Cut new control joints into existing concrete patios that are in good condition but do not have enough control joints. Control joints allow inevitable cracking to occur in locations that don’t weaken the concrete or detract from its appearance. They should be cut every 5 or 6 ft. in a patio. Plan the control joints so they will be below tile joints once the tile layout is established (photo, above right). Use a circular saw with a masonry blade set to %" depth to cut control joints. Cover the saw base with duct tape to prevent it from being scratched.
To establish a layout for tile with a modular pattern, you must carefully determine the location of the first tile. On the clean and dry concrete surface, measure and mark a center line down the center of the slab. Test-fit tiles along the line—because of the modular pattern used here, the tiles are staggered. Mark the edge of a tile nearest the center of the pad, and then create a second line perpendicular to the first and test-fit tiles along this line.
Make adjustments as needed so the modular pattern breaks evenly over the patio surface, and it is symmetrical from side to side. You may need to adjust the position of one or both lines. The intersection of the lines is where your tile installation will begin. Outline the position of each group of tiles on the slab.
Variation: To establish a traditional grid pattern, test-fit rows of tiles so they run in each direction, intersecting at the center of the patio. Adjust the layout to minimize tile cutting at the sides and ends, and then mark the final layout and snap chalk lines across the patio to create four quadrants. As you lay tile, work along the chalk lines and in one quadrant at a time.
Following manufacturer’s instructions, mix enough thinset mortar to work for about 2 hours (start with 4 to 5" deep in a 5-gallon bucket). At the intersection of the two layout lines, use a notched-edge trowel to spread thinset mortar over an area large enough to accommodate the layout of the first modular group of tiles. Hold the trowel at a 45° angle to rake the mortar to a consistent depth.
Set the first tile, twisting it slightly as you push it into the mortar. Align it with both adjusted layout lines, and then place a padded 2×4 over the center of the tile and give it a light rap with a hammer to set the tile.
Position the second tile adjacent to the first with a slight gap between them. Place spacers on end in the joint near each corner and push the second tile against the spacers. Make certain the first tile remains aligned with the layout lines. Set the padded 2×4 across both tiles and tap to set. Use a damp cloth to remove any mortar that squeezes out of the joint or gets on tile surfaces. Joints must be at least 1/s"-deep to hold grout.
Lay the remaining tiles of the first modular unit using spacers. Using the trowel, scrape the excess mortar from the concrete pad in areas you will not yet be working to prevent it from hardening and interfering with tile installation.
With the first modular unit set, continue laying tile following the pattern established. You can use the chalk lines for general reference, but they will not be necessary as layout lines. To prevent squeeze-out between tiles, scrape a heavy accumulation of mortar V" away from the edge of a set tile before setting the adjacent tile.
To make convex (above left) or concave (above right) curves, mark the profile of the curve on the tile, and then use a wet saw to make parallel straight cuts, each time cutting as close to the marked line as possible. Use a tile nippers to break off small portions of tabs, gradually working down to the curve profile. Finally, use an angle grinder to smooth off the sharp edges of the tabs. Make sure to wear a particle mask when using the tile saw and wear sturdy gloves when using the nippers.
After installing the tile, remove all the spacers, cover the tiled area with plastic, and let the thinset mortar cure according to the manufacturer’s instructions. When tile has fully set, remove the plastic and mix grout using a grout additive instead of water. Grout additive is especially important in outdoor applications because it creates joints that are more resilient in changing temperatures.
Use a grout float to spread grout over an area that is roughly 10 sq. ft. Push down with the face of the float to force grout into the joints, and then hold the float edge at a 45° angle to the tile surfaces and scrape off the excess grout.
Once you’ve grouted this area, wipe off the grout residue using a damp sponge. Wipe with a light, circular motion—you want to clean tile surfaces but not pull grout out of the joints. Don’t try to get the tile perfectly clean the first time. Wipe the area several times, rinsing out the sponge frequently.
Once the grout has begun to set (usually about 1 hour, depending on temperature and humidity), clean the tile surfaces again. You want to thoroughly clean grout residue from tile surfaces because it is difficult to remove once it has hardened. Buff off a light film left after final cleaning with a cloth.
Some tiles, such as slate, have highly porous surfaces that can be badly stained by grout. For these tiles, apply grout by filling an empty caulk tube (available at tile stores and some building centers) with grout and apply the grout to the joints with a caulk gun. Cut the tip to make an opening just large enough to allow grout to be forced out. Run the tip down the joint between tiles as you squeeze out the grout. Remove the grout that gets on the tile surface with a wet sponge. You may need to use your finger to force grout into the joint—protect your skin by wearing a rubber glove.
Cover the patio slab with plastic and let the grout cure according to manufacturer’s instructions. Once the grout has cured, use a foam brush to apply grout sealer to only the grout, wiping any spillover off of tile surfaces.
Apply tile sealer to the entire surface, using a paint roller. Cover the patio with plastic and allow the sealer to dry completely before exposing the patio to weather or traffic.