Granite Sealers Should Run Deep

By Jeanne Huber
Special to The Washington Post
Thursday, September 7, 2006

Q My new granite bathroom countertops don't seem to be sealed. They change colors when water pools on them. How do I properly clean and seal them?

AYou're right in suspecting that the granite isn't sealed or is sealed only in some areas. Perhaps there was a sealer but cleaning solutions ate through it.

Whatever the cause, there's a simple remedy: Apply a penetrating sealer. It will sink into areas that are still absorbent and merely sit on the surface of any areas that were previously treated. As long as you wipe off any excess before it dries, you should be fine, says Scott Lardner, past president of the Marble Institute of America, a trade group that represents companies that work with many types of natural stone.

The main complication would come if the countertop were previously sealed with a non-penetrating finish. This type dries into a clear film that sits on the surface. Rarely used on countertops, it peels or turns white where water gets underneath. If you see evidence of this, strip the coating with a finish remover before you proceed.

Stone sealers come in water-based and solvent-based formulas. You'll probably want a water-based product. Clean the counter and let it dry before you apply the sealer. Directions typically say to use a brush, roller or sprayer, and they mean just that. "A lot of shops--we did it in ours, until I learned more--pour out some of the sealer and wipe it down with a paper towel," says Lardner, who is also president of Rocky Mountain Stone Co. in Albuquerque. "The sealer attaches to the most absorbent thing around. If you use a paper towel or a cloth, the active ingredients will attach to it and not to the stone."

Some of the material will work its way down into minute voids within the granite. The mineral structures in granite are impervious to moisture and don't stain, but the stone is still porous and susceptible to staining because of gaps such as hairline fissures in quartz crystals and seams between quartz, mica, feldspar and other minerals.

After about 15 minutes, wipe off the excess sealer. You can use a paper towel or a cloth for this step, because enough of the sealer will have penetrated into the stone by that time. Once you've sealed the stone, you should see water and oily spills bead up on the surface, at least for a while. But the stone may still stain if you wait all weekend to wipe up Friday night's corn-on-the-cob butter smears or red Kool-Aid puddles. Sealers buy you time; they don't stop the clock.

Maintain the sealer's effectiveness by cleaning the counter with mild soap and water, not a degreaser such as Formula 409 or an ammonia-based cleaner such as Windex. "These won't hurt the stone," Lardner says, "but they will degrade the sealer so you need to reapply it more often." Use only neutral cleaners on sealers; beware of even natural or homemade cleaners such as vinegar or lemon juice, which are acidic, or baking soda, which is alkaline.

When you put down a cold glass and notice a water ring on the counter or see dark spots where water drips off your hands near the faucet, it's time to reapply the sealer. Provided, that is, that you want your countertop to stay in like-new condition. "In the U.S., we want everything shiny and clean all the time," Lardner says. "We're the only country in the world that seals all the time. In Europe, they put in a granite countertop and if it gets dings and rings, no one cares."

My contractor used silicone to line the tiles at the bottom of my new shower. Black spots have appeared under the silicone and I can't clean them. Do I need to remove the silicone and replace it with grout, and, if so, how do I do that?

Unfortunately, you do need to remove the silicone, but you should replace it with new silicone caulk, not grout. The seam where tiled shower walls meet the floor is particularly prone to cracking because the walls and floor expand and contract in different directions. So you need to fill the seam with a flexible material, such as silicone caulk. Grout is too brittle.

The black spots probably occurred because moisture was trapped underneath the silicone before it was applied, according to Chris Turner, who answers technical questions at DAP, a caulk marketing company.

Spritz the seam with water and use a new razor blade to cut away the existing caulk. Scrape the seam as clean as possible. If any black spots remain, remove them with household bleach mixed half and half with water. Rinse off the bleach water. Then go over the seam area with rubbing or denatured alcohol, which will help to remove traces of soap scum. Let the area dry completely--maybe for 24 hours. Then apply new caulk.

Because silicone caulk was previously used in your shower, stick with that type for the next application. No matter how carefully you try to remove the old caulk, a thin silicone film is likely to remain. Fresh silicone will stick to that, while other caulk materials will not.

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