Fireplaces are often centerpieces of living rooms, providing both fashion and function. Generally, a mantel sits above the fireplace, allowing for decorations or familial items to be placed on them, such as framed photographs. If your house has a fireplace but is without a mantel, you can install one with time and effort. However, you'll need to use a sealer so the mantel, whether it is wood or stone, does not become heat stained. Applying sealer to a mantel is simple, and the positive effects last for years.   Clean the stone with a commercial formula developed for cleaning the porous surfaces of stone. Remove all residue according to the cleaning manufacturer's instructions. Allow the mantel to fully dry. Purchase a stone sealer from your hardware store, checking the fine print to see if it is suitable for heated areas. You can purchase the sealer so it is not visible on the mantel, or adds a darker or lighter tone, or adds gloss when it dries. Tile Guard Natural Stone Premium Sealer is a good sealer for almost any stone, but you should use a more solid sealer for porous sandstone. Use stone-enhancing sealers for mantels that require more depth and color.