Travertine over 3/4 inch osb

[Yankfan7]

I am going to lay travertine tile over new construction 3/4 inch osb board. The floor joint are engineered web type. What do i need to do in order to start laying tile?

[jadnashua]

Unless the trusses were designed with stone tile in mind, they are probably rated for L/480. To use natural stone, they would have needed to be specified at L/720, which is easy during the design stage, but may not be possible after the fact. Then, assuming they are in fact L/720, you need a second layer of ply, at least 3/8" thick, nailed with the ends offset and the joints not lined up. Then, a decoupling (could be a cement board or a decoupling membrane such as Ditra from www.schluter.com). Then the tile. this also assumes the spacing between the joists is within specs for stone tile. Deflection has two components - the subfloor and their support structure. Both must meet the L/720 specification. The second layer of ply is to isolate the joints at a truss or joist which act like mini-levers upon deflection - the second layer bridges them and negates the effect. You could almost certainly use a ceramic look-alike, but may not be able to use real stone. Check out www.johnbridge.com for further help on tiling.

[Spaceman Spiff]

Be sure to nail and glue the ply to the OSB to increase the flex resistance. I have also seen 1/2" concrete board glued to the OSB, but only on L-480 floors.

[jadnashua]

Be sure to nail and glue the ply to the OSB to increase the flex resistance. I have also seen 1/2" concrete board glued to the OSB, but only on L-480 floors.

What you have seen does not mean that it meets the TCNA guidelines! While you can glue the second layer of ply, and it can help, doing it incorrectly can make the floor more susceptable to failure. The glue joint needs to be made with a water resistant full-spread glue like Titebond. Failure to get a full contact and coverage will give you grief. Generally, you are better off just providing the proper layers, and installing them per the guidelines.

CBU is never a valid means of stiffening a floor - the floor must be sufficiently stiff prior to it's application. And, nearly all of them require they be bedded in thinset, not to anchor it (the fasteners do that) but to fill in any minor imperfections and provide 100% support. In normal use, the cbu will move with the tile and the areas around the fasteners will be reamed out slightly because the wooden structure and the cement products expand and contract at different rates. CBU will bend over time to conform to the static shape of that that underlies it...it doesn't have all that much resiliency (no decent spring), so should not be included in any structural consideration other than its additional weight.

FWIW, the person involved decided to go with a ceramic look-alike because the trusses were not designed for L/720.

[Spaceman Spiff]

Sorry about that, I was looking up designs in the Natural Stone and Marble Mason's Association installation manual. Thought that would be a good place to get information on how to install travertine. What is the TCNA?

[jadnashua]

tile Council of North America...they have a testing lab and set the industry standards generally accepted for installation of tile on the continent. they also run a school. WHen a tile has a wear rating, they get it from these people because they submitted it for testing. www.tileusa.com Their handbook is the gold standard on how to build a shower, etc, and is a good reference to see if your contractor has a clue on how to build one that works. Note, there are numerous approved ways, so you don't have to follow one way that will work. You just can't take shortcuts if you want to guarantee it will last. same about preparation and installation of tile for floors, walls, etc. A tile installation can be a lifetime installation, discounting changes in style or desire.

[Spaceman Spiff]

Awesome info, Jim. I'm an architect and always looking for a better design to make it last longer. I have some good tile books, but I'll look into getting the TCNA. It's best if I have a published assembly to cover my butt if the system should fail... The Natural stone and marble book has been a great resource for attaching stone products to all sorts of surfaces. It will be great to have one for tile too.