Sealer: what it does and what it doesn't

A spill left long enough can still stain sealed stone. Sealer doesn't stop acid from etching marble, and it doesn't make any stone scratch-proof or heat-proof, so keep using cutting boards and trivets. It won't repair an existing stain or dull spot. Quartz and porcelain don't need sealing at all, and on quartz, unnecessary sealer can leave an uneven-looking surface.

Test rather than follow a fixed calendar. On a clean, dry spot in an area you use, put a few drops of water and let them sit for several minutes, then wipe them away. If the stone stayed the same color, the sealer is still working. If it darkened, the water absorbed, and it's time to reseal. Never test with lemon juice or vinegar.

Depending on the stone and the product, resealing can be months or years apart. Let the stone dry fully, follow the sealer's instructions, and wipe off the excess as directed; leftover sealer can turn dense granite cloudy. For kitchen counters, choose a sealer suitable for food-prep surfaces. If you don't know what was used before, find out before adding more.