Place the edge of a putty knife onto the grout between the tiles on your bathroom’s floor. Strike the handle of the putty knife with a hammer to break apart the grout until you can remove the tiles.
Pour a bag of thinset mortar into a bucket and then add the amount of water directed on the bag’s instructions. Stir the mortar mix and water with a drill with a paddle attachment until the mortar has the same consistency throughout.
Coat the floor with the new mortar, spreading the mortar evenly over the floor with a trowel until it is smooth. Spread the tile adhesive on the ridged side of the trowel, and then run the ridged side of the trowel over the mortar to create furrows in a single direction in the mortar.
Drop the new tile onto the mortar, placing plastic spacers between the tiles to keep the spacing even. Measure any obstructions such as walls or the bathtub and cut the tiles to fit using a tile saw. Remove the plastic spacers, place a board over each tile and tap it with a rubber mallet to seat the tiles in the mortar.
Press grout into the spaces between the tiles with a rubber float. Hold the rubber float at an angle and run it across the tiles to scrape away any grout that sits above the tops of the tiles. Wet a sponge in a bucket of water and then wring the sponge out. Rub down the tiles with the sponge, removing any grout film.