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josie235 05-16-2011 06:04 PM

Josie's Bathroom remodel
Hello to all. My husband and I are very experienced DIYers, and have done a fair amount of tiling, but are taking on a bit more with our bathroom remodel. I am so grateful to the wealth of information on this forum and have already made several changes based upon information on this site.

New bath includes full shower using Schluter system- green board walls with Kerdi, Schluter curb, base and drain. Walls to be tiled with porcelain tile with honed quartzite accents and shower floor is sliced marble mosaics. Bathroom floor is 12" x 12" tumbled quartzite. These are giving me the willies and th first set of questions.

We have a log home, so structure is a bit different from what I have been used to in prior houses. Instead of floor joists, we have trusses- 24" on center. 3/4" plywood subfloor over that. The deflection table didn't address trusses, but the floor clearly needed improvement. We have added 3 lolly columns under the floor and added 2x6" what I am calling "strengtheners". Laid 1/4" hardibacker over modified thinset this past weekend. This floor is solid now.

Onto the quartzite concerns. I have washed and face-sealed the stone. They are varying thicknesses and usually do not have flat backs. :crazy: (You pros probably feel I should defer this work to a pro, but I love a challenge).
1. When I am ready to lay the tile, what are the best practices for this type of stone?
2. Are there some obvious "gotchas" that you pros have discovered?
3. Do I compensate for thinner areas on a single tile (stone) by adding additional thinset via backbuttering?
4. Any other tips ?

Thanks again,

dhagin 05-16-2011 07:33 PM

Welcome Josie, :)

I'll try to get some of the structural stuff started...

So, were the trusses designed for a deflection under load of no more than L/720, the maximum for stone? Industry standards for stone requires a minimum of 2 layers of plywood, OR reinforced mortar bed over proper joists/trusses 16" OC max. Since you have 1 layer of ply and cbu over trusses 24" OC, you may want to consider Ditra XL over the cbu. But first, verify the trusses are designed to support the stone load. :)

Link to Ditra Handbook on the side of page --->

josie235 05-17-2011 06:43 AM

Thanks for the help Dana.... I am not sure we have access to the specs that the trusses were built under. The company that sold the log home kit has been bought out. Since we were concerned about the flexing with the truss, we consulted with a well-respected builder in our area. He suggested adding 2-2x4's, sistered with a piece of plywood to act as a header under 3 lolly columns (after jacking floor up to level height). Mr. Josie also added some 2x6's as blocking under the ply subfloor to allow us to screw the joints in subfloor down more securely.

So, the trusses in question span 11', with the area in the bathroom to be tiled at ~ 5x8'. (They run parallel to the 8' length). After the structure work and the screwed down cbu, this floor feels extremely solid. I did a lot of jumping around on it and objects on the floor never moved. Are you suggesting we still add Ditra?

Houston Remodeler 05-17-2011 07:11 AM

My thinset of choice for this floor is 4XLT from Laticrete. It will be able to handle the different thicknesses well.

Also know there may be some tiles that are so bad they can't be laid next to each other or at all.

josie235 05-17-2011 09:32 AM

Paul....thanks for the thinset recommendation. What is the advantage with this particular thinset? The tile store gave us Maipei Ultraflex 2 with polymer. Should we switch to the Laticrete 4XLT?

And on the stones, as I face-sealed them, I sorted by "group A, B and C", with C being the tiles either used outside in the garden as left-overs or under the vanity. Many of the A's are not too bad and as a novice with this type of tile, I had planned to take the extra time and dry lay them first checking for thickness and flatness.

AdamP 05-17-2011 09:42 AM

Hi Josie,
Did you mention that your shower was done using the Schluter-Kerdi system?

You're going to need an unmodified thinset to stay within warranty, Maipei Ultraflex 2 with polymer sounds like it is a modified thinset. I'd double check with an expert before you use it.

EDIT: Or are we talking about the floor?

dhagin 05-17-2011 10:54 AM

I'm not quite gettin what additional structural work you've done. Could you post a few photos of this to help me out? :)

josie235 05-17-2011 11:06 AM

Adam, we have not done the shower yet, but will be using unmodified thinset with the Kerdi. In fact, we have labeled each bag with its respective use to keep it all straight.

