Big Travertine Job [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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05-18-2015, 10:09 AM
This is my first post on JB so I hope it is not too long. Moderators, if there is a better way to post these questions please let me know.

I'm not a professional tile setter but I've set enough tile to be dangerous. I'm about to start on a 1600 sf job using large format, 1/2" thick travertine tiles set in a French (Versailles) pattern. This job is a little more involved than the others I have done.

1) I need to level a dining room floor that is out 1 3/8" in 10' and I have no experience with self leveling compounds. The Deflecto calculator does not quite offer the exact dimensions of my subfloor so I would appreciate your input on its suitability for this tile.

The floor is constructed of a 1 1/8" single thickness, T&G plywood subfloor on 4 x 6 (3.5 x 5.75 actual) beams sitting on concrete piers spaced on a 32" x 72" pattern. The room is 12' x 14'.

Two thirds of the room drops off uniformly from 0" to 1 3/8" in 10'. I plan to use a self leveling compound topped with Ditra as I don't know if Hardibacker can be used over SLC. The guys at Custom Building Products have recommended 2.5 metal lath, a generous coat of primer and they told me not to feather the SLC but instead dam it to at least 1/2" thick and then float it from there with their "Speed Finish".

The room is adjacent to the kitchen, which is already done so I want to match the level of the kitchen tile. This means I only have about 3/4" to work with. The good news is I don't need any SLC at the doorway into the kitchen.

a) Will this subfloor support the load?
b) What are your thoughts on the SLC application advice from Custom Products?

2) I will be doing a 42" wide staircase that has four 2 x 12 stringers and 13 steps (so fairly standard). My questions are:

a) Is this strong enough for 1 1/8" thick travertine pavers for the treads?
b) Do I need to install an underlayment like Ditra or Hardibacker?

3) I am also curious how experienced tile setters handle grout line spacing with the French pattern. I was mocking up a section as part of my preparation and I noticed that when two 8" wide tiles butt up against a 16" tile or an 8" and a 16" next to a 24" there is no room for a grout line between the two 8" wide tiles or the 8" and 16". I can't figure out how to get around it. How do you all handle this?

Thanks for taking the time to respond.

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05-18-2015, 10:57 AM
Welcome, Tim. :)

That is quite an ambitious project, given the size of the tile and the pattern.

Natural stone requires two layers of subfloor, so you would need to add a layer of 1/2" plywood over what you have there to meet standards. One would think that 1 1/8" would be thick enough by itself, and one could certainly tile over it, but the odds of it being successful are not near as high as with two layers. If I were doing this job for someone else, I'd want to make sure I didn't have to do it over later at my own expense. Also, travertine is one of the softer stones, which means you really don't wanna take any chances with it.

More importantly: you have a joist spacing that is not something we normally deal with. If you even had 24" spacing, I would feel better about your plan, but I can't honestly say your plan will work, even if you take my advice in the above paragraph. I know our former engineer said that ceramic tile would work under those circumstances with the proper subfloor installed, but not natural stone.

Regarding the SLC, you can certainly go that route as suggested, however I'm not sure why they told you not to feather the edge when all of their self-levelers advertise ( they go from feather edge to 2". I would definitely have a helper on hand if/when you get to that point. SLC of that quantity is not a one-man job.

First, I think it would be best to get past the joist subfloor issue. If we can't get that part straightened out, everything else is moot. Any chance you would be able to add some joists and bring the spacing down to 16"?

05-18-2015, 02:47 PM

Thanks for the quick response. I really don't want to raise the floor another 1/2" because I want a flush transition into the kitchen but I hear what you say. I will think about ways to stiffen the sub floor between the joists. I have access to them via a crawl space but I don't relish the thought of working under there. I will talk to an engineer that I know and see what he would recommend. Maybe some cross blocking will do and wouldn't be that bad.

On the SLC, I agree with you. In hindsight I think that the custom Products guy thought I was also using the SLC as an underlayment and not just a leveling compound.

When you get a chance I would like to hear your thoughts on my staircase questions and the French pattern grout line question.

Since I posted I found a little on the grout line issue on JB but there doesn't seem to be a clear cut solution. My tiles are all exactly 8, 16 and 24" per the pattern. I don't see how having any or all of them trimmed down would help. One poster suggested butting the tiles together and that the resulting gap due to the chipped edge would provide enough of a grout line. He is right about the tiles lining up but I don't know if a shallow grout line would be stable.

Thanks again,

05-18-2015, 03:06 PM
I'm curious why two layers of subfloor would be needed? Ultimately I would think one 1 1/8" layer would be same as 2 layers adding up to 1 1/8 inch? Then I would think you could put down ditra to decouple the tile from the floor to avoid issues with being on wood. Am I missing something?

05-18-2015, 04:23 PM
While there isn't much deflection between joists with a 1-1/8" panel, the ends of the panels sitting on the joist act like a small lever as the open space between gets deflected. Adding a second layer, properly installed (offset joints + other characteristics) protects the ends from projecting through the tile and cracking them. Natural stone has many more imperfections in it than manufactured ceramic tile.

Most SLC's allow you to go to a feather edge over a SLAB, but not over a wooden subfloor. There are a very few that can go to a feather edge over a subfloor, and many of them cannot be used that thick. In fact, most of them want some minimum of 1/2" over the highest point AND require lath to be installed on the floor first.

Unless you add some supports between the large spacing, engineering analysis done previously says what you have does NOT support natural stone installation.

05-18-2015, 09:02 PM
On the stair question, you would definitely need a tile underlayment. Are you doing tile over the treads and risers? What are the treads made of, the same 1 1/8" plywood, or 2x12's...or something else?

Without cutting the tile as needed, your spacing will have to be adjusted to allow for a minimum grout joint in some places, resulting in a somewhat larger grout joint in other places. I would probably cut the tile down where needed to create a grout joint. The significant difference in grout joint size would be something I wouldn't want to look at.

05-18-2015, 09:16 PM
IF the tile are sold specifically for that pattern, they wouldn't be exact multiples of each other! They need to be slightly less to allow for a consistent grout line all around each tile if you don't want the pattern to 'walk' (which typically may not look great).

05-19-2015, 01:57 PM
Kman - I will be removing the original 1 1/8" plywood treads, installing 2 x 12 blocking between and level with the top of the stringers and I can apply underlayment. I was told by one contractor in a casual conversation that the structure is so rigid that I don't really NEED underlayment but it wouldn't hurt to use it, my choice. Since I don't know myself, I was looking for a consensus of opinion on the matter from this forum.

jadnashua - I tried modelling the pattern in SolidWorks and and I reduced the three smallest tiles by 1/8" while leaving them square. It didn't work. Next I'm going to try some asymmetrical cuts and see how that goes. I've done some small areas with the French pattern and I just cheated the grout lines as I went. It looks good but I don't know if I can pull it off in larger areas.

The stair treads will be fabricated from 12 x 24 pavers in a "runner" pattern, i.e. 24" up the center with two shorter pieces on each side. I'm not crazy after all!!

Keep the replies coming I appreciate them all.


05-19-2015, 04:36 PM
No manufacturer of tile underlayment, whether it be a cement board or a membrane, allows for the use of their product over dimensional lumber like you have planned.

Are you planning on removing the existing plywood because of the height issue?

05-19-2015, 06:01 PM
That pattern needs to be properly sized for the grout line used. If you take the nominal tile dimensions, and place them together without grout lines, everything works out. Now, spread them apart to allow for a grout line, and say where an 8x8" tile should fit and end even with the larger tile, it will stick out by the size of the grout joint, well, actually by about 2x the size of the grout joint width chosen. It can get complicated.