Schluter waterproofing has been our go-to product for almost every tile job for the last 10 years. The primary waterproofing product we use is the Kerdi membrane. It has a tough modified polyethylene core with non-woven polypropylene on both sides that bonds well to thinset mortar. The membrane is anchored to backerboard with thinset, and it provides a good foundation for thinset to hold the tile. Kerdi is lightweight, simple to install, and virtually idiot-proof.

We do all our own tile work in-house, and the only downside for us with the Kerdi product has occurred in situations that require multiple layers of the membrane. These can result in lumps, ridges, and generally uneven surfaces, over which setting tile is difficult. The place this occurs the most is in a shower niche or inset. With layers of Kerdi coming from top, bottom, and all sides, the inset can have multiple layers on multiple surfaces.

After working with the membrane for years, we developed a method that prevents lumps and unevenness by minimizing the number of layers and that uses only one piece of Kerdi. It’s a little like origami but isn’t too hard to execute once you see how it’s done.

One sheet of Kerdi. The author starts by drawing the back wall of the inset or niche on a piece of Kerdi. He expands that box to include the depth of the inset on all sides and then adds the prescribed 2 inches of overlap as the outside dimensions of the Kerdi paper. For this example, the interior box is 15 inches square; the second box is 23 inches square (2x4 wall with 1/2-inch drywall); and the sheet size is 27 inches square.
One sheet of Kerdi. The author starts by drawing the back wall of the inset or niche on a piece of Kerdi. He expands that box to include the depth of the inset on all sides and then adds the prescribed 2 inches of overlap as the outside dimensions of the Kerdi paper. For this example, the interior box is 15 inches square; the second box is 23 inches square (2x4 wall with 1/2-inch drywall); and the sheet size is 27 inches square.
With the perimeters defined, the author then draws a line from the corners of the interior box to the edges of the exterior box to represent either a cutting line or a folding line.
With the perimeters defined, the author then draws a line from the corners of the interior box to the edges of the exterior box to represent either a cutting line or a folding line.
Cut out. While Schluter doesn’t prescribe a specific way seams should lap, the author adheres to a shingling method to prevent potential water leaks. To achieve this, the top, or “ceiling,” of the inset is cut from the interior box outward, leaving flaps that will fold over the sides.
Cut out. While Schluter doesn’t prescribe a specific way seams should lap, the author adheres to a shingling method to prevent potential water leaks. To achieve this, the top, or “ceiling,” of the inset is cut from the interior box outward, leaving flaps that will fold over the sides.
Similarly, the sides are cut downward (toward the knees in this photo) to create flaps that will lap onto the base, or “floor,” of the inset.
Similarly, the sides are cut downward (toward the knees in this photo) to create flaps that will lap onto the base, or “floor,” of the inset.
The entire piece is folded and scored once; the creases provide some rigidity needed for the install.
The entire piece is folded and scored once; the creases provide some rigidity needed for the install.
We then apply thinset to the entire opening and are ready to install the precut, prefolded sheet.
We then apply thinset to the entire opening and are ready to install the precut, prefolded sheet.
Installation. Starting at the bottom, the author aligns the back corner and presses the membrane into the back wall and bottom of the inset. He adds thinset to the bottom corners so the side flaps will adhere over the base. The side walls may then be pushed into the thinset.
Installation. Starting at the bottom, the author aligns the back corner and presses the membrane into the back wall and bottom of the inset. He adds thinset to the bottom corners so the side flaps will adhere over the base. The side walls may then be pushed into the thinset.
After the side walls are secure, he adds more thinset to the top of the sides to adhere the top flaps onto the walls. He then presses the flaps and ceiling of the inset in place. All that remains is to spread thinset on the surface of the shower and press the 2-inch perimeter flaps into place.
After the side walls are secure, he adds more thinset to the top of the sides to adhere the top flaps onto the walls. He then presses the flaps and ceiling of the inset in place. All that remains is to spread thinset on the surface of the shower and press the 2-inch perimeter flaps into place.

All photos by Jake Bruton

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