Step 1
Sand the surface of the wood smooth with 180 grit sandpaper. Follow the grain of the wood when sanding. Wipe the dust off with a tack cloth.
Step 2
Apply a thin coat of a water-based latex exterior wood sealer to the Douglas fir with a nylon paintbrush. Follow the grain of the wood and use long, even, overlapping strokes. Do not apply the sealer when the temperatures are below 50 degrees Fahrenheit.
Step 3
Let the sealer dry according to the package directions. You can apply an additional coat if the sealer contains a stain and you want a darker finish. Let the sealer dry completely before using the wood.