can use the same varnish for both build-up coats and finish coats, but the pros often use a less expensive varnish for the build-up coats. Only color and clarity matter; flow, gloss, and UV resistance do not become an issue until we get to the top coats. For a foot-deep finish, plan on applying 6 build-up coats followed by 3 or 4 carefully applied finish coats.