# self leveling over cement board?



## raslez (Mar 28, 2012)

Hi All, 

I'm planning on installing 12x12 travertine in my bathroom floor. I put durock backer board over the subfloor however when I started dry laying the tile I noticed there is one corner of the board that slopes down (my fault for not catching this before). The rest of the floor is pretty much flat. 

The issue is that the slope is causing one of the tiles to "rock" back and forth when I dry lay it out. Obviously this is not good. I was thinking of using extra thinset to help stabalize this but I believe thinset can shrink after drying and not sure if this is the best solution. 

Another thought is to pour some self leveling compound in the corner sloped area which is only about 24" x 24" to make the corner level and tile over that. The corner is along one of the walls and the shower curb. Does anybody see any issues doing this? 

Thanks in advance, 
Ryan


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## JazMan (Feb 17, 2007)

Ryan,

Using SLC is the way to go. :thumbsup: But remember to prime and self leveling, do not level itself completely. 

A few questions for you. Did you spread thinset mortar under the Durock? I assume you fastened and taped the seams with the special fiberglass tape too. Do you have a double layer of plywood under the Durock? Did you check a joists span chart to verify your joists meet the deflection criteria for natural stone which is much different than that for ceramic tile and basic construction standards?

Jaz


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## raslez (Mar 28, 2012)

Jaz, 

Thanks for the quick response. 

I did spread thinset under the Durick and screwed it in. I also taped the seams with the gray fiberglass tape and put a thin coat of thinset on the seam. The bathroom is small (~25sq ft.) so I only needed 2 boards. 

I did talk to the guy at the tile shop in detail about installing the travertine and he didn't mention adding another layer of plywood so i did not do that...However he did recommend the platinum pro flex thinset which supposedly handles the flex/deflection for natural stone? 

What do you think? I guess it's not too late to tear it up at this point. I would really only be out a couple of durock boards and have to buy 2 new ones. 

Thanks
Ryan


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## Amateuralex (Mar 17, 2012)

I had good luck using the Tile Shop's house brand of SLC and primer over cement board. I think the Tile Shop's version has more work time than what HD etc sells. I used a squeegy on a pole to push it around. You really want to do that, it won't get ultra level on its own. The top of it will be flat, but it won't necessary flow ultra quickly into the lowest areas.

I hope someone will correct me if I am wrong, but a height difference of 1/16 could be handled by thinset either before or during the installation of the tile. SLC needs 1/8 or more to really work its SLC magic, cause the high surface tension will prevent it from moving around much when super thin.

I installed travertine in my