In the vast majority of cases, tile grout will be good, old Portland cement with no sand or other fillers. There is a technique to curing this tile grout. The trick lies in keeping the grout moist but not allowing water droplets to drop onto any part of it while it is curing. Water drops can cause different parts of the grout to cure at different rates, causing spots of discoloration and even weakened grout. Time and the right amount of moisture are the keys to proper curing and long-lasting grout.
Things You'll Need
Portland cement grout
40-weight "Kraft" paper
Grout sealer (aerosol)
Wipe newly grouted tiles with a damp (not wet) grout sponge, moving the sponge across the face of the tiles diagonally and exerting only minimal pressure. The idea is to level the grout with the surface of the tile and remove any excess grout from the face of each tile. The dampness of the sponge adds just a bit of moisture to the grout, which is important for the curing process.
Lay 40-weight Kraft paper on top of the damp grout and tape down the edges of the paper so that the paper will maintain the dampness of the grout, sort of like a paper greenhouse. It is vital that grout be damp-cured for optimum strength and long life.
Leave the paper over the curing tile for 72 hours. Do not walk on the tile or interfere with it in any other way during the 72-hour damp curing phase.
Remove the Kraft paper after 72 hours.
Apply grout sealer. Many grout sealers now come in aerosol cans and can be sprayed directly onto the grout with no need to wipe the face of the tiles clean. Follow the manufacturer's instructions when using an aerosol sealer. Paint on other types of sealer using a sponge paint brush, wiping any excess sealer off of the face of each tile as you go along.
When using epoxy or other types of grout, it is important to follow the manufacturer's instructions for curing, as each type of grout has slightly different curing instructions.
Kraft paper is available locally from tile shops and many home improvement centers, or can be purchased online.