Varnish - How Many Coats?
By Don Casey
Revised by BoatUS editors in April 2012
The following coating schedule for applying varnish is offered as guidance, not gospel, but following it will nearly always yield a head-turning finish.
Coat 1 —Thin about 50% with the specified thinner. This is the sealer coat. Allow to dry overnight.
Coat 2 —Thin 20% with specified thinner. Do not sand sealer coat before applying coat 2. Let dry 24 hours.
Coat 3 —Thin 10%. Apply over coat 2 without sanding. Let dry 24 hours.
Coat 4 —Sand coat 3 lightly with 220-grit paper. Apply varnish full strength. Allow to dry over at least 2 nights.
Coats 5 & 6 —Same as coat 4 except sand between coats more heavily to “plane” the surface smooth. Flat surfaces may be sanded with an orbital sander.
Coats 7, 8, & 9 —Sand by hand with 320-grit paper between coats. Apply varnish full strength, taking extra care to avoid runs and sags. Allow each application to dry over at least 3 nights before overcoating.
Coats 1 through 6 can be your finish varnish or a less expensive formulation, but do not use hardware store varnish. General purpose varnishes are typically too brittle for marine use. In hot weather coats 4 through 9 may require a small amount of thinner to keep the brush from “dragging.”