How to Polyurethane Stair Railings

Fill a bucket with 1 gallon warm water. Add 2 caps full of wood soap. Wet a clean cloth with the solution and wring out excess liquid.

Wash the stair railing to remove oil, dirt and stains from the surface. Rinse the railing with a damp cloth and dry it with another cloth.

Remove old stain and finish by sanding the stair railing with a medium-grit sandpaper of about 100-grit. Move the sandpaper back and forth with the wood grain until the bare wood is revealed. Follow up by sanding the railing surface with 150-grit, then 220-grit sandpaper, to remove all traces of finish and smooth out any scratches or flaws in the wood surface.

Clean up the wood dust by vacuuming your stairway with a hand vacuum. Dampen a clean cloth with water and wipe off the stair railing to remove all traces of dust. Dry the railing with another cloth.

Tape off any hardware as well as the balusters and newel posts using painter's tape. Cover the stair treads with a plastic drop cloth and secure it in place with painter's tape.

Apply your desired wood stain by wiping it onto the bare wood with a clean cloth. Follow up by wiping the wood with a dry cloth to remove drips or excess stain. Allow the wood stain to air dry overnight. Apply one to two more coats in the same manner if you desire a darker finish.

Paint the first coat of polyurethane on the stair railings using a foam paintbrush. Allow the clear coat to air dry overnight.

Smooth out any drip marks or blemishes in the first coat of polyurethane by sanding it with 220-grit sandpaper. Vacuum the dust and wipe the stair railing with a cloth.

Repeat Steps 7 and 8 for a second and third coat, if desired. Use 400-grit dry/wet sandpaper to remove flaws between the second and third coat.