Use Mapei grout by mixing it according to the instructions on each bag or bucket and using a grout float to place the mixture between tiles to seal out moisture. Mineral spirits can help prepare tiles for grout installation, and a cellulose sponge can simplify cleanup afterwards.
Prepare the tile area for the application of grout by removing any existing grout or spacers on a new tile installation. Mineral spirits help trap dust and contaminants that may negatively affect the quality of the grout. Mix dry Mapei grout with water according to the specifications listed on bags of the substance, or open the bucket of premixed grout.
Fill a grout float with the mixed solution, and use it to fill in the spaces between each tile in the installation. Ensure that the joints fill fully with grout, as spaces could lead to future contamination. Draw the float back over areas to ensure that grout remains flush with tiles and does not overlap them. The clean edge of the float can help remove excess grout from tile joints as needed. The grout requires time to set after installation, which may take 30 minutes or longer. Once the grout hardens completely, use a cellulose sponge to remove any remaining grout residue from the tiles.