Andy

[Andy84012]

Hi newbie looking for help and suggestions.
The plan is total bath renovation. Figured my deflection rate at 200. The facts, joist are 13' - 1.5" - 7.25 on I beam steel and 2x6" sill on concrete block. The floor is blocked, if blocked is wood angeled at 45 degrees and placed in an X pattern next to each other between all joists and happen to be directly under the bathroom in the middle of the area to be tiled. I am not sure what sistering the joist is or if necessary? In the bathroom floor will be striped down to existing plywood 5/8" thick unknown type of wood. Plan is to add 1/2" plywood ACX, BCX or CCX (which is better?) leaving 1/8" between sheets and 1/4" around perimeter. Glue Tite bond? What type of screw? Read about installing Hardi backer board on their web site. If I use this the floor will be approx. 1 7/8" including the travertine tile I want to use 18x18x1/2. Then read in a post about using Ditra to reduce heigth. What is it and how would you install it? What transition would you suggest for transition from travertine to oak in hallway? Where to get it? The new plywood if this means anything will also be put under the new tub. Phase two replace what ever is on the wall around tub with Hardi backer board and tile? Your thoughts and answers to my questions would be greatly appreciated, this is my first time tiling!!!

Thanks Andy

[Davestone]

Wow, back up brother.The deflection needed for travertine stone is 720...a loooong road ahead of you.Sistering is nailig a joist to another one,this doubles them up.The cross bracing is for keeping twisting to a minimum.How far apart are your joists?At this point i can't see you tiling that floor unless you put a beam under the joists to cut your span in half..maybe build a closet.

[Andy84012]

The joist are 16 on center, the underfloor is exposed. What type of beam or sistering could make this possible?

Andy

[Andy84012]

Suggestions on how to get the deflection rate high enough for stone? Keep in mind that the joist are open and are able to be accessed.

Thanks Andy who doesn,t want to be stuck with vinyle.

[Mike2]

Andy, you've mentioned your joists (2x8's) being 13' long; however is that also the unsupported span? Or to ask that question a different way, it there anything providing support for those joists between the steel beam at one end and the 2x6 sill plate 13' away at the other end?

For a natural stone floor using 2x8 joists you'll need to reduce the unsupported span to something in the neighborhood of 7 feet. Is that doable?

[Andy84012]

Currently there is a 1/2 bath underneath the upstairs bath, there are support walls for that bath that do not go all the way to the joists(things in the way) but I could add 2x4 from the top cross member of that short wall to the underside of the joists. That wall nearly cuts the up stairs bathroom in half,so support would be in the middle of the bathroom. Would increasing the subfloor thickness and using ditra and the above reduce deflection enough to support stone

Thanks Mark

[Mike2]

Sorry but you cannot reduced joist deflection by adding more plywood alone. You will need two layers of plywood on the floor for natural stone tile BUT in addition to that you also need to reduce that unsupported joist span. If you can use one of those 1/2 bath walls on the first floor to support of those 2nd floor joists and cut the span in half, I'd say you've lucked out.

[Andy84012]

Thanks Mike
I think your right I did luck out I can extend that wall at the points were it meets the joists which would cut the span in half and the basement floor is concrete no give. Still wondering about Schluter.com/docs/H173ME.pdf claim that there product ditra will prevent cracking or grout crumbling. Any experience with this product. It apparently allows for small movement as I read it.

Thanks Mark

[Mike2]

Ditra is a wonderful product and yes, I'm quite familiar with it. It will do all those things stated on the Schluter website however, Ditra can not and will not protect a natural stone tiled surface from cracking when the joist's have a deflection rating of 200 or so.

You must get that deflection number up to L/720. In your case the bathroom wall down below offering mid span support will do that. And you will need to get your sub-floor combined thickness up to 1 -1/4. Then Ditra can do it's thing.



By the way, have you checked out the Deflecto tool found near the top of this page. If not, go check it out.