DEAR TIM: Pieces of granite tile countertop edge at my kitchen sink have fallen off. None of the pieces of granite have been damaged or cracked. I need a simple fix to reinstall the tiles. Is there a way to do this so the tiles will stay attached to the wood substrate for years and years? I’m worried about water leaking around the sink edge and causing the wood top to warp and rot causing even more problems. How would you repair this? What would you have done in the first place to ensure the granite pieces would have never fallen off in the first place? Roger C., Seattle, WA
DEAR ROGER: What a shame that you’re having this problem. The good news is the excellent photo you sent tells me everything I need to know to help you do a complete repair in less than 72 hours. I suggest that we get started fixing the countertop and then we’ll discuss how I would have done the job in the first place.
Your photo shows that the wood substrate is in excellent shape. There’s no residual adhesive and the wood appears to be sound. You’re lucky as it could have been much worse. To get a professional result, the substrate needs to be smooth, sound and in the same plane. That’s what I’m seeing now in your photograph.
If there’s any adhesive on the back of the granite pieces, it needs to be removed. I have no clue what it might be but I think I do see some cement-based thinset under one of the countertop pieces that’s still in place under the corner of your sink. You’ll need to grind as much of this thinset off the granite pieces as possible without damaging the granite. You may find a belt sander with coarse paper might do the trick.
Once you have the back of the granite cleaned up it’s time to concentrate on the wood substrate. It needs to be sealed so water can’t soak into the wood causing it to swell and rot. I’d use a clear water-based urethane for this job. It dries in an hour and you’ll need no less than two coats.
I’d apply one coat and then get busy fabricating a support frame that the vertical pieces of granite will rest on after they’ve been attached to the front of the wood substrate. Gravity will tug at the granite pieces causing them to slip and fall no matter what adhesive you choose to use. The frame with a tiny shelf prevents this movement.
Be sure the support shelf you construct is solid and will not move for at least 36 hours after you start to re-attach the granite to the front of the sink area. If I was there my frame would rest on the floor and I’d use blue painters tape to hold the frame to the front of the cabinets.
Before you mix up any thinset to reattach the tile pieces be sure that when the granite pieces rest on the temporary shelf they are flush with the top of the wood substrate. If you have to put thin shims under the pieces of granite to achieve this, that’s fine.
Apply one last coat of clear urethane to the wood substrate and as soon as it gets tacky mix up a small batch of Portland cement-based thinset. This is a great adhesive and it will bond well to the wood substrate. It’s best to apply it to the urethane just before it cures so you get a superior bond between the urethane molecules and the thinset crystals. The thinset should be the consistency of warm cake icing or a firm applesauce.
It’s very important that you apple the thinset to the back of the granite evenly and you press the pieces of granite to the wood substrate firmly. The face of the vertical granite pieces must be all in the same plane after they’re installed so the overlapping pieces of granite that slide under the lip of the sink are flush with the vertical face of the granite.
While this sounds hard to do, it’s not. You just have to have a nice metal 2-foot level that you can use to place across the face of the vertical granite as soon as you install them. If the wood substrate is smooth and you put on an even amount of thinset using a notched trowel, you’ll have no problems.
The flat pieces of granite that slide under the sink will not be too hard to install. It’s important that you get these in the same plane as the pieces of the granite tiles that are still in place at either side of the sink. Once again, use your 2-foot level, or a 4-foot one, to help you establish a line that’s in the same plane. Be sure no thinset oozes out that will interfere with the grout that needs to fill the spaces between each piece of granite.
Once the tile has set for 36 hours, you can grout the spaces between the granite tile. If you’ve never grouted before, use sanded grout and watch my four-part series on grouting ceramic tile on my AsktheBuilder.com website. Use my search engine to locate the video series. You can’t afford to make a mistake with the grout, especially in this wet location around a sink!
I feel the only mistake the original builder made in your kitchen was the failure to install a thin piece of cement board to the wood substrate. I would have done that because the thinset prefers to bond to the cement rather than directly to wood. If you do all I say above the thinset will bond permanently to the urethane-covered wood.
Once the grout has cured for about 36 hours, I’d apply a fine bead of clear caulk between the edge of the stainless steel sink and the granite tile that slides under the lip of the sink. Always be careful in the future and wipe up any water that collects here right away. You don’t want to take a chance that water gets under the lip of the sink.