For grout joints wider than 1/16” you’ll want to use sanded grout. Having sand mixed into the grout gives the grout extra strength to keep it from cracking (the same way that gravel helps make concrete stronger). Most floor tile installations will use sanded grout.
For grout joints thinner than 1/16” (typically on walls and sometimes on countertops) non-sanded grout will work just fine. It’s also easier to work the creamy, non-sanded grout into smaller grout joints.
Picking the right color for your grout is one of the biggest challenges. The printed colors shown in grout brochures will be a little misleading. We almost always recommend buying a small quantity of several grouts and doing some real-life samples
For floor installations, some tile contractors we know will actually pour dry grout over small areas of the floor, sweep it off the surface and get a sense of how the different color grouts will look in the actual setting. (The advantage of this method is that they can then just vacuum the dry grout out once the decision has been made.)
But dry grout will not have the same color as the same grout once it’s been mixed, applied, finished and then left to cure. So when we’re in doubt about the color we take some leftover tile, glue it to a scrap piece of plywood, and actually mix up the grouts we’re considering, apply them, let them cure, and THEN make our choice.
Our other bit of advice about grout colors: don’t use white grout on a floor or countertop. It’s hard to keep clean. A light gray grout will keep up its appearance better.
Follow the directions of the bag or box for mixing the grout. Mix up only as much as you’ll be able to use in about 30 minutes.
Just like with thinset mortar, after you’ve mixed it well, let it “slake” for ten minutes or so to let the moisture penetrate any remaining globs of powder and to give any additives in the mortar time to activate. Then give it one last stir.
You’ll use a padded grout float to spread the grout over the tiles and force it into the joints. For wall applications you can usually scoop up the grout from the bucket with the short side of the float. For floors you’ll want to use your ever-present, handy-dandy margin trowel to scoop globs of mortar onto the floor.
We like to say that if you aren’t working up a sweat when you’re grouting then you’re not doing a good enough job. You drag the grout across the whole surface of the area with the long side of the float and then use two hands on the float to push it down into the joints.
When you’ve finished an area (we usually work in areas about 3’ wide and 2’ deep), hold the long edge of the float almost perpendicular to the floor and scrape the excess grout off the surface of the tiles. When you’re scraping the grout, make sure you’re sweeping diagonally to the joints so that the float is always running along the surface of the tiles and not accidentally digging the grout out of the joints.
When you’re working on a floor you usually just scrape the grout across into the next area you’re going to work on. When you’re working on a wall you’ll probably end up with the excess grout on the float. Either scrape it back into the bucket of grout or go ahead and spread it out in the next area you’re going to work on.
Cleaning Off Tile
You’ll have to use some judgment about how long to continue with the spread-smush-and-scrape phase before you go back to clean off the surface of the tiles. You want the grout in the joints to have a little time to harden, but you don’t want to wait so long that the residue on the surface of the tiles gets too hard to clean off. For a do-it-yourselfer, an area the size of the back wall of a bath/shower surround (or maybe about 10 square feet of floor) is about as much as you’ll want to do before starting to clean the tile surface.
You'll need a bucket of fairly clean water and a soft, thick sponge for cleaning off the grout. Use a gentle circular motion with a damp sponge to clean the surface, rinsing the sponge out often.
When you can’t see grout any more on the surface, move on to “shaping” the grout in the joints. Gently run a damp sponge parallel to the direction of the joints, trying to get the grout just a little below the surface of the tile. But try not to expose the edges of the tile. Here it's especially important to be using a fat sponge with big, rounded edges.
When all the joints look good, you’re ready for the final wash.
Squeeze the sponge out pretty dry and wipe it gently along the surface of the tile with one stroke. Flip the sponge over and use the clean side for the next stroke. Then rinse the sponge and repeat, working across the area. Resist the temptation to make more than one stroke with one side of the sponge. (Some pros use two sponges, one in each hand, to minimize the trips back to the bucket.)
The job will look great while the surface of the tiles is still wet. But as they dry off you’ll notice a slight haze forming. If you’ve done the washing right, this haze will be so thin that you can leave it on while the grout in the joints continues to harden. You should be able to come back a little later and use a soft rag to gently rub the haze away.