How to fill a gap between counter and backsplash

April 13, 2011

Question: Every winter, the caulk in the 1/16-inch gap between my Silestone counter and backsplash dries up, allowing spills to reach the wall behind. The company that installed the counter didn’t mention that this would happen, so I was surprised. I’ve recaulked it twice with urethane acrylic sealant and adhesive, purchased from the installer. Can you recommend a more permanent fix? I have a lot of trouble getting the caulk into the crack and always make a huge mess.  ­­—Washington

Answer: You could switch to a silicone sealant, the lon­gest-lasting type, but there are several reasons to first give the urethane acrylic sealant and adhesive at least one more chance. Silicone caulk is a lot messier to work with, and though it grabs tenaciously to most surfaces, it’s virtually impossible to completely remove, and no other caulk will stick to the residue. So once you make the switch, you’ll never be able to go back to using a less messy product.

To get the best results from a fresh application of urethane acrylic caulk, it helps to understand that it is a water-based product that shrinks about 30 percent as it cures. The shrinkage makes up for the loss in volume as the water evaporates, so you cannot avoid it. However, you can cope with the shrinkage.

One way is to apply slightly more caulk than you want, so when it shrinks there is just the right amount. Then wrap the tip of a cloth around a finger and wipe the joint with that so you leave a rounded-in bead, suggests Michael Martin, technical director for Siroflex, which makes the Duo-Sil brand sold by some Silestone dealers. “If you make a real 90-degree corner, it’s too little,” he says.

But leaving more caulk than you want to see can be scary when you don’t do this task every day, because it’s hard to know what’s just right. The solution then is to clean up the joint so it looks right (even if that means a 90-degree corner), wait a week for that to cure, and then apply a second layer of caulk to fill in where the initial caulk shrank. You could never do that with silicone caulk, because it doesn’t stick well to itself; layers of urethane acrylic caulk do bond, though.

It’s very important to make sure the area behind the backsplash and countertop is completely dry before you apply the caulk. To ensure that, you may need to clean out the existing caulk and leave the joint open for several days before you reseal.

Question: I recently pulled up carpets in my house, exposing the wood floors underneath. Nails from the carpet strips left ugly black marks. These apparently go very deep and cannot be sanded out. I was told the only thing I could do is darken the floors, which I don’t want to do. Is there a way to get rid of these marks without changing the floor color? —Silver Spring

Answer: In theory, you could swab each hole with a deck brightener containing oxalic acid, which reverses stains left when tannin in wood interacts with iron in fasteners. But nails on carpet strips are often about four inches apart, so treating all of the holes would take hours. Also, you’d wind up with bleached wood around each hole. The cure would probably look worse than what you see now.

Instead, you might start by sanding a section and painting on a finish. Then stand back and decide whether it’s a look you can live with. Although the nail stains go too deep to sand out, the stains taper down, so even a relatively gentle sanding usually minimizes them enough so people don’t really notice them.

If the stains still bug you, consider drilling out the stained wood, using a bit with a diameter slightly larger than the stains. Then plug the holes with dowels of similar thickness or with wood filler.

You can also consider having a flooring installer replace the edge boards where the carpet’s tack strips ran parallel to the floorboards. This will leave only half of the holes to drill and plug.

Of course, you can also just leave the holes and consider them part of the patina of a house that’s been lived in over the years. People pay a lot of money these days for flooring made of recycled wood, which is often spattered with stains from nails and bolts.

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