The cement in grouting material is what makes it hard and takes a reasonable time to totally harden. If grout dries to fast the hardness can be reduced. To improve the resulting grout dampen (not soak) the joints between the tiles and hour or so before applying the grout. This can be done with a damp rag, brush, sponge, spray bottle etc.
Mixing the Grout:
When mixing dry powder grouts with water or a liquid grout additive, very little mixing is required to evenly blend the grout. Over mixing can entrap air bubbles which may increase shrinkage, allow moisture to dissipate easier and can affect the overall uniformity of colour. To reduce air bubbles add the liquid to the powder instead of the other way around. DO NOT MAKE THE MIX RUNNY! Mix to about the consistency of peanut butter. Let sit for about five minutes then lightly remix. The use of latex additive when mixing grout substantially improves the color and surface hardness.
Applying the Grout:
1. Apply the grout into the joints with a rubber-faced grouting trowel or float. To prevent internal voids pack the grout into the joints. After the joints are full, use the float to squeegee the excess grout off the surface of the tile and to level off the grout joints.
2. Let grout dry for about 15 minutes. Using a spray bottle spray a misting of water on the entire surface. Immediately use the float trowel and repeat the squeegee process to further remove surface grout and smooth out grout joints.
3. Let the grout sit about 30 minutes, then use a damp (not wet) sponge and lightly wipe surface of the tile. Do not use a circular motion with the sponge, use diagonal strokes so as to not disturb the grout lines.
4. Fine dust residue can easily be removed with a clean dry cloth the following day when the grout is hard and not subject to damage. Allow a minimum 12 hours to harden before further washing or in the case of the floors walking them.
5. All cement based grouts should be sealed to retain their appearance and reduce cleaning problems. Grout must be allowed to cure for a minimum of one week before applying a sealer.