What caused our tiles to Tent and become Hollow Sounding?

QUESTION

Hello! Any advice you have would be greatly appreciated. We built our home 8 years ago. Last year we had several tiles tent in our kitchen. We had the tiles replaced with our leftover tile by the company that installed it. When the tiles were lifted, most came out in-tact and clean of thin-set on the bottom of the tiles. There was thin-set noted on the concrete floor which proved very difficult for the tile professionals to remove. They were able to replace the tile. No foundation cracks were found and no water damage was present. Almost a year later, we just had this occur in a different area in our kitchen. At least 8-10 tiles are affected. The grout is crumbling, the tiles tented/have fallen back down and bounce when you walk on them. We have also noted several hollow tiles throughout our home. There is no pattern to this, some stand alone, some are in a cluster. The hollowed tiles occur in all rooms with tile. (master bath, kitchen, fireplace, and guest bath). All other floors (hardwood and carpet) have had no issues. We have counted at least 85 hollow tiles. Any thoughts? Thank you in advance!

ANSWER

ANSWER -  When tiles tent/buckle up it is normally due to the combination of lack of resilient movement joints and due to the tile not being bonded as well as it should.

Movement joints are grout joints that are filled with an ASTM C920 resilient sealant (caulking) so that they will diminish the stress in the tile installation that will naturally occur due to thermal expansion and contraction within the tile and moisture movement from the tile absorbing moisture.  The standards state that all perimeters and transitions within the tile installation should have movement joints, and any span longer than 24' for interior areas should have a movement joint; unless the interior area is near windows or skylights then the span should not be less than every 12 feet.

Because the hollow sounding tile was easy to remove and the thin-set adhesive didn't bond to the back of the tile, and because the grout was cracked around the hollow sounding tile, more than likely the tile was loose and was not bonded well.  Perhaps the installer spread his thin-set too far in advance and it skimmed over and it didn't bond well.  Or maybe the back of the tile had a contaminate on it.

Although hollow tile in itself is not a defect as the hollow sound can be caused by different conditions, it can be a symptom of a problem.  Chances are the tile wasn't bonded well enough and then the lack of movement joints caused the tile to be subjected to more stress than the tile could withstand, so that stress caused the tile to loose bond and the loose tile caused the grout to crack.

That is only a guess.  A forensic inspection with testing would have to be performed to verify what caused the failure.

There isn't much you can do to remediate your problem, other than replace the those tiles and install them properly.

2 thoughts on “What caused our tiles to Tent and become Hollow Sounding?

  1. Laura Sheets says:

    Hello, I hope this is the correct way to post my concern. Several tiles in my kitchen are tenting. The grout is cracked and I believe that if removed, the tiles could be lifted. I’ve researched possible reasons, and believe that a major contributing factor is the lack of a soft perimeter joint. The townhouse was built in 1987 and it appears that the 18 inch ceramic tiles were grouted without expansion joints or a soft perimeter. The tiles are in good condition throughout the house. ( One tile near the stove has a hairline crack.)

    We are currently renting but would like to purchase the townhouse, and I am worried that the floor could become a big problem. So I have three main questions:

    1. How would you fix (permanently or temporarily) the current tenting. (2 tiles tented, 2 other seem loose). I’ve seen products that recommend drilling through the grout and injecting more adhesive. Or removing grout, reattaching tile and regrouting.

    2. Can a perimeter expansion seam be added 30 years after the fact? Would it help to drill out the perimeter caulk and replace it with silicone? Would it be a good idea to replace the doorway grout line with silicone.

    3. Lastly, the current owners “updated” the bathroom by removing the old bathroom vanity and installing a free standing vanity. The tile stops where the original vanity sat, and there is a gap about 2×4 feet where there is bare concrete. Should this be tiled? Sealed?

    Thank you for any advice you are able to provide.

    • Donato Pompo says:

      Tiles that tent up have been subjected to more stress than they can resist from their attachment to the floor substrate. So there isn’t just one factor in what caused the tenting, but is normally due to several compounding factors.

      Lack of movement joints (expansion joints is only one type of a movement joint) at perimeters with constraining walls and maybe lack of movement joints. Movement joints are to be filled with an ASTM C920 sealant (caulking) which normally is a 100% silicone sealant or a polyurethane sealant. Or it can be just an empty joint at the perimeter that is covered with a top set base. You might need additional expansion joints throughout the installation every 20 to 25 feet in each direction or near windows with direct sunlight you need them every 8 to 12 feet in each direction.

      All tiles expand to some degree from moisture and from heat. They contract when they dry out or cool down. That is why we need resilient movement joints to mitigate that anticipate movements.

      Porous tiles absorb more and will expand and contract more than impervious tiles. So porous tiles have a greater propensity to expand.

      Depending on how well the tile is bonded to its substrate will depend on how resistant it can be to tiles expanding and contracting. When a tile tents it has gone through many cycles of expansion and contraction and at some point the stress may be greater than the resistance of the tile attachment. Tiles will weak attachments have a greater propensity to not be able to resist the tiles expansion and contraction stresses.

      If you treat the symptom of the problem, that doesn’t fix the problem and it will likely reoccur. If the tiles are butted up to walls you can cut out a 1/4″ gap. You can turn some cementitious grout joints into movement joints by removing the grout and properly installing the sealant. You can replace the tented tiles and maybe reinstall them if they were not damaged or install new tiles. There may be other tiles that have been compromised that need replacing.

      Whether you tile an open concrete surface is an aesthetics decision and does not have anything to do with how the floor functions.

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