- Bare Wood: The wood should not be too dry or the varnish finish can lose gloss, crack, and check. A suitable moisture content is 15-20%. Make sure the surface is clean and dry before sanding.
- Previously Varnished, Good Condition: Remove surface contamination before sanding. There is no need to remove the previous varnish if it is not peeling or cracking. The exception is if you are going over a single-part spar varnish or urethane with a two-part varnish—the single-part finish must be removed first.
- Previously Varnished, Poor Condition: Remove old varnish in poor condition and start from bare wood. You can remove old varnish with a chemical stripper or a heat gun. A heat gun is especially effective on curved or irregular areas. Be careful not to expose fiberglass, portlights, and hatch composites to a heat gun's excessive heat. Be careful not to burn the wood.
- Stained Wood: Be sure the stain is totally dry before any varnish application. Best to test a small scrap of the stained wood with the varnish over it first to be sure there isn't a reaction.
- Epoxy should be fully cured 5 to 7 days, depending on product and temperature.
- Wash with water and scrub with a Scotch-Brite™ pad to remove any possible amine blush.
- Sand any runs or rough spots smooth starting with 80-grit sandpaper, then 150, ending with 220 grit.
- Vacuum any dust, and clean well with acetone or denatured alcohol.
- Generally, it is not recommended to apply a regular solvent-based spar varnish over polyurethane finishes, but you can apply a polyurethane over a spar varnish in good condition.