Tom Boucher checks the shower wall framing for flatness with a six-foot level. Framing tolerances are important in a tiled bathroom, because tile joints will reveal any irregularities in the substrate.
Boucher cuts Kerdi-Board tile underlayment with a razor knife. The foam board is much easier to cut than traditional cement board, and pre-preinted lines at one-centimeter spacing make it simple to mark cut lines.
Boucher picks up a piece of Kerdi-Board after cutting it to size. The lightweight board reduces effort and fatigue for installers.
Placing the board against the wall and lifting it off the floor a few inches, Boucher marks stud locations on the board edge with a felt pen.
Special washers are used to screw boards securely to framing. Points in the washer pierce the foam's synthetic skin to hold the washer in place before the screw is driven.
Using pre-printed lines in the Kerdi-Board as a guide, Boucher positions his washers at one-foot spacing along the stud layout lines.
Boucher drives a screw through the washer and Kerdi-Board into the stud with a cordless impact driver.
Boucher mixes up a small batch of unmodified mortar, which he'll use to set Kerdi-Band polyethylene joint-sealing membrane over the seams in the Kerdi-Board.
Boucher applies mortar to the surface of the Kerdi-Board, working the mortar thoroughly into the substrate with the flat edge of the trowel in order to ensure a good bond.
Boucher uses a special Kerdi trowel with a one-eighth-inch square tooth to apply a measured amount of mortar to the joint.
Boucher presses the Kerdi-Band into the mortar with the flat edge of the trowel. When the ridges from the notched trowel are no longer visible through the translucent membrane, a good bond is assured.
Boucher likes to use a five-inch spackle knife, with the corners filed off to prevent gouging, to smooth down the Kerdi-Band membrane and remove excess mortar squeeze-out.
Pressing gently to avoid snagging the already placed horizontal Kerdi membrane, Boucher applies mortar to the wall corner and tools it with the short notched end of the Kerdi one-eighth-inch trowel.
Boucher uses the eighth-inch notched Kerdi trowel to control the amount of mortar at the screw location.