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Ask the Remodeler: Dealing with crumbling tile grout and shower walls

Mark Philben offers readers advice on grout and the proper tile underlayment. Get more expert tips on home repair at

Send your home repair questions to [email protected]. Adobe Stock

Q. More than 20 years ago, I had roughly 440 square feet of ceramic tile installed (in the kitchen, half bath, laundry room, and foyer). The work was done by a professional flooring guy. I have forced hot air heat/central air conditioning, and the ductwork for those living spaces runs just below the floors. Where the ducts are, I have to continually regrout between the tiles because it dries out and crumbles. I’ve tried just about every brand of grout but cannot find anything that will stand up to the heating and cooling. Is there a solution I can add to the grout?


R.O., Dracut

A. A couple of things may be happening here. Twenty years ago, not everyone was using cement board as a substrate. We see a lot of tile just bonded to the plywood, which is not a good substrate and causes a lot of movement and cracking. It’s hard to check for that, and there’s not much you can do to repair it without ripping up the floor.

But there may be a simpler solution: checking the insulation and air sealing on the ducts. A properly installed duct should lose essentially no heat or cold air. If the ducts are losing enough heat to cause movement in the floor, that can easily be corrected.

Finally, you can use an acrylic grout additive to make the grout more flexible or an epoxy grout for strength. It is hard to say which one would be more effective in your case, but one of them should help. Good luck!


Q. Our shower is crumbling! It’s a 3-by-5-foot walk-in with marble 12-by-12-inch tiles, and it has possible water damage under the tiles. The cost estimates to repair or replace it are astronomical. We need an experienced, knowledgeable general contractor who will be honest with us as to what is actually needed. Any assistance or advice would be greatly appreciated.



A. I am sorry to be the bearer of bad news, but it does sound as if you need more than a repair and probably to take at least the shower walls apart and start fresh. The shower floor may be OK because they would have most likely used a copper pan with a mortar base, and that may still be sound. It may be that you have the wrong backer board behind the tiles and that it is failing, taking the tiles with it. Most likely you will need to remove walls (and possibly the ceiling) down to the studs. Check for mold on any of the wood framing. If it is present, stop and call a mold abatement company to have it removed or treated.

Once the framing is ready, a proper backer board or cement board should be applied to the framing. This should overlap the pan used for the shower floor. This needs to be waterproofed with a field-applied, liquid-based sealant and allowed to cure. Once that is done, tiles can be installed, grouted, and sealed. I wish there were an easier solution, but it does sound as if you have fairly severe wall failure and that patches or repairs will only make things worse in the long run.


Mark Philben is the project development manager at Charlie Allen Renovations in Cambridge. Send your questions to [email protected]. Questions are subject to editing. Subscribe to the Globe’s free real estate newsletter — our weekly digest on buying, selling, and design — at Follow us on Facebook, Instagram, and Twitter @globehomes.


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