where to end uncoupling membrane on floor in relation to drywall?

Submitted by marshgirl12 t3_z8dr2w in DIY

Hi all- gearing up for a project in my basement where I will be adding tile overtop of a now concrete floor. I've done my research and landed on the uncoupling membrane as being what I think will work best for my house. I'm a bit confused as to where to end the uncoupling membrane. I know with some of the other floor underlayments people leave about a small gap on the floor before the drywall, however with uncoupling membrane it seems like people run it up the wall a few inches. There is a moisture vapor barrier between the insulation and drywall if that is useful information. Any help or resources appreciated. Thanks!

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5degreenegativerake t1_iyb5n5l wrote

End the uncoupling membrane even with the drywall. If you are expecting the floor to be regularly very wet, you can roll waterproof membrane up the drywall a bit and stop short enough for the base molding to cover it, or use tile base molding over the membrane to make it actually waterproof.

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marshgirl12 OP t1_iycjt32 wrote

Thanks! This is very helpful. Also where does the tile end then? Like where the uncoupling membrane ends?

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huskers2468 t1_iycv18r wrote

Smaller gap than your baseboards. Just think of trim as covering the gaps, so you can make a bit less accurate cuts, and move faster.

My biggest issue was that I kept making my cuts so tight I had to either fit them in place or recut. Instead, just give yourself another 1/8th of an inch and move on.

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Danny141035 t1_iyburcy wrote

UM should go tight within reason to the drywall 1/4”-1:8” gap. You would never run UM vertically. What your seeing vertically is a fleece lined waterproofing membrane. The 2 most common products for this are made by Schluter Ditra (UM) and kerdi (waterproof membrane) in a basement there is absolutely no need to use the fabric membrane on the wall, it’s mostly used in showers and bathroom floors. Be sure to honor the control joints cut into your concrete slab. Otherwise they will in time translate to the tile above and crack them. TCNA section EJ 171

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marshgirl12 OP t1_iycjrqf wrote

I’m not familiar with control joints, the concrete is also pretty old. Could you provide more guidance?

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Eyiolf_the_Foul t1_iyctr9o wrote

They are to control cracking in the slab as it cures-you may not have any in your basement. If the slab is in good shape just apply your membrane over the whole surface.

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bassboat1 t1_iydjla9 wrote

Control joints are cast-in-place (look down the next time you're on a sidewalk), or sawn after the concrete has hardened (often on a 10' or 12' grid). It's expected that a concrete slab will shrink as it cures and inevitably crack. The control joints will (hopefully) limit the cracking to the grid and not occur randomly, at angles, etc... Fiber additive or welded wire mesh is embedded in the concrete to help prevent the now separated pieces from moving vertically with respect to each other. The uncoupling membrane prevents the cracks from telegraphing through bonded materials like tile. On large slabs, expansion joints are required, and they should be continued up through the tile as a caulk joint.

Do not run Ditra or the fleece products like Redgard/Custom up the wall. Kerdi can be run up the wall in some shower systems.

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Beach_Mountain50 t1_iybauip wrote

You’ll want to double check if I am correct. Let’s say you use Schluter DITRA uncoupling membrane. I would have a 1/8 inch space between DITRA and the wall. Then I would crease a 5 inch Kerdi membrane in half and bond it to the DITRA and the wall with thin set.

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