shower floor materials and kerdi questions

16 years ago

Gosh will I ever stop asking questions? Soon I hope!

So, with help of Bill, Mongo and others, it looks like my shower floor will be mud job plus kerdi, or possibly the kerdi pan (I think it will be decided after we demo and know if the drain location is OK or not for kerdi pan).

What material(s) should be specified for below the "mud"? One layer of 3/4 inch thick exterior grade plywood?--that's just my guess. Anything else?

I'm all set with the other floors (plan to use ditra) cause Schluter is pretty specific in their instructions.

Also, is there anything in the Schluter instructions that you feel could be done better or differently?

Mongo, what is "CDX" plywood?

Thanks again!

Lainie

Comments (4)

MongoCT
16 years ago
Continuing with my complete inability to be brief and concise: ;)

Plywood has four typical face grades; A, B, C, and D. "A" and "B" grades are the best, with "A" having no flaws in the surface veneer, it's good for stain grade cabinetry. "B" has a nice finish, but can have some patches in it to get rid of knot holes in the veneer, it's suitable for paint grade.

"C" and "D" are lesser grades, they are quite a bit rougher than A/B. The "X" refers to the glue being used to glue the veneers together being an exterior rated glue. The glue should not weaken when wet, allowing the plywood to delaminate.

So, for cabinetry or furniture, you'd want AB plywood. For house framing (subfloors and wall/roof sheathing, CDX is what you'd want.

As to the shower floor, 3/4" CDX ply is fine. If the subfloor were wood planking or 1/2" ply instead of 3/4", I'd add another layer of ply on top to isolate the wood planks from the deck mud or to strengthen the 1/2" CDX, depending on which you have.

So once you have your plywood subfloor in place:

On top of that I put down a "slip sheet". I use 6-mil poly, some use tar paper. Staple it to the floor, just enough staples to tack it into place. If there is any radiant floor heating under the shower, don't use tar paper. Instead use poly.

Over the poly use expanded diamond mesh, that gets nailed to the floor right on top of the poly. Overlap any seams and work to get the mesh flat so there are no "pops" in it when you walk on it.

The deck mud then gets packed on top of the mesh, pack it in well and build it up to the required thickness and slope.

Mongo
lainie55
Original Author
16 years ago
As usual, thanks so much! I see you re-posted the fantastic installation demo, too. I actually printed that whole posting, a few months ago.

Hey Bill, if you read this, I occasionally buy plants at Filanowskis, a stone's throw from your old window-shattering-from-the-copters house. I can see why you like Maine better, but I really love Connecticut (except the people are a bit friendlier down in Pennsylvania where I grew up).

I time almost all my travelling to avoid "rush" hour, but if not, I often take back road routes. I'd rather drive 30 mph in peace than stop and go on the highways.

Lainie
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Thank you Mongo for the explanation. It came just in time. I just had two other tile guys come in today and YOU WILL NOT BELILEVE...okay you pros out there probably will believe...what I heard today. When I mentioned what the original installer said, I think David you called it laziness, Mongo you called it uneducated. Here's what I found out. I had two additional tile installers out today. I was still not hearing what I wanted to hear when I asked for details about their process, esp. regarding the moisture barriers behind the cement board and the membrane on the shower pan floor. The last guy seemed very knowledgeable and I said to myself, I've got to come on out and just point blank ask because I am not getting anywhere. He said the same thing about cement board as the previous guy, but at least HE mentioned, taping those seams of the cement board with a mesh strip and thin setting it. So far so good. I asked about some other moisture barrier for the framing before cement board. He said they use a poly liner thing behind the cement board on the exterior wall. They don't normally do it on any other wall but they could... no problem. He mentioned some of the new boards that are lighter and made of foam, but he said they don't use them. Same deal, unproven and he would prefer cement in his own home. We talked about the shower pan membrane and he too talked about sand mix, membrane, build slope and tile. I finally came out and said, "I read somewhere the membrane should be put on a slope or something." He said we generally do it flat but what you are talking about is the pre-slope. He KNEW ALL ABOUT IT! What he said next floored me. He said yes in the Highland Park area we do a preslope. They have million dollar homes there. Not to say your house is not nice, but that area has more restrictions. Mongo, David and Bill...he described the steps just like you said...I guess my less than million dollar house didn't warrant the "correct" installation technique. :-( He even said why it is better to put it on the preslope, but I guess "cheap" houses don't get the extra steps. LOL I asked him about the membrane placement and he described what I had seen in the Harry Dunbar website. He did say he goes up about 8" on the walls, not 12 inches. He did say doing the preslope would make the shower pan area higher, but I told him I did not have a problem with that as long as the membrane was on the preslope. He did not have any problem doing it, but I am sure it will be reflected in the estimate he gives me. :-( Thought you guys would be interested in what I found out today. Thank you so much. I definitely will not be using the first guy.
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bill_vincent
16 years ago
I assume that's what used to be Gloria's over by Plains Rd. and Rte. 1?
lainie55
Original Author
16 years ago
Well, talk about off topic! (sorry everyone else!!)

No, I think Glorias is still there. Filinowskis was (or is) very close to the Wheelers....Exit off the Merritt. I don't even think they had a sign at the end of the driveway, very low key, more like a wholesaler. But many greenhouses filled with plants and very low prices.

Gosh, irrelevant now anyway! And I stopped going there cause I cut back on volume of planting in recent years.

Lainie

shower floor materials and kerdi questions

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