Non Mud: All Kerdi & Ditra Bath on ply, 2x4's greenboard & drywall

[Dale Moore]

I'm a DIYer (first time with tile) trying to remodel masterbath with drop in acrylic tub (I finished framing the surround) and a new shower. I have purchased a Kerdi shower kit and planning on frameless glass shower sides and door. I'm wondering how wide must the curb be on the door side of the shower floor. NOTE: there are walls on 2 sides of the floor, and the 3rd side will have built in wooden bench seat (full width), so I only need the curb on door side. Would like to go as narrow as possible in order to save as much room in the shower as possible, but don't know if there is a limit as to how narrow it can be. I was fine until I read on your web site which quotes, "In showers with doorways (jambs), the width of the curb will agreee with the width of the jamb walls alongside the opening." I'm not quite sure what the "jamb wall" refers to. The Kerdi shower kit comes with a curb piece. Thinking of cutting it lengthwise down the center. Is that OK? Talked to someone at Schlueter who said it was fine as long as the cut was straight. What do you think? Any confusion you can clear up is appreciated.
Thanks,Dale

[Davestone]

He's referring to walls that jutt out and are connected to the curb..they're usually the width of a 2x4, and drywall, on both sides,about 41/2".If you cut that in half, and put the door in the center, you're only saving one inch on the inside..is it that critical?

[opiethetileman]

And if you narrow the curb the less sturdy it will be. especaaily over time if water wants to eat it

[John Bridge]

Welcome aboard, Dale.

My Kerdi curbs end up about 3 inches wide. You can do that with a 2X4 on edge (over a wood floor) or bricks on edge over a concrete or wood floor. I've never used the Kerdi curb. Not too sure about it split in half.

[Dale Moore]

Thanks Davestone, opiethetileman (Can I call ya Op?) and John-
All good advice.
Good point Davestone but it's tight (36" overall to work with) and I'd love the extra elbow room. I use to smack em all the time in the old shower enclosure. And you brought up a issue you could advise me on. I was considering the possibility of placing the shower glass walls as close to the outside edge of the curb as possible to steal what room I could. Is this a no no, structurally. I figured as long as I kept them directly over the wood 2x4's, I'd be just as supported as if they were in the center of the 2x4's. I don't feel visually they will look bad but I haven't seen them either. What do you think?

Op, I've been fairly assured by using the Kerdi membrane, water is not gonna be an issue for anything under it. Do you have a concern even with the using of Kerdi?

So I think I'll go with John's 2x4 idea which is a fair compromise. You did mention in your book you liked using 2x4's on end for a unique look, if I remember correctly. Maybe that can be done but Op' stability comment seems a valid one which may stop that idea considering the possible weight impact of the thick shower glass door and windows/walls. And my desire to place them on the outside edge of the curb as mentioned earlier to Mr Davestone.

Another question guys if I may. I'm fairly sure I know the answer from all my research but I still feel considerable qweeziness about. "It's OK to use Kerdi on green board and drywall?" And as I've gathered, it's Drywall or Greenboard, thinset, Kerdi, thinset, tile, grout, sealer. My concern is the 2 thinset layers do not provide the stability you would get if you were to put those 2 layers on traditional CBU or even the Hardi Backer or DuRock type backerboard. Even tho, I've learned the thinset is expected to be uncoupled from backerboard anyway. (I suffer from the "more is better" mentality.) Everything indicates, tho, those 2 layers combined with tile are as strong as one may need to succeed with a long lasting tile job. -Correct or did I fail miserably in my studies? Again, Thanks for your time. - Dale

[Dale Moore]

The beginning of this thread is from a previous inquiry. I included it here because I had comments plus more follow-up questions. I’m afraid many more may follow. How do I keep this internet thread current as I’ve seen in other threads. I apologize for my ignorance in the matter.


**************The New Stuff*********

Thanks Davestone, opiethetileman (Can I call ya Op?) and John-
All good advice.

Good point Davestone but it's tight (36" width overall to work with) and I'd love the extra elbow room. (I use to smack ‘em (elbows) all the time in the old shower enclosure.) And you brought up an issue you could advise me on. I was considering the possibility of placing the shower glass walls as close to the outside edge of the curb as possible to steal what room I could. Is this a no no, structurally. I figured as long as I kept them directly over the wood 2x4's, they'd be just as supported as if they were in the center of the 2x4's. I don't feel visually they will look bad but I haven't seen them either. What do you think?

