Over time, the decorative brick, tile, and stone used for the inverted U-shaped surround between the mantel and firebox are prone to soot buildup, staining, scratching, and pitting. Remove the buildup with a little know-how.
For soot, start with a neutral pH soap, like Ivory Liquid, mixed with warm water. (Avoid soaps with citrus or ammonia, which may etch surfaces). Use a stiff, natural-bristle (not wire!) brush to loosen grime. Repeat as necessary. Other suggestions that may work: scrubbing with an art gum eraser or applying Quick n Brite, a nontoxic, biodegradable cleaner.
Oily stains may come clean with a little paint thinner or mineral spirits.
Etched and pitted marble, slate, or granite can be touched up with wet-dry sandpaper, progressing from rough (80- to 120-grit) to fine (320 or better). Follow up with buffing powder, then a stone-specific polish.
For deeper stains on stone mantels, apply a poultice. On vertical surfaces, the easiest medium is a ¼"-thick layer of paper towels soaked in a stain-specific solution.
- For soot, mix 1-2 parts bleach to 10 parts water.
- For organic stains, mix 1 part hydrogen peroxide to 5 parts water.
Cover the paper towel poultice with plastic wrap and tape in place for up to 24 hours. With luck, the stain will lift out of the surface. (You may need to do this more than once.)