I recently had a room tiled and during the installation I had noticed the workers were putting a small empty space in the mortar underneath some tiles. They wanted to adjust the alignment of the tiles so they removed the mortar separating them and then pushed them horizontally. They told me that this was not a problem and that the tiles should resist despite the small gap below.

The problem is that now I'm wondering whether what they said was true or not.

  • I'm not really following your question at all. Perhaps you might edit it and make your question more clear. – jwh20 May 29 '20 at 11:22
  • @jwh20 the mortar below the tiles was not full – R Rako May 29 '20 at 11:29

The way I read your question is that due to some misalignment in the tiles, they were removed and some of the mortar was removed and the tiles replaced with a gap underneath. If the gap was filled when the tiles were pushed horizontally, you'll be fine. If a sizable gap remained, you could have a problem with the tile cracking if you step on it just right, heel to tile. Once the mortar has dried knock on the tile and listen for a hollow sound, which would indicate an air gap. Make sure you keep a number of extra tiles incase you do develop a problem.

  • 1
    I agree with jack, once the tiles have a coating called back buttering , very thin and there is thinset on the floor they may have been leveling by removing a little bit, this would show they were paying attention to detail and an above average install, many do not back butter but it works the thin set into the tile better and provides a better bond than just pressing a tile into the thinset. – Ed Beal May 29 '20 at 14:45

Not only should you not be concerned about gaps in the mortar beneath your tiles, but you should be concerned if there are not gaps!

Mortar is applied to the substraight and to the back of the tile with a notched trowel.

The notches do two important things. First, they make it easy to apply only a specific amount of mortar. No matter how much mortar you pile onto the trowel, the notches apply it in nice, even lines of identical thickness. Second, the trowel creates spaces between the lines of mortar. These allow air to escape when the tile is pressed into the mortar. Without the spaces, you could get air pockets that prevent the tile from lying flat or adhering properly.
Source: The Spruce

If they were intentionally creating small hollows to hold air in (with a "dam" around it to ensure the air was trapped) that would be a different thing and may be questionable.

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