I have some tiles that make a knocking noise when walked on, the builder told me it was because water has gotten underneath the tiles and de-bounded them. The tiles are fixed to a concrete slab floor.

I didn't tile the floor, but from googling I think the styles have been put in place using a mortar bed. The trowel lines on the floor at from the previous tiles.

The water came from a dripping pipe, that was probably like that for 6 months.

Providing the leak is resolved, is there any way to fix this without ripping up the floor and re-tiling everything?

I have removed the poping tiles but the surrounding ones are wet, and there are big gaps under the tiles.

  • If it was just the cement damaged, then cleaning the old cement off the floor and tile and re cementing should work. I think the water has damaged the wood(by swelling) and pop off the tiles, this probably requires more intensive work, by replacing the wood. Tiles require very flat solid wood base to not crack.
    – crip659
    Nov 26, 2021 at 17:55
  • There is no wood involved here - the floor is concrete.
    – Dan
    Nov 26, 2021 at 18:21
  • Ceramic tiles installed on slab with thinset should not be subject to water damage. I think you need to investigate further what exactly happened. Where did water come from, where did it arrive and what exactly did it do to cause damage there? What was the component, the material, that was damaged by water, and how?
    – jay613
    Nov 26, 2021 at 19:04
  • In order to get a good answer you'd need to determine why the tiles are loose. If it was improper install or material then you probably should take up the floor. Did you use the recommended thinset and correct size trowel? Did you pull up tiles during install to ensure there was adequate coverage? Nov 26, 2021 at 19:32
  • Get the tiles up and use a dehumidifier to dry the concrete.
    – Solar Mike
    Nov 26, 2021 at 20:02

3 Answers 3


The Popping and the Water

Your two pictures, especially the second showing the bonding, and the your description about the knocking are revealing, and they are related.

The second picture shows large voids in the cement/thinset. Floor tiles must have more than 80%, preferably around 90% cement fill and bonding, where the voids are sporadic, small and isolated. Your pictures show much less total contact, and large contiguous voids.


It looks like the tiles were not set with a correct combing of the cement, and instead blobs and/or scrapes of cement were applied. This blobbing might have been an attempt to even the tile surface where the concrete floor dips, but it was not done correctly. To compensate for dips there should have been a base of self levelling cement applied first, or a different trowel used locally with coarser gaps for more cement deposit.

The main problem with large voids is poor support for the tile, leading to tiles cracking under heavy and hard drop loads (dropping pans, jars and bowling balls). Clearly this has not yet happened, even in a drop-prone area of the kitchen.


The popping sound effect has a different cause: the tile is not bonded to the cement, causing it to deflect and/or to teeter totter where there is even the slightest amount of play between tile and cement. The primary cause of this is poor bonding of the cement with the floor, or more likely, poor bonding with the tile. Thinset comes in different varieties, where some are suitable only for certain backings (concrete vs. plywood) and certain tiles (ceramic vs. porcelain).

Thinset for ceramic tiles cannot be used for porcelain tiles or even for some floor-rated ceramic tiles. This has to do with the amount of polymers in the cement and the porosity of the bottom of the tile. Dense and less porous tiles require a high polymere tile thinset cement, which is far more expensive (double-ish) than regular tile thinset. In an attempt to save cost perhaps a lower grade not suitable for the denser floor tile was used.

Even with the correct thinset, the unfinished concrete floor and the tile's back still require a wetting or keying of the surface, where the cement is worked in before it is troweled, on both surfaces. Omitting this step can cause poor bonding between cement and floor or tile. The ensuing micro-gap can give the tile just enough play to flex or teeter-totter resulting in the plopping sound.


The water ingress under the tiles is just a secondary symptom and not a cause: water permeates the grout or any pin-hole imperfections in it, through capillary effects and gravitation, and simply remains in the deep pockets under the tiles where it has little or no chance to evaporate.

The source of the water could be condensation on the tiles, water from mopping, spills etc...

Unless your kitchen experiences a freeze/thaw cycle (unlikely), the water is not the cause of the damage, but a result of poor installation.

The Solution

You can try to limit your fix to the problematic tiles only.

If the installation is poor enough, you might be able to carefully lift the tile with a crow bar or other flat lever. Work it by wiggling so that the tile does not flex excessively but so that the cement fatigues and releases its bond where it is still attached. Do this after scraping out the grout.

Then reinstall the tile with the correct thinset for the tile type, using the correct keying and troweling technique.

Where this fix is not possible, using epoxy grout can be used to stop the popping and water ingress. The tile will still lack proper support, but this does not have to be a problem since the tile has so far held up to the typical use and abuse in that area of the kitchen.

It is important to let as much epoxy grout as possible flow under the tile and provide some bearing to stop movement and not just side bonding. For this, as you scrape out the grout also try to scrape out a some cement under the tile, as an upside-down T, even if just a millimetre under the edge of the tile.

  • thats for taking the time to write such a comprehensive answer, very kind of you.
    – Dan
    Dec 4, 2021 at 15:39
  • @Dan no problem, and the new 2nd picture you uploaded confirms this. It seems that fortunately you can lift the tiles, and are they intact? Make sure to scrape out all the old cement. If you have a new question about keying or troweling, just ask on this site.
    – P2000
    Dec 4, 2021 at 21:21

I think if everything about the original installation was perfect, the tiles would not come up now. A little water would not cause this damage. Hard to say what was wrong. Maybe wrong thinset coverage, maybe it's not thinset but something else that is prone to water damage or that didn't stick to the concrete very well, maybe the slab had a non-porous coating on it, maybe other things. Doesn't really matter now.

In a high traffic area, on the floor, in the middle of the kitchen I'd say ripping it out is the "correct" approach. I would want desperately not to, and if the cabinets are sitting on the tile I'd probably try repairing to see how it goes. Either way I'd get someone with a LOT of experience to do this.

As a DIY-er I've made small tile repairs to obscure areas ... a corner of a backsplash, a closet floor, etc. I can do a pretty good job but it's never perfect. For this location I would want perfect, and I would want to know it will still be perfect for years and decades so I would hire someone with a lot of experience to do it.

Finally ... depending on the age of your house ... if this is the original floor in a subdivision, you might find out from neighbors with similar problems how they dealt with it.


Some people have had success using epoxy grout to fix tiles that have come de bonded.

When you say cement are you referring to the concrete slab or to the thinset used to bond the tiles? Both products contain cement. Generally cement based products aren't damaged by water.

Epoxy grout is expensive and hard to work with and you'd have to ungrout all around the tiles that are loose. You'd also either have to accept that the grout is going to be a different color or do a really good job matching the existing grout color.

Jeff Thorman has a good video on a tile that is flexing and how he epoxy grouts around the tile with good success. The epoxy grout is strong and bonds the loose tile to the surrounding tiles.


  • The thinset - I edited my question to clarify. If it's not damaged by water, do you have any idea why the tiles make knocking noises when I walk on them?
    – Dan
    Nov 26, 2021 at 18:19
  • @Dan What type of thinset was used? Mastic thinset is not water friendly. I get movement in my tiles because the thinset was not applied properly
    – rtaft
    Nov 26, 2021 at 19:05
  • 1
    The only way I can think tiles pop from water when they were bonded with thinset onto concrete is improper coverage. You can see in your picture the ridges from the notched trowel. When a tile is set properly the ridges are flattened. If the ridges aren't flattened you aren't getting full coverage ( there are different coverage requirements for different areas but generally you want full coverage especially for tiles that are being subjected to foot traffic ). Nov 26, 2021 at 20:37

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