When you’re done sanding, remove leftover dust on the box—you don’t want that getting stuck underneath the varnish and ruining the finish. Vacuum up as much dust as you can using a brush attachment, then wipe down the box with a cloth lightly dampened with paint thinner. Finish by wiping down the box with a painter’s tack cloth.
Your specific brand of marine varnish might recommend a different varnish to paint thinner ratio. Follow the instructions on the can for the best results. [4] X Research source Be gentle and go slowly when stirring varnish. Stirring too quickly will create air bubbles, which will affect the finish. [5] X Research source
Work in a clean, dust-free space. Dust, hair, and other debris stick to varnish and ruin the finish. [7] X Research source When you’re working with marine varnish, always dispose of rags, sanding residue, and other waste in a sealed metal container filled with water. Items that have come into contact with varnish can spontaneously catch fire, even without an ignition source. [8] X Research source
Temperature, humidity, and the thickness of the varnish can all affect the actual drying time.
If your sandpaper gums up while you’re sanding, the varnish isn’t dry enough. [11] X Research source When you’re done, clear off dust the same way you did when you sanded the bare wood. Use a vacuum with a brush attachment, wipe down the box with a cloth dampened with paint thinner, then go over the wood with a tack cloth.
Some varnishes recommend thinning the second coat with paint thinner as well. Follow the instructions for your specific brand of varnish to get the best finish.
