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Unread 04-24-2021, 06:58 AM   #1
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Kerdi-Board Knee Wall

Using the Kerdi system to build a shower in our home (membrane over Fiberrock, band, drain, foam pan, bench and curb). Looking to add a knee wall and decided between building one out of 2x4s or out of 2” thick Kerdi-Board doubled up to 4”. I’ve watched it done on Schulter’s YouTube channel. They do it by using thin set or Kerdi-fix to bond the two pieces of board and then thin set or Kerdi-fix to bond the knee wall to the floor and existing wall. They insist the wall becomes more sturdy once tiled. But my concern is just using mortar, will the board be sturdy enough? Does anyone have experience using the Kerdi-Board to build a knee? Opinions on that over building it out of 2x4s, fiber rock, then Kerdi membrane? I guess my immediate concern would be matching the thickness of the 4.5” wide Kerdi curb being installed.
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Unread 04-24-2021, 08:13 AM   #2
Tool Guy - Kg
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Welcome to the forum, Brian.

The sturdiness of knee walls is in the little details of making each and every part tight, so that you have 'material-to-material' contact. You don't want to build a wood wall with slight gaps in the joinery and be fooled into thinking that screws will make up for the slightly sloppy joints. One advantage of building it with wood is that you've got the option of any wall thickness you want without purchasing additional thicknesses of KerdiBoard. Building it from KerdiBoard removes some of those details with the simplicity of it all (and don't forget that 2 layers of 2" KerdiBoard laminated is awfully stiff even without tile). I could go either way on construction, but if I were to make a wood stud wall, I might consider skinning the sides with plywood to further stiffen the joints so that the wall acted like a single, stiff box.

The biggest advice I can dispense without seeing your exact scenario is to pay attention to tight joinery. If you showed us a picture with details, we might offer specific advice applicable to your exact situation.

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Unread 04-24-2021, 10:26 AM   #3
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Schluter does sell U-channel to fit the 2" Kerdiboard panel edges that offer you the chance to anchor it to a wall or floor, and to help stiffen a long edge. Kerdiboard is flat, stable, and won't warp, easier to cut, and not damaged if it gets wet. Depending on the tools you have and how much you value your time, it may end up less expensive than building it out of wood and then covering it. WediBoard is some neat stuff, too. Trying to build something like this out of wood would be a major piece of engineering, time, and effort...
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