The pleasant feel of warm tile under your feet on a cold morning will start your day off right. Tile's ability to hold and radiate heat from underfloor heating efficiently provides the benefit of a beautiful floor and keeps electric costs down. Installing tile on a floor with underfloor heat is a do-it-yourself job well within the abilities of most handy homeowners; the most difficult part will be choosing the tile. Ceramic and natural stone tile work equally well with the heated floor.
Using a smooth-edge trowel, spread a layer of thinset mortar over the electric heating mat. Mix a latex additive into the mortar to give more flexibility during the heating and cooling of the underfloor heat. Allow the layer of mortar to dry overnight. The installer of the floor heating system may have already installed the mortar to cover the heating cables.
Find the centre of the room by measuring the length and width. Determine the centre of the length measurement and pop a chalk line; repeat for the width. The point where the chalk lines cross is the centre of the room. Use a smooth-edge trowel to spread tile mastic from the centre line working in sections. Spread an amount of mastic that you can cover with tile in 20 minutes.
Lay the tile into the mastic using the chalk lines to keep the rows straight. Place spacers between the tiles to allow space for the grout. Continue spreading mastic and placing the tile until all full tiles have been installed.
Use a wet saw or tile nippers to trim the partial tiles to size nearest the wall. Place the partial tiles into the mastic and allow the newly laid tile to dry overnight.
Remove the tile spacers, and use a grout trowel to spread grout into the spaces between the tiles. Mix latex additive into the grout; this helps prevent grout cracking from the slight expansion and contraction of the heated floor. Wipe grout off the face of the tiles with a damp sponge; avoid overwetting the grout. Wipe any grout haze from the face of the tile with a clean towel. Allow the grout to dry overnight.
Use a smooth-edge trowel when working with heated floors. Notched trowels could nick the electrical cables.
Allow the recommended curing time for the tile before operating the underfloor heating.