Oak features an open-grain pattern that takes stain well. This hardwood offers a warm golden-brown finish that flatters a classic staircase. Because oak is relatively expensive and prized for its grain, it rarely is painted. Instead, an oak staircase will benefit from a clear coat finish, with or without the addition of wood stain. You may stain and sand the staircase by hand, but for the best finish, you'll need to spray on the top coat.
Sweep and clean the staircase to remove tracked-on dirt. Scrub stubborn mud off with a stiff nylon brush and soapy water and let the wood dry completely. Apply wide painter's tape to adjacent walls to protect them from stain and overspray. If you're finishing a staircase in an existing room, cover the floor with a dust sheet.
Sand the staircase with 120-grit sandpaper or foam sanding pads. The pads conform to the contour of rounded balusters, making it easier to sand them. Sand only with the wood grain.
Vacuum the room, and wipe down the entire staircase with a tack cloth to remove dust. From now until the final coat of wood finish dries, maintain a dust-free zone by restricting foot traffic in the immediate area and by keeping adjoining doors closed.
Apply wood stain, if desired, to the staircase. Start with the balusters, brushing on an even coat of stain with a 2-inch natural-bristle brush. Leave it on until the oak reaches the desired shade. Use a 4-inch natural-bristle brush on larger areas such as stairs and risers. The risers are the vertical sections below each step. Wipe off the excess stain with absorbent rags.
Stain the handrail next, followed by the wood trim on the sides of the stairs. Then stain the stair risers. Stain the treads last, working from the top down. Wipe them down with tack cloth once more before applying the stain. Allow the staircase to dry completely. This might take 24 hours or longer.
Sand the oak staircase again to smooth out wood grain that might have swollen during staining. Use 220-grit sandpaper and sand very lightly. Run your fingers over the surface of the wood to check for rough areas.
Spray on the wood finish. You'll get the smoothest finish by using an airless spray gun to apply multiple thin coats of varnish, shellac or polyurethane to the surface of the staircase. Slip protective shoe covers over your shoes to prevent getting dirt on the treads as you work.
Start spraying at the top of the staircase and work downward, coating the risers, the treads and the inside section of the balusters as you step down. Cover every bit of oak possible from your vantage point of standing on the stairs and stepping down backwards.
Use a ladder or scaffolding to spray the upper portions of the outside of the staircase trim and balusters. Let the entire staircase dry completely before adding one or more additional coats.
Brush an additional coat of the same wood finish product on the surface of the stair treads. The wood here needs more protection because this area sees the most traffic. Use a 4-inch natural-bristle brush and apply an even, thin coat, brushing in the same direction as the wood grain.
Test the airless spray gun on a piece of scrap wood to get the hang of it before spraying the staircase. Open a window for fresh air.
Rags used to wipe off stain should be dried in a single layer on the ground and then thrown away outdoors to prevent spontaneous combustion.