Is it ok to use a Mastic for a repair rather than thin-set mortar that was used for the original installation?


Very recently I had my bathroom floor retiled. 6 x 24 plank style porcelain. The tile installer somehow chipped the corner of one of the tiles and had to come back and remove the tile and replace it with another one. When replacing it, he used mastic instead of thin set. He used thinset on the rest of the floor. Before he laid the tile he actually spread thin set over the floor to make sure it was completely level.

The tile that was replaced using mastic is now loose and when I step on it it’s moving, resulting in a grating noise and the grout is crumbling out. The installer tells me it’s perfectly fine to set tile with mastic, but I have read that the choice for floors should not be mastic but thinset instead.

The bathroom is not really used except for the toilet bowl so no showering has taken place in there. Another bathroom is used on a daily basis. Is this installer correct in saying it was fine to use mastic to set that floor tile? Thank you.


ANSWER - If the original tile installation was installed with a particular Thin-set mortar, then the repair should have been made with the same mortar or a rapid version of the same thin-set mortar.

Mastic is not considered the best product for installing tile on floors.  There are some mastics rated for residential light duty floors, but it isn't the best choice for a porcelain tile.

The only reason I can see that the installer would use a mastic rather than a thin-set mortar is because he didn't want to take the time and effort to mix the thin-set up in a bucket, and maybe he was able to avoid removing the existing thin-set from where the tile had been installed by using the mastic?

If the tile is loose, making noise, and the grout is crumbling out, then the tile installer should replace the tile and install it with the appropriate thin-set mortar.

2 thoughts on “Is it ok to use a Mastic for a repair rather than thin-set mortar that was used for the original installation?

  1. John Brandle says:

    If the tile came loose, why would it be a good idea to use the same thin set? Obviously it isn’t up to par. You should use something that you know will do the job, not match to something that didn’t work. If you’re worried about having more problems down the line, use a large format tile adhesive, or a premium thinset. And grout accordingly.

    • Donato Pompo says:

      It is very rare for an adhesive to be defective. When there are bonding problems most of the time it is due to installer error due to improper mixing or improper applying of the thin-set mortar, or going over a contaminated substrate or installing under extreme weather conditions without having proper temperature management controls that can lead to the thin-set skimming over.

      Most of the time when there is a tile bonding problem the thin-set bonds well to either the tile or the substrate and not to the reverse. As the thin-set manufacturers say “we don’t make one-sided thin-set. If it bonds on one side and not on the other, it isn’t the thin-set.”

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