For 90 years, the Clear finish on the maple banister had survived the touch of countless hands without ill effect—until a recurrent drip from a leaky roof bleached and discolored the surface, leaving one ruined spot on the otherwise pristine handrail.
Usually, repairing such damage involves stripping the entire rail down to bare wood and starting over. But if the finish is shellac, a natural, nontoxic coating commonly seen in houses of this vintage, stripping isn't necessary. That's because, unlike varnish or polyurethane, each new coat of shellac dissolves into the one before it, so you can blend new into old without too much fuss.
For this repair, we enlisted John Dee, a painting contractor who has worked on several This Old House television projects. Dee dabbed, brushed, and padded smooth the new coats of bourbon-colored shellac. "You can't rush this," he said. His patience was rewarded in a few hours as the spot literally vanished beneath his intense gaze. It's time well spent; his work could last another 90 years, barring any more leaks.
Dee tested the finish by dabbing an inconspicuous spot with denatured alcohol on a cotton swab; this makes shellac tacky in about 30 seconds. If the finish doesn't dissolve, it's probably varnish or polyurethane, which requires stripping.
Clean and Soften
Wipe the damaged section and surrounding area with naphtha to remove any dirt, oil, or polish that might interfere with adhesion. (Wear chemical-resistant gloves and ventilate the area well.) Next, soften the damaged finish by rubbing it with a cotton swab dipped in alcohol. Wait 30 seconds, then dab with a clean cotton cloth. Repeat until any areas of rough finish are gone.
Smooth the damaged section and feather its edges with 400-grit, stearated (nonloading) silicon carbide sandpaper. Don't sand too deeply, or you'll need to apply more coats of shellac.
Pour a small amount of liquid shellac into a plastic container. Brush it evenly onto the spot, recharging the bristles every three or four strokes. Shellac dries quickly; add alcohol to the container if it gets too thick. Wait an hour for the first coat to harden, then brush another coat over a slightly broader area. Repeat, waiting an hour between coats, until the new finish is level with the old.
Form a clean cloth into a smooth, fist-size ball. Wearing latex gloves, dip the cloth in the shellac, tap it against the palm of your gloved hand to remove any excess, then quickly dab on a thin layer with one or two short strokes, no more. Allow 10 to 15 minutes for the film to dry, then dip and dab again over a wider area. Repeat until the boundary between the repair and the old finish disappears.
After the shellac cures for about a week, use an extrafine Scotch-Brite pad to put a protective coat of a top-quality tinted furniture wax, such as Briwax, over the entire rail. Apply the wax with a circular motion, wait a few minutes for it to harden, then rub with a cloth to a glossy sheen.