Put on gloves to protect your hands from splinters during sanding and harsh chemicals in the finish.
Sand the chairs with a 120-grit sandpaper to remove any rough spots, scratches or other imperfections. Sand with the grain when sanding by hand.
Sand the chairs with a finer sandpaper to smooth it before finishing. Use a 180-grit sandpaper for softwoods and a 220-grit sandpaper for hardwoods.
Vacuum the chairs to remove all dust.
Place the chairs on a plastic sheet to keep finish drips off of the floor.
Apply a layer of primer with a paintbrush if you plan to finish the chairs with paint. Allow the primer to dry thoroughly before painting the chairs.
Stir the finish to mix in any pigments that became separated while sitting in the can or bottle.
Apply the finish according to its manufacturer's instructions. Most finishes require application with a paintbrush or sprayer. Some penetrating finishes, such as tung oil, are rubbed into the wood with a soft cloth. Some semitransparent penetrating stains require the user to apply them with a brush. Allow these semitransparent stains to soak into the wood for up to an hour. Wipe away excess stain with a rag.
For a darker color, more protection and more coverage, apply two coats of finish. Follow the manufacturer's instructions regarding how to apply more than one coat. Some finishes, such as paints, should dry completely before an additional coat is applied. Other finishes, such as penetrating stains, might not need to dry completely. Some surface finishes, such as polyurethane, require sanding between coats.