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Unread 01-29-2012, 10:14 AM   #1
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clarification needed on mortar bed shower construction

After reading/reasearching quite a bit on this, have some questions that I would like further clarified:

1. Some talk of using tar paper or poly behind CBU. Is this to go up the entire wall behind all CBU, or just for the first couple feet off the floor? One technique has just the shower pan liner going up a couple of feet off the floor, with no felt or anything else behind CBU--Im confused about this: is this PVC or liner the same thing and serve same purpose as felt does? Or is the felt behind the CBU diff from the pan liner being tacked up a few feet above the floor? I was planning on modeling after the mortar bed technique given by ontariotile/north american tile that can be readily found online. However they dont state or show they put anything behind the CBU except for tacking the pan liner onto the studs about 2 feet up the wall from the ground. Are they missing something here or doing something wrong or is this an older technique?

2. How far off the panliner should the CBU be? How large of a gap?

3. Havent found any discussion about how high the CBU has to go up the wall. If shower head is at 6 feet, can it just go that high or should it go to ceiling? Some say they would have nothing but CBU in any tiled shower on all the walls, but there are numerous showers where the tile stops at ~6 feet, and then have normal dry wall after that to ceiling. I find it odd that one would need to put CBU all the way to the ceiling, especially if water exposure is only limited to a certain area. Just like with surrounds for a tub/shower combo. The top of the surround doesnt go to the ceiling. So why do several people say they would never have a walk in tiled shower with anything but CBU on all the walls?? Whats the general rule concerning how far up the wall to put CBU for a walk in tiled shower?

A little clarity on these issues would be very helpful. Thanks

Last edited by rob27; 01-29-2012 at 10:20 AM.
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Unread 01-29-2012, 12:01 PM   #2
Tile nub
Join Date: Dec 2009
Location: Apple Valley MN
Posts: 113
You need to do some reading in the library section on shower construction.

The first thing you need to realize is tile and grout alone are not water proof. You should be able to take a shower in the newly constructed shower and have all the water go down the drain, without any tile on the wall. CBU isnt water proof either, water that seeps through it needs to be routed into the pan and out the drain.

Waterproofing comes in 2 varieties, behind CBU (plastic or tarpaper), or surface applied (membranes like Kerdi, or paint on like redguard / hydroban), how each integrates to the pan liner and drain junction varies. water proofing should go to the shower head height at the minimum.

The library will help you ask the right questions once you decide what you want to build.
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Unread 01-29-2012, 12:19 PM   #3
John Bridge
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Welcome aboard, Rob.

CBU only needs to go to the shower head unless it's a steam shower. Some sort of moisture barrier/retarder behind the CBU or, and I mean or, some sort of waterproofing on the inside face of the board -- one or the other.

The vinyl liner goes about three to four inches above the rough curb and wraps over the top of the curb with special vinyl corners at the ends of the curb.
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Unread 02-05-2012, 07:59 AM   #4
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how much deck mud?

At the stage of doing the pre-pitch mud floor for shower. Doing a 5:1 sand to portland mix. Wondering how much I will need approx for a 44" X 55" shower floor? Dont want to not have enough on hand mixed when start and have to run out and buy more. Have a 94# bag of portland and (2) 60# bags of sand and assume this is more then enought cement at least. From the experience of those that have done shower floors many times, will I run thru all these bags in making up my mix? Any info on how many lbs of each is typically used on a shower floor this size would be helpful. Thanks
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Unread 02-05-2012, 08:07 AM   #5
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Deck Mud Calcculator

Please use this thread for the remainder of your questions for this particular project. It helps us help you. Thanks!
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Unread 02-05-2012, 09:54 AM   #6
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