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Unread 08-09-2014, 01:34 PM   #1
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Starting complete bathroom reno with curbless shower question w/ kerdi line

Hi All,
First time posting, although I've read lots here and appreciate the tons of advice already found. Unfortunately I have yet to find exactly what I'm trying to do with my shower.

We are remodeling a 1954 pier and beam master bath on the ground floor (good access to everything underneath). It's demo'd down to the floor joists. Due to foundation issues in the past, floor joists had been replaced and some sistered in this area, thus I will be moving them around to better suit the new bathroom. Rest of house is (what looks like) 3/4" tongue and groove subfloor with hardwood on top of that. I'd like to keep the bathroom floor flush with rest of house when completed (tiled). We (wife and I) are taking over a closet that was adjacent to the old bathroom and will use this space for the shower. Our plan is to have a curb-less shower slope away from the bathroom (into the old closet space) and use a line drain at the far wall. The Royal "We" (me) had thought I could replace current 2x6 floor joists with 2x8 or 2x10 joists and perhaps double them up or additional spans to get extra strength and cut the slope of the shower into the top of the joists. I'd lay ply or OSB sub-floor on the joists, Kerdi, and tile. Seems good until I add the use of a Kerdi-line drain (which due to this site am now considering ASO instead). Every install I've seen of the drain has it significantly higher than the sub-floor due to the foam stabilizer that goes around the outside. Doesn't seem like I'll have room for adequate joint strength plus slope, plus drain height, plus keeping floor level with the rest of the house. Shower will be 38" wide by 44" deep, thus 44" to get needed slope. Any thoughts? Can this be done? Let me know if I haven't given enough detail and thanks for all the help! I've learned plenty here before even posting.

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Unread 08-10-2014, 02:43 PM   #2
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Welcome Jeremy.

If i understand you correctly, you should be able to reframe the shower area to allow for the shower floor you desire. I'd lower the whole shower area to allow for a sloped mortar bed over the subfloor. You can add new posts/beams below and turn the joists if necessary to accommodate the drain, the lowered floor joists, plywood and sloped mortar bed.

"the road to hell is paved with osb, mastic, pre-mixed latex 'grout' or 'thinset', "
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Unread 08-10-2014, 07:38 PM   #3
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Thanks for the response Dana!
I'm trying to avoid a mortar bed altogether since I can slope the subfloor. The whole shower isn't that large and I can put lots of support under it so I wouldn't think it would be too springy to tile over. My big problem is just getting 2" of drop between the floor and drain when the Kerdi line drain sits so high above the subfloor.
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Unread 08-10-2014, 08:44 PM   #4
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What Dana said.

Mud bed are cheap to build and provide a effective means of ensuring properly sloped and water proofed shower floor. You can water proof the mud floor using a membrane like Kerdi or an applied water proofing solution like aquadefense or redgard. If you are planning on a Kerdi drain then I would go with the Kerdi membrane over mud.

How were you planning to water proof your shower using a sloped wood floor?

Last edited by PC7060; 08-10-2014 at 08:50 PM.
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Unread 08-10-2014, 08:53 PM   #5
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Welcome, Jeremy.

I'd recommend you rethink some of your plan.
Originally Posted by Jeremy
I'd lay ply or OSB sub-floor on the joists, Kerdi, and tile.
Schluter won't condone such an application as plywood is not a suitable substrate for Kerdi. And even if you were to install a suitable CBU over the plywood subfloor, I don't think you'll have much of a chance of making the height accurate enough to match up with any line drain with which I'm familiar. I suppose it's possible, of course, but I think you're making far, far too much work for yourself when making a sloped floor from deck mud is so simple and inexpensive and you can make the level exactly what you need for your drain.

I don't know what an "ASO" might be.

I don't think it's realistic to plan a 2" drop from the curbless entry to a drain only 44 inches away. That would be more than 1/2" per foot of drop, which even exceeds some code requirements. And if you were to use larger tiles you'd be creating a bit of a slip/fall hazard in there, I think.

You say you want the shower to be curbless, but with only 44" to the entry opening, I think you'll hafta have a door, and for a door you'll hafta have at least a small curb or hump at the opening for the door to operate properly.

Building a curb there would allow you to have less slope, keeping of course the minimum of 1/4" per foot, while still meeting the code requirement of having the drain 2" below the curb top.

If you want either that dramatic slope or a drain less than 2" below the entry threshold, I'd recommend you talk to your local code compliance official before making your final plan.

My opinion; worth price charged.

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