Installing the Curb for a Tile Shower

Tile contractor Tom Boucher with a two-inch-thick piece of Kerdi-Board. The board has an extruded polystyrene core and is faced with polyethylene membrane with a fleecy surface that is able to bond with mortar. Boucher has ripped the piece on a bevel, which will create a slope for drainage when the shower curb is topped with a piece of marble.

Boucher cuts two matching pieces of Kerdi-Board to length with a circular saw. The two pieces will be laminated face to face using cementitious mortar to create the shower curb.

Boucher works mortar into the faces of the Kerdi-Board pieces. Pressing the mortar into the Kerdi-Board is important for achieving a good bond. Once the mortar sets up and cures, separating the pieces will be virtually impossible.

With both matching Kerdi-Board faces pre-coated with mortar, Boucher adds more mortar to one of the faces and tools it to the proper depth using a special Kerdi trowel with one-eighth-inch notches.

Boucher lays the mortar-covered Kerdi-Board pieces together.

Boucher presses the two Kerdi-Board pieces together to create a good mortar bond at the lamination joint.

Boucher used unmodified mortar to join the two pieces of the curb together. Here, he mixes up a small batch of modified mortar, using latex additive, for adhering the curb to the engineered wood panel subflooring. Unmodified mortar is used whenever impervious layers are laminated together; modified mortar is used when the wet mortar will have the ability to dry by evaporation or absorption (in this example, over the Advantech subfloor).

Boucher applies mortar to the subfloor in preparation for installing the Kerdi-Board curb.

Boucher presses the laminated Kerdi-Board curb down into the mortar bed. Once the cement sets and cures, the curb will be solidly attached.

Boucher cuts Kerdi membrane to width before adhering it to the built-up curb. The membrane will be layered onto a mortar bed over the curb to create a waterproof substrate for tile.

Boucher applies mortar to the polyethylene face of the Kerdi-Board curb.

Boucher applies mortar to the inside face of the curb. As in every situation, the first step is to work the mortar thoroughly into the surface that's being prepared, to ensure a good bond.

Boucher applies mortar to the previously installed sloped shower base (the installation of the shower base and drain is not shown here, but is covered in a different slideshow).

Boucher tools one-eighth-inch grooves into the mortar bed using a special Kerdi trowel. Applying a consistent, uniform, measured amount of mortar to the substrate before installing the membrane is one of the keys to success for the system.

Boucher presses the membrane down into the mortar using a float, to create a firm, positive bond.

Boucher works the membrane into solid contact with the mortar using his six-inch spackle knife.

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