Protect Your Investment: Stone Countertops

A quick scan of the real-estate listings will tell you the role stone countertops can play in marketing a home. "Beautiful luxury home with granite countertops," read a recent listing in Maryland. "Updated kitchen with marble countertops," related another from Seattle.

Part of the appeal of stone countertops is their permanence. But invincible they're not, even with the protective sealer that many stone countertops receive before, during, or after installation. To maintain the appearance and value of your counters, follow this advice:

• Know your stone. Natural stone falls into two main categories, according to the Marble Institute of America. Siliceous stone is composed mainly of quartzlike particles, and includes materials like granite, slate, sandstone, and quartzite. Calcareous stone is composed mainly of calcium carbonate, and includes marble (shown), travertine, limestone, and onyx. These stones are more sensitive to acid than siliceous ones.

Being able to identify what material your stone countertop is made of will help you care for it properly. To determine the type, apply a drop of distilled white vinegar to a discrete corner of the counter. If it starts to fizzle, the stone is calcareous; if it doesn't, the counter is siliceous. (If the counter has been polished or sealed, this test might prove inconclusive. )

• Avoid direct contact. Stone is very durable, but some materials, like limestone, are relatively soft and easy to slice, nick, and scratch, while others, like marble, get discolored more easily. That's why it's generally a good idea to use coasters under glasses, especially those containing alcohol or citrus juice; the acid from these liquids will etch or dull many stone surfaces. Also, avoid placing cookware you've just taken out off the oven or off the cooktop directly on your countertops; use trivets instead. And minimize scratching by putting dishes and flatware on place mats.

• Act quickly. Wipe up spills immediately with a wet towel or sponge, especially heavy-staining liquids like red wine. In our tests, stains that were allowed to dry overnight proved problematic for glossy and honed stones alike. If the mess is sticky or otherwise stubborn, use a dishwashing liquid and warm water. But avoid cleaning products that contain lemon, vinegar, or other acids, especially if your countertops are calcareous. Rinse the surface thoroughly after cleaning and dry with a soft cloth. Never use scouring powders or creams to clean spills—the abrasives can scratch the surface.

• Treat discolorations wisely. You can remove some surface discolorations with a mild detergent or an appropriate stone cleaner, available at hardware stores, home centers, and stone suppliers. You might need to treat deeper-set stains with a poultice, a pastelike material that you spread over a stain and leave there for over 24 hours. As the poultice dries, it wicks the stain up from the countertop.

• Reseal when appropriate. Even factory-applied sealers wear out eventually. If liquids are migrating into your stone surface, you might needs to reseal it. To test absorption, put a tablespoon of water right on the countertop; if the stone starts to darken after a couple of minutes, it is absorptive and would benefit from resealing.

Impregnator, or penetrating, sealers seep into the countertop, creating an invisible barrier beneath the surface. They are more common than topical sealers, which leave a visible film that might turn yellow under UV light. Penetrating sealers last for several years, whereas topical ones might need to be applied more frequently. Regardless of which sealer you use, make sure it's approved for food-handling areas and if you're applying it to kitchen countertops.—Daniel DiClerico

Essential information: Before you decide on a new counter, read our guide to countertops and refer to the Ratings (available to subscribers), which evaluate materials by how well they resist stains, among other performance characteristics.

Photo courtesy of the Marble Institute of America