Op, I've been fairly assured by using the Kerdi membrane, water is not gonna be an issue for anything under it. Do you have a concern even with the using of Kerdi?

So I think I'll go with John's 2x4 curb idea which is a fair compromise. You did mention in your book you liked using 2x4's on end for a unique look, if I remember correctly. Maybe that can be done but Op' stability comment seems a valid one which may stop that idea considering the possible weight impact of the thick shower glass door and walls. And my desire to place them on the outside edge of the curb as mentioned earlier to Mr Davestone. What do you think, John?

Another question guys if I may. I'm fairly sure I know the answer from all my research but I still feel considerable qweeziness about. I have researched: "It's OK to use Kerdi on greenboard and drywall" And as I've gathered, it's Drywall or Greenboard, thinset, Kerdi, thinset, tile, grout, sealer. My concern is the 2 thinset layers do not provide the stability you would get if you were to put those 2 layers on traditional CBU or even the Hardi Backer or DuRock type backerboard. Even tho, I've learned the thinset is expected to be uncoupled from backerboard anyway. (I suffer from the "more is better" mentality.) Everything indicates, tho, those 2 layers combined with tile are as strong as one may need to succeed with a long lasting tile job. -Correct or did I fail miserably in my studies? Again, Thanks for your time. - Dale

Little more background on what I’ve gone with so far based on my internet learnings. Mostly from this web site. I’ve deemed John an authority. Jump to string of asterics below if this doesn’t help or interest you.

Reason for fix, Fiberglass type shower pan cracked and leaked at drain rim which resulted in adjacent particle board under linoleum to swell.

I have ripped up all particle board. ( Wwwhy in a bathroom? ) Left with 3/4” plywood subfloor on 2x6 (5 1/2”) joist, 16” oc. Checked deflection rate on your site, Great thing you provide. (I sound like Yoda)
Added 3/8” plywood “sheathing rated” (hope that’s good) using subfloor rated adhesive smoothed out to avoid voids and screwed down with 1 1/8’’ deck screws. Gave approximate 1/8” expansion gap at all plywood butts and 1/2” gap on room perimeter. Polyurethane chalk applied to 1/8” expansion gaps.

Utilized self leveling cement for low point near plywood replacement area and all screw depressions for both subfloor and added plywood.

Made tub surround for drop in acrylic deep soaker type tub, no jets.

*** * * ** * * * * * * * * * * * *

Another question is do you see any issue with my tub surround not having cbu or plywood “skin” as its “joining” surface for the first layer of thinset and kerdi. I’ve made the surround with solid 2x4’s on the top side of the surround ( small deck ). At points and spans I’ve flatten and leveled as needed using self leveling cement.

I got the impression early on that slc was acceptable for thinset underlayment.

I’ve base this construction decision on my research of Ditra’s ability to be applied to plywood subfloor with SLC in the same manner. The 2x4’s are much more stable and, I feel, are just a viable.

I’ve been getting the feeling it’s always adhered to cbu or plywood and it’s the flatness factor thats warrants that. I feel I achieved that anyway with my 2x4’s and self leveling cement. Do you feel I should be OK or did I make a mistake somewhere in my assumption that this would work.

Also, I’m constructing a shower seat in the same fashion as the tub surround. 2x4’s and SLC on the horizontal plain. A fiber CBU will be used on the larger vertical plains. I find nothing about wood construction for shower seats which leaves me with concern. With you concurrence, I feel confident if I overkill it with double and triple layers of 2x4’s using deck screws and subfloor adhesive to the wall studs and upgraded subfloor, it’s not as good as a John Bridge “monument”, but more than adequate. -John????

Davestone, thanks for your jamb wall explanation. Your “jutt out” phrase made me see it. If I’m correct, this is a wall coming off another wall at 90 degree angle to form a portion of the shower enclosure that the curb would grow off of.

Many Thanks, Guys!! Dale

[jgleason]

Hi Dale,

Keep all your posts on this one thread. I'll merge your other threads into this one. Bookmark it (or save to your "Favorites") so you can find it whenever you want. As posts are added to it it will bump back to the top of the forum for all the world to see and comment on.

[jgleason]

Bumping to the top for Dale.

