Things You'll Need
Bucket of water
Ordinarily when you lay down tile, you have to mix up a batch of grout to press in between the seams in the tile. This provides added stability and waterproofing — once the grout is cured — to protect the material under the tiles. Premixed grout, as you might have guessed, skips the entire "mixing" stage and allows you to apply grout to the tile as soon as the tile adhesive dries.
Clean your tiles with a damp sponge to remove any obvious dirt or grime, then rinse out your sponge and set it aside.
Open the premixed grout container and scoop a glob of it out onto the tile with a trowel.
Hold a grout float at a 45-degree angle and use it to push the grout into the seams between the tiles. Make sure to apply significant pressure as you work the float back and forth over the tiles. Use strokes perpendicular to the seams so your float doesn't dig out the grout.
Continue applying the premixed grout over the tiles until you have filled all the seams in the area where you are working.
Remove the excess grout, using a damp sponge. Remove the bulk of the grout with circular motions, and then make one last wipe parallel to the grout lines. Make sure you pause every now and again to rinse out the sponge in the bucket of water. Do one last wipe-down with a clean sponge over the grout lines once you have removed all the grout.
Continue applying grout and wiping it off until you have filled all the seams between the tiles.
Wait for the grout to dry, then return to the tiles and use clean rags to wipe down the film that appears on the tiles around the grout. You may need to dampen the rags in order to thoroughly clean off the film. Let the grout set for the manufacturer-recommended period of time.
Apply grout sealer to all the grout lines.
Some grouts may require you to wait 45 minutes or more between the time of application and when you clean off the grout for the first time. Make sure you consult the packaging or instructions before you start working with premixed grout to find out the exact times. Do this to find out the time necessary for the grout to dry before the second cleaning as well.