Schluter Kerdi is a thin waterprrof membrane that feels like a thick paper with a fleece side that gets embedded in mortar and what must be a polymer infused side that is waterproof. The directions say to make the mortar thinner than usual but still able to hold a notch. I had pretty soupy mortar but it did hold a light ridge when spread.
Soupy mortar mix
On day one I had enough mortar for two shower walls. The shower is eight feet tall and will have a small ledge against the back where the insulation at the foundation wall is a bit wider than the outside 2 x 6 walls.
I cut full size sheets for the walls. Mortaring the bottom half first and installing the sheet and then holding that up with 2 x 4’s while I mortared the top half. That way the mortar did not get too dry for the membrane to hold.
Half wall with upper half mortared
I was supposed to use a 1/4″ notched trowel to spread the mortar but I have misplaced my tiling tools so I just used a new drywall paste spreader. It turned out the fleece absorbed the mortar with spaces between globs of mortar so it didn’t seem to be a problem. I smoothed out the membrane with the same rubber knife that I used to spread the epoxy bar coating on the cabinets. It really worked well to remove any bubbles under the membrane.
Membrane smoothed with rubber putty knife
I installed the rear wall first with the membrane centered on the wall. The membrane was unwieldy and it went on a bit crooked but not enough to worry about. I will draw level lines to lay the tile. I had to cut a longer piece to cover the ledges from the foundation insulation. It is all in one piece though so no need to overlap.
Rear wall installed
The membrane was installed right over the two wall niches. Later it was cut away to the edges of the niches.
Membrane over niche openings
Day two had the plumbing wall piece installed. The sides of the shower were narrow enough that the membrane was able to tuck into the corners and overlap the back wall membrane by the required two inches. Once the walls were covered and the niches trimmed with a razor knife, it was time to install the plumbing gaskets. The 3/4″ pipe gasket fit perfectly but the gasket for the shower control was too large for the valve opening so the alternative was to cut an extra piece of membrane with a hole to cover the piping. Later it will be caulked with the special Schluter caulk.
 Membrane shower pipe gasket |
 Handmade shower control gasket |
The Kerdi in the shower went in over Denshield fiberglass drywall although the specifications say that regular drywall can be used the paperless drywall is required by LEED. The space between the sheets were not taped and some of the screws were a bit crooked but the mortar covered these imperfections and the sides of the shower are very smooth and should be easier to tile than cement board with treated seams.
Membrane finished
I played around the plan for the tile layout. I’m used tan 6 x 6 tiles for trim on each end of the shower and they will go around the niches to make a finished edge. The bottom of the niches will be the dark brown trim tiles and I think the rear of the niches will be the wood round tiles. The floor will be the wood rounds and I would like to tile a strip of them up the plumbing wall. My niece says it is called a waterfall design. The rest will be the dark brown tile and the ledge is cut from the leftover family room bathroom granite.