Flooring Tile - Loose Tiles

:wall: I had finished grouting when I discovered a couple of loose tiles. I began checking all my tiles by knocking on them. I discovered that quite a few of my tiles made a hollow knocking sound in at least one of the corners. They don't seem to be flexing at all but I'm concerned that over time they will become loose and will need repair. Should I pull up the loose tile and relay them using a larger notched trowel? Could that fix my problem? I am working with 6 1/2" tile with 1/4" cement board over my existing lenoleum bathroom floor. I used a 5/32" V-notch trowel, which is what was recomended for the tile size. Could it be that the floor underneath the cement board is flexing and causing the grout lines to crack? How can I fix this? Do I need to install a thicker underlayment?

Both the linoleum and its related underlayment should have been removed before the tile was installed. It may well be that the floor is doomed from the beginning.

The size of the tile has almost nothing to do with the trowel that should be used, I don't know where people get off putting out information like that.

The back of the tile in conjunction with the type of subfloor in conjunction with the size of the tile is what determines which trowel should be used. Your trowel was too small.

On the first page one of the first two posts is written by D. Taylor, go read his offering and that will answer some of your questions.