So to add, yes, the Ultraflex 2 was for the floor only.

josie235 05-17-2011 11:07 AM

Dana, I will post some pics tonight. As a newbie to the forum, I had to have posted some non-pic posts first before the system will allow me to upload any images- it seems to be the spam/porn checker...:rolleyes:

Dana, after seeing your post and checking back with the tile store, we are now picking up Ditra and will hopefully lay it tonight. I'll get pictures posted also to help you understand. So glad you saw this post! Thanks again.

dhagin 05-17-2011 12:19 PM

Ditra XL, which is what I recommend? or regular Ditra? :)

Also, you can upload photos from your computer any time. Use the 'Manage Attachments' button below the reply box.

josie235 05-17-2011 05:26 PM

3 Attachment(s)
Ugh....so while unsuccessfully multi-tasking between my crazy day job and this project, I missed the fact that the 2 different thicknesses of Ditra are differentiated between by names, not just dimensions. So, as Mr. Josie headed to the tile supplier to get the Ditra, he came home with Ditra, as suggested by the owner of the shop. (They only recommend Ditra XL when butting up against hardwood floor). 1/8" of Ditra results in a total of 1 1/8" below the stone- not counting thinset layers.

Hopefully these pictures will assist your understanding of the additional support below the subfloor. A bit messy with all the water and wires running through the trusses, but you can see most of it.

3 lolly columns

dhagin 05-17-2011 08:57 PM

I'm not familiar with that type of truss. I wonder if it was site built???

Supporting trusses with a small beam like that is not something I'd have a lot of confidence in. Trusses are typically designed to be supported at specific bearing points. When you add bearing points that weren't designed in, the entire truss design is changed. Not sure how that will hold up long term once the flooring loads are placed on it??? I recommend getting a second opinion from a licensed engineer on that.

Both the 2011 ANSI Standards and TCNA Hanbook recommend 2 layers of plywood or a reinforced mortar bed over proper joists/trusses to support a stone installation. I think you're rolling the dice with what you have so far, and what you're planning. To try to better your odds, I'd add more blocking under the floor. I think I'd put 2x blocks 12" OC between the trusses and glue them up to the plywood in addition to nailing/screwing to the trusses. :)

josie235 05-18-2011 06:39 AM

This house was a log home kit, with these trusses supplied. I was not around at the time of build, so do not have a lot of information.

With that said, when we consulted with an area builder (he is also an engineer), he specifically suggested placing this beam where the truss's cross-bracing meets in order to push up and evenly distribute the pressure in the correct places on the truss. We did feel like we were doing due diligence by consulting with him, but at the time we were unaware that laying a stone floor carried more stringent specs than laying a porcelain tile floor. (While my research missed that fact, I am a bit frustrated that the tile supplier who sells only tile/stone etc. did not mention this fact- I expected a bit more info since we were not buying from Homer's).

So, onto your suggestion to fix our current predicament:
I think I'd put 2x blocks 12" OC between the trusses and glue them up to the plywood in addition to nailing/screwing to the trusses
Can you be more specific? It's not clear to me if you are suggesting cross bracing between trusses? Or adding more blocking , but doubling the layer, like we have already done? (Current blocking is screwed up flat to both subfloor and truss.

Thanks again for your sage advice...

dhagin 05-18-2011 08:06 AM


Originally Posted by Josie
Mr. Josie also added some 2x6's as blocking under the ply subfloor to allow us to screw the joints in subfloor down more securely.

This post and your last photo above look like you have 2x6 flat blocking at 4' OC? Correct me if I'm not seeing things correctly.

Truss issues aside, I'd add more blocking like you already have. Since you already have cbu down, i'd just nail/screw this new blocking to the trusses and glue up to plywood with construction adhesive. :)

josie235 05-18-2011 11:47 AM

Thanks for all the information Dana. We are heading out for more 2x6's to do just that.

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