"Tenting" tile and Moisture in a concrete slab [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-05-2007, 10:50 PM
I sure hope that someone can help with our problem and questions. We live in San Antonio and had ceramic tile installed on a concrete slab foundation (about 1300 square feet) about 5 years ago. Six months after the tile was installed, we had many tiles coming loose and I was able to vacuum the grout up from between the tiles. The flooring company that installed the tile came out and inspected the problem. They said we had "bad grout." They removed all of the grout (we lived in a dust storm for almost 3 days) and replaced approximately 60 loose tiles with new thinset and regrouted all the tiles. About 6 months ago, we had about 30 tiles that tented in one direction across one large room. We also had many (approximately 75-80) of the tiles coming loose again in various places and rooms. We removed the tiles that tented and checked under them to be sure we didn't have any cracks in our concrete slab. No cracks were found. Then last week we had another place where the tiles tented again--this time in another direction. We called the tile company and they came out again. They took one loose tile with them to inspect. (We haven't heard back from them yet.) They then sent out an installer who had a small handheld device that he said tested for moisture in the slab. He said our concrete slab registered "6" for moisture content and that was "not good." When we first bought the tile and had it installed, the salesman told us we couldn't put down vinyl or hardwood flooring because moisture would come up through the concrete slab and cause the vinly to mold underneath and the wood would warp. He said that ceramic tile would breathe and it was the best option for a concrete slab foundation. What may be the cause of the tiles tenting and the tiles coming loose in various rooms throughout the house? What are our options for repair? (I certainly hope we don't have to tear out all the tile and replace them.) I would appreciate any help or advice anyone may have to give us. (The tile installer said that our loose tiles may be caused by a cracked concrete slab, but we don't have any evidence of this.)

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03-05-2007, 10:57 PM
Welcome to the forum, JEK.

I think you may be with us for a while, so how about a first name we can call you?

The first thing I suspect is lack of expansion joints. Do you know if you have any? What about where the tile meets walls? Are they grouted right up against the walls, or is there a gap (could be caulked, and under some trim)?

Here's an excellent link from the reference libbery on expansion joints in case you need a primer on the subject...


03-05-2007, 11:05 PM
My Name is Janet. No, there are no expansion joints. I asked the tile company about that, and their reply was that expansion joints aren't necessary unless there is an expansion joint in the concrete slab-which there isn't. The grout goes right up against the baseboard, and we put shoe molding over the grout. I also asked about grouting right up against the baseboard and they said "That's how it is done."

03-05-2007, 11:09 PM
Hi Janet,

I'm sorry you're having such a problem with your tiles. I'm afraid your tile company is wrong on both counts. While they are correct that expansion joints in the floor must be brought up through the tile, additional joints may also be necessary if the span of the tiling is long enough.

They're dead wrong about grouting up to the walls. That is likely the source of your problem here.

03-05-2007, 11:11 PM
Thanks for your help. I did print out the information on Expansion Joints, and it appears to me that grouting right up to the baseboards may be the problem.

03-05-2007, 11:15 PM
right on Dan :tup1: I agree! And Janet, if you have substantial moisture (which I don't know how they tested) they should have recommended something like ditra to eliminate that worry all together. Sounds like the real problem is no room to grow. :(

03-05-2007, 11:24 PM
The installer had a small handheld device that he placed on the floor and pushed down. When he pushed down on the device, it made contact with the concrete floor and the meter on the device registered a reading. I looked at the meter and it did register between 5 and 6. Six was the highest reading on the meter. I just don't know what this means in regards to tile not sticking to the concrete. What is ditra? Janet

03-05-2007, 11:35 PM
Ditra is a product made by Schluter. It is a subfloor/moisture barrier/crack isolation membrane and I find extremely well suited for concrete floors. It is orange and you can find it at HD in the flooring section. For info on the product go to schluter.com. There is probably some info on it in the liberry.

03-05-2007, 11:38 PM
Rik, Thanks for all the help you are giving me. I will look up Ditra at the web site. Janet

03-05-2007, 11:54 PM
One other thing to remember. If you end up having to replace the tile and decide to go with the ditra, you will still need to put in expansion joints and schluter has good solutions for that too. Good Luck

03-06-2007, 01:34 AM
I agree it'd be a movement issue that's the bulk of your problems.Like in any faliure there's usually a couple other oddball errors that contibute to the proverbial "straw breaking the Camel's back."

How well were the tiles bonded? was there thinset on the back of the tiles and on the floor? How long had the slab been allowed to cure before tile was laid? Many other considerations and questions to ask the next tile guys...I think Ditra would be my choice. Plenty of good reading here on where and how to locate movement/expansion joints. Might also pick up a copy of the TCNA (Tile Council of N.America Handbook). It's our Industry Bible and has detailed drawings of every imaginable tile config.

Sorry to hear of your problems...There are good tile people out there :tup2:

03-06-2007, 07:57 PM
Thanks so much for everyone's help and reponse to our tile problem. I really do appreciate the advice and information. We have contacted a foundation company and we are going to rule out any slab problems before we proceed with the tile issue. Thanks again. Janet in San Antonio