Concrete has become a popular material for contemporary kitchen counters and floors. A mixture of cement, gravel and sand developed by the ancient Romans, it hardens to a rocklike, porous surface.

But if not protected, concrete, like stone, will absorb salts, water and oil stains.

Old-fashioned beeswax and elbow grease can help beautify and protect a patinaed concrete floor or countertop, giving it an attractive, albeit slippery sheen.

Two other, more effective types of sealers have been around for decades but are now improved with stronger resins. They are formulated to protect new stone, masonry and concrete surfaces from acidic citrus juices, wine or vinegar and even soap or salt stains.

The first is a topical urethane- or acrylic-based transparent finish that is applied like paint; the other is a penetrating sealer that sinks into the molecular structure of concrete or stone and bonds to it to invisibly ward off spills and stains as an umbrella does rain.

Newly cured concrete floors can be protected with a penetrating sealer that, when brushed or sprayed on liberally, will sink to about 1/8 inch below the surface before it crystallizes and fuses to a slab of stone or concrete. This invisible water barrier will allow the material to breathe.

Concrete continues to cure and harden for decades. So a freshly poured floor shouldn't be sealed under a thick film of polyurethane that locks out stains and air because it will also lock in moisture and promote mold.

In certain instances, such as shower floors and kitchen counters, penetrating sealers chemically formulated with silane, a silicone-based molecule, to block oil as well as water are recommended.

Wait about a month before applying a sealer to a new floor, says Terry Tomlinson, a spokesman for Prosoco, a Kansas company specializing in stone and concrete sealers.

Concrete's alkaline corrosiveness, which diminishes as it dries, decomposes sealers if they're applied too soon.

Then keep the floor clean -- even protected concrete surfaces need care. ''If you don't wipe off spills, they soak in deeper,'' Tomlinson says.

Oil and water repellents generally incorporate Teflon -- ideally 3 to 4 percent -- in their formula.

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