Step 1: Bleach Mildew Stains
Stir a teaspoon of powdered oxygen bleach (sodium percarbonate) into a cup of hot water until it dissolves. Wearing a nitrile glove, dip a stiff, nylon-bristle scrub brush into the solution and scrub the wood for a couple of minutes. Redip as needed to keep the surface wet. The mix will foam slightly, then subside.
Wait 10 minutes for the bleach to work, then rinse thoroughly with a sponge and cool water. The wood will lighten as it dries, but if it’s still stained, mix up a new batch of bleach and repeat the scrubbing process.
Step 2: Sand Burn Marks, Knife Cuts
Use a coarse, 60-grit sandpaper or sanding sponge to abrade the discolored wood, but don’t try to get rid of it entirely: Sanding too much in one spot will create a dip. It’s okay to sand across the grain initially, but be sure your final strokes follow the grain.
Step 3: Dissolve Wine Stains
Pour fresh hydrogen peroxide (3 percent solution) into a bowl. Use a cotton swab to dab the peroxide only on the stain; it can lighten unstained wood. Let the solution sit for a couple of minutes, then wipe with a damp microfiber cloth. Repeat until the stain disappears, or nearly so. Let it dry.
Step 4: Sand
Once the countertop is dry and the blemishes are mostly gone, sand the entire surface. Start with 100-grit paper, which should eliminate any remaining marks, then finish with 150. The best tool for this purpose is a 6-inch random-orbit sander, guided in slow, overlapping passes going with the wood grain.
Step 5: Fill Cracks
Melt canning wax in a small saucepan, then carefully pour the liquid into any cracks or separations. When the wax has solidified but is still soft, scrape off the excess with a 5-in-1 tool.
Step 6: Seal
Pour a wax-and-oil finish, like Butcher Block Conditioner, onto the wood and rub it back and forth with a lint-free cloth. Wait 20 minutes, then buff with a clean cotton cloth. To maintain the countertop’s stain resistance, reapply whenever the wood looks dry.
Step 7: Safe Finishes
In hardworking kitchens, food-safe oils and waxes are ideal finishes for butcher block because they’re easy to wipe on, and, for the most part, there’s no wait for them to cure. Mineral oil is cheap and readily available, but doesn’t last long. Blends of beeswax and mineral oil, like Howard's Butcher Block Conditioner, have a lovely scent, a bit of sheen, and better water repellency than mineral oil alone.
Steer clear of linseed oil and cooking oils, like olive and canola, which turn rancid. Also, avoid finishes like varnish and polyurethane; their hard films are difficult to refinish when they chip, peel, or get scratched.