Dale, I found the two missing posts, I merged them into the wrong thread. Oops! All should be intact and on this thread now.

[Dale Moore]

I'm afraid I may have over stayed my welcome with the large thread of questions above, so i've been advised to try one or two questions at a time. So here's what i need to know ASAP. And first of all, i'm starting with the premise that it's OK to use Kerdi on both greenboard and drywall. With that in mind, is the progression: greenboard (or drywall), a layer of thinset, the Kerdi, another layer of thinset, tile, grout then sealer? I guess my concern is that the 2 thinset layers with the Kerdi will not provide the same strength and stability you would get when applied to traditional CBU, Hardi Backer or DuRock. I guess I don't calulate the 2 layers of thinset being very thick and therefore not very strong. Any help is greatly appreciated!
Thanks, Dale

[John Bridge]

O, ye of little faith.

Once the drywall is covered with thinset, Kerdi, tile and grout it will be very rigid. I don't worry about that aspect. Nobody's going to be walking on it. You are certainly welcome to use CBUs instead of drywall. The Kerdi process is the same.

I make wood benches in the Kerdi showers I do quite frequently. I build them super strong and cover them with 3/4 in. plywood.

Other times I use cement blocks and mortar.

[Dale Moore]

Thanks John

Another "faith building" question is do you see any issue with my tub surround not having cbu or plywood “skin” as its “joining” surface with the first layer of thinset and kerdi. I’ve made the surround with solid 2x4’s on the top side of the surround ( small deck ). At points and spans I’ve flatten and leveled as needed using self leveling cement.

I got the impression early on that slc was acceptable for thinset underlayment. I’ve base this construction decision on the research of Ditra’s ability to be applied to plywood subfloor with SLC in the same manner. The 2x4’s are much more stable and, I feel, are just a viable.

I’ve been getting the feeling it’s always adhered to cbu or plywood and it’s the flatness factor thats warrants that. I feel I achieved that anyway with my 2x4’s and self leveling cement. Do you feel I should be ok or did I make a mistake somewhere in my assumption that this would work.

THANKS for your feedback. -Dale

[John Bridge]

I'm not quite sure why you used slc or how you installed it over plywood. Did you use metal lath, and did you use slc primer? I'm not seeing it. Maybe post a picture for us.

[Dale Moore]

Hi John,

Sorry for the confusion. I didn't use plywood on the top surface of the tub surround. Just solid 2x4's screwed together to form to top plain. I used slc (with it's recommended primer) to attain a smooth flat surface in areas with a slight depression or where the 2x4's slight bullnose edging left a troft. Believing a smooth flat surface was required.

Do you see any issue not using the plywood. I'll work on a photo. Probably would help. But I think I've explained OK here. Clear as Mud. -Dale

[cx]

Originally Posted by Dale

Do you see any issue not using the plywood.

Yes. The dimension lumber you used for your top is strong enough, Dale, but it's not dimensionally stable enough, as would be the plywood.

If you just primed and poured SLC on there, I'm thinking you're still subject to some cracking. I'm not experienced with SLC, but I think you should check the manufacturer's instructions to see what they say about that application.

At the very least, I'd suggest you use an antifracture membrane on top of that SLC before you tile. The membrane manufacturer ain't likely to warranty the installation, but it might save your butt.

My opinion; worth price charged.

[Dale Moore]

Thanks for your time.

...not "dimensionally" stable.... ?!

if you mean flat and level, I leveled the 2x4's on "the bubble" and I used the slc to get that "flat plywood" surface feel needed for the first layer of thinset.

But I didn't pour. Just in certain areas I applied it using a flat trowel and spackle knives. The same manner as spackle is used to level drywall depressions and seam joints. I used "Dap Dondex Concrete Floor Leveler" and its "Bonding Liquid & Floor Leveler Additive". It says it's for wood subfloor. I just thought if it would work on the wood plywood subfloor than the wood 2x4's would also be OK.

The instructions also mentioned using this product as a repair for depressions and cracks and to smooth to a feather edge. I didn't feel this was too much of a stretch application-wise.

1.Do you still think I'm at risk of cracking?
2.Does this membrane add much to my demensions?(I wouldn't think).
3.Does it provide some kind of cushioning function/less stress on SLC?
4.Plus is the membrane necessary since I plan on using Kerdi thoughout the bath plus Ditra for the floor?

Thanks, CX!