Following the manufacturer’s instructions, apply adhesive to the concrete subfloor and lay down a crack-suppression membrane. Apply the adhesive in sections and unroll the membrane onto the floor, using a floor roller to press it flat and work out any air bubbles. Since concrete expands and contracts as the temperature changes, this membrane will help support the floor and prevent cracks in the tiles or grout.
Install the plastic grids that will hold the radiant-heat wires, using hot glue to adhere the grids to the subfloor. Follow the manufacturer’s instructions, and space the grids uniformly over the floor to prevent hot and cool patches.
Use a heavy-duty drill with a paddle bit to mix Thinset mortar according to the package instructions. Use a straight-edge trowel to apply a layer of mortar over the electrical cables. When mixed to the correct consistency, the mortar will stick and mound on the trowel without falling off. Make sure to hold the trowel at a consistent angle throughout the job so the mortar bed will have a uniform thickness. Allow the mortar to dry thoroughly before proceeding.
Mix enough mortar to work for 10 to 15 minutes at a time. If the batches of mortar are too large, it will start to dry out before it's applied to the floor.
Wet or cold weather will slow down the drying process, and below-freezing temperatures can keep the mortar from curing properly. Consult the manufacturer's instructions for guidance.
The best way to power the radiant-heat floor is to hire a licensed electrician to run a dedicated circuit from the home’s main electrical panel to the correct room. The electrician also can install the control panel/heating sensor in the wall.
Safety Alert: Always have a licensed electrician handle any electrical work that involves wiring a new circuit or working with the electrical panel or breaker box.
Dry-fit a vertical row of tiles and a horizontal row, leaving space for grout, to determine the best layout. The ideal layout will use as many full tiles as possible. The tiles against the wall should be a half-tile wide or wider.
Spread mortar on the floor, using the notched edge of the trowel to create deep grooves in the mortar. Press each tile into the mortar, wiggling it gently to seat it. Check the tiles for level and adjust as needed. Use tile spacers to keep an even grout line. Use a wet saw to cut tiles as needed for the perimeter of the floor.
Safety Alert: Always wear safety glasses and use caution when working with a wet saw.
After the mortar is dry, mix the tile grout according to the package instructions and apply with a grout float. Use a diagonal motion to apply the grout, working it into the spaces between the tiles. Let the grout dry slightly, then wipe the excess off the tiles with a damp sponge using a diagonal motion.
Let the grout dry completely before sealing. Once the grout sealant is dry, move the furniture back into the room. Let the mortar cure for four weeks before using the radiant-heat system.
Remember to remove the tile spacers before grouting.
The diagonal motion when applying grout works the grout in between the tiles. A straight vertical or horizontal stroke tends to dig the grout back out of the spaces.