I am working on completing a bathroom and shower that should have done a long time ago. Unfortunately life has got in the way of that happening. :-)

I am quite handy in many areas and a bit of a perfectionist at times. That may have as well contributed to the long delay of getting to complete this bathroom.

I would appreciate any critique, suggestions, reccommendations on my planned approch

Here are some details of the structure:
1. The bathroom is part of a new contruction additon that we built in 2005.
2. The floor for the overall structure spans 22' 6"
3. The floor joists are 14" TJI joists with glued and nailed 3/4" tonge and groove plywod on top.
4. The bathroom is along an exterior wall and is 13' 6" x 6'6".
5. The shower occupies one end of the above dimension and is 3' 2" x 5'. There is a seat inside it as well.

General bathroom plan
I am planning on completing the bathroom with 12 x 12 natural stone tile using the following method:
1. apply 1/4" plywood on top of sub-floor (lots of screws)
2. apply thinset mortar
3. apply DITRA,
4. more thinset mortar,
5. install stone tile
6. seal
7. grout
8. seal grout

Shower
1. apply 1/4" plywood on top of sub-floor (lots of screws)
2. apply thinset mortar
3. apply DITRA
4. build preslope on top of DITRA
5. install durock concrete board for walls, seat and ceiling
6. apply KERDI to all surfaces (mortar, KERDI membrane, seam tape),
6. more thinset mortar,
5. install stone tile (mosaic on floor and various sizes on walls/ceiling based on design from my wonderful wife)
6. seal
7. grout
8. seal grout

Any input would be greatly appreciated.

Thanks
George

For the first part, you need to change the 1/4" ply to 1/2" ply. 1/4" has no place in a stone installation. But first you need to check with the manufacturer of those joists and make sure they are rated at L/720 for deflection. Any less than that and they won't support a stone installation.


For the second part, same thing, no 1/4", 1/2" instead. You won't need Ditra in a shower. If you're installing Kerdi, you should follow their recommendations which require no pre-slope, just one single mud bed at the time the drain is installed. And you can use regular sheetrock for the wall, durock or any CBU is unnecessary. By the way, the sheetrock needs to be installed before the mud floor, no matter what method you use. On #6 (the first #6, that is) I'm assuming by "seam tape" you mean Kerdi band? There will be no tape covering any seams in a Kerdi shower.

Unless you are looking for a certain height to meet up with the rest of the flooring, a second layer of plywood is not necessary. If you must use 1/4 inch ply, use Halex which has the strength of 1/2 inch softwood ply. Just apply Ditra directly to the 3/4 inch ply.

Kman is absolutely right on using regular drywall in the shower, but the curb should be stacked 2x4's covered with cement board. I like to use very dry wood for this, so there are no shrinkage issues. The bench should also be covered with cement board not drywall.

Use modified thinset to attach ditra to plywood, but standard thinset to set on top of it.

Pete, he's putting in natural stone, so the second layer is required.

If you have TGI's the standard design criteria has normally been L480. Unless a higher deflection was asked for at the design stage, that's what you should have.
The unfortunate part is there's no way to beef that floor up without geting it re-engineered.

1/2" extra layer of plywood may marginally make it better but those floor systems are prone to vibration and be quite bouncey.

I honestly don't know how Schluter gets away with the spec for TGI floor underlayment.

I would check with your architect or builder to see if they could provide the technical design specifications.

First of all, thank you very much, all of you for all of your input. It really is fantastic that there are people that are so passionate about things that they take their time to help others who they don't even know :-).

Kman,
Although I am looking to use the Kerdi waterproofing felt I am not able to use the Kerdi drain as the shower is over top of a garage that has spray foam and drywall already applied on the ceiling which makes the under-floor space of the shower inaccessible. There is a conventional shower drain that is already glued in place to the drain pipe, which is really what I have to work with.

Because of that I was looking at working with a modified version of http://ontariotile.com/preslope.html and substitute the roofer's felt and diamond lath with the DITRA as I was going to use it for the rest of the bathrom and in other parts of the house when I eventually get to doing my kitchen and redoing another bathroom...

Based on this, does the wallbaord still go in first or after the preslope? And yes, the seam tape implied the Kerdi band.

As per RC's input, I believe that my joists are going to be rated at L480. I checked one of the shipping receipts and the joists are 14" LPI-42 I've been poking around their website looking for some indication that I stand a chance of them being rated to L720, but I'm not sure that's looking too hopeful. I will dig up the drawings and see what the floor engineering indicates. If it does specify L480 which I'm expecting....

...It sounds like increasing the 1/4" ply to 1/2" ply is not going to make a big difference as per RC's post, but it would increase the finished height higher than I would like it to be in the end. I actually don't think that I feel any bounce in the floor. I think that I feel more bounce on an 11' span in the original part of the house that's made up of spf 2x8 and 3/4" plank.

From what I've read in your replies (thanks again), right now I'm hoping that the fact that the subject area is closest to the point (where one would think) that there would be the least amount of flex on the floor. not sure that I am expressing that properly... The 13' 6" length of the bathroom is actually perpindicular to the orientaion that the joists run, so one would figure (I'm doing so at least, right now :-)) that there should be less movement there than there would be if the length of the bathroom was parallel to the run of the floor joists. I would expect that there would be more movement closer to/in the middle of the span than at the edges where it bears on structure beneath??

Pistolpete,
I actually have the Durock onsite already as it was ordered when the rest of the addition got drywalled. As long as it's not going to be harmful to the installation, I don't mind using it.

Not sure where this really stands right now. I might be painted into a corner as far as any hope of the floor not failing in the future, based on the material we are hoping to use? Would it be better if the tiles were reduced to smaller sized units? Do I roll the dice and see what happens?

Regards,
George

George, there is an adaptor from Schluter that fastens to your existing clamp style drain which makes it work like a normal Schluter drain. That would allow you to do a one shot mortar bed and Kerdi membrane.

As for the floor, Schluter's minimum spec for a natural stone installation requires a 3/4" subfloor with a 3/8" plywood underlayment prior to Ditra. Remember these are minimun requirements! They don't care what the spans are other than it can't have more then a 24" joist spacing. Schluter makes no references to deflection requirements, so if you want to chance an expensive stone install without metting their minimums,then thats your call.

It's not going to matter too much if the stone is smaller. That just means more grout joints which may crack if the floor system doesn't meet the required specifications.

You may need to do a porcelain tile install if you can't live with a height transition for the stone.

What? Randall, will you please explain that.

Jaz

Hi Jaz,
Schluter has obviously done their own testing with reference to joist deflections and feel the specifications presented in the installation literature to be sufficient. They do not get into any specific joist size requirements or span requirements.
When you read the installation spec's and look at the pictorials, the only criteria a customer is concerned with is, whats the spacing of the joists and how thick is my subfloor? If it looks like the picture then I'm good to go.

Don't you think there's something missing?

Maybe my explanation or wording is incorrect, but it's to the point. They don't mention anywhere that you need L/380 or L/720, size of joists or any criteria for meeting standard building codes. All too vague for the average Joe.

Randall,

Thanks for that. I grabbed a copy of the DITRA installation handbook and see that minimum specification that you're as well citing. I'll take another look a the elevations and see if I've got room for another 1/4" of underlayment bringing my underlayment thickness up to 1/2" on top of the glued and nailed down 3/4" tonge and groove plywood subfloor.

If I find some nice sloped marble/stone sills to use in the doorways this could work well to transition to the hardwood outside.

I may give Schluter a call to see who carries all of the inside and outside corners for the Kerdi as it doesn't look like the Depot does.

Any suggestions on building little niches in the shower walls to hold soap and other accessories? Or should this be avoided? Does anyone make prefab units that are all sealed up already or will I just have seal them up with the Kerdi?