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Waterproof Shower using Kerdi Membrane

Harry Dunbar's contact information
Barrie, Ontario, Canada
Phone: (705) 424-5144
Toll Free (Ontario only) 1-866-837-7773

How It Came Together.
By: Harry Dunbar

My customer had several panels of DensShield on site. I said I would use it, but that we still needed to install Kerdi waterproof membrane and drain system. The DensShield is a gypsum product and I refuse to use it, or any other gypsum product as a "Stand-Alone"waterproof system in any of the showers I build.
I've used a cement board (WonderBoard) for the exterior wall to the right. There is a vapour barrier already installed on that wall, so instead of removing it and compromising the envelope of protection it offers the house .... I've instead used the cementboard on only that wall.
The upper section of that wall won't be covered with a waterproof membrane.

There is no existing drain pipe yet, which makes it easy to position the drain. The pipe will be connected from underneath by the plumber at a later time.

A sheet of poly and lath has been attached to the floor in preparation for the mortar bed.
Fits nice!

You should be able to get at least 1-1/4" of mud under that drain.
Because this drain isn't attached .... it will be very easy to adjust.
Throw in some mud and get started.

Notice the lath over the curb. This will be mudded after the mortar bed in the shower is complete.
I've set the drain first, and then start to build my screed a good 1/2" higher than the drain.
The mortar bed is complete
Next the curb will be mudded.
Pick a wall and get started.

Everyone will do things differently depending on various factors. I'm starting with the walls because I want to finish ALL the Kerdi in 1 day. If I did the floor first I'd have to walk on it in order to do the walls or let it set up and come back the following day.

Use un-modified thinset mortar as your bond coat both to bond the Kerdi, and to bond the tile to the Kerdi membrane.
It's also important to waterproof the niche.
I've applied Kerdi to the floors, corners and curb. This shower is now water tight.
The wall without the Kerdi is the wall with WonderBoard CBU under which is a vapour barrier. I have come up the wall only about 3 feet to create a waterproof pan, but have left this wall without the Kerdi waterproof membrane, because there is already a barrier behind the wall.
1 vapour/moisture barrier is usually enough. It's been said by some that 2 vapour barriers could possibly cause a vapour lock.

I believe that no compromise should be made to the original vapour barrier of your home. I also believe that a waterproof shower should be exactly that .... waterproof. The exterior wall where most of the concern lies, is usually only about 3 or 4 feet, so when weighing the pros and cons .... I honestly don't feel vapour lock is even remotely possible.
I truly believe MORE DAMAGE may be caused if one or the other is omitted from the installation regardless of the materials used in its construction.
A positive slope will effectively drain water from the shower and prevent pooling.
Loose lay a few sheets of mosaics to figure out where everything will line up.
One of the nice things about the Kerdi drain is that the cover plate/insert moves from side to side in any direction to allow for corrections to accommodate the tile.
I'm using an old grout float to tap the tile into the mortar.
Yes ... use a lot of mortar around the drain!
You see how the mortar is coming up through the ring? Well that's still not enough mortar ....
Use the trowel to cover the ring completely.
I'll let the floor set up and start the wall tile next.
I had to install another layer of Wonderboard on the top (roof) of the niche (not shown in a photo) so it would drop down to allow for a continuous factory edge on the wall tile.
I used HardiBacker for the bathroom floor area.
Freshly grouted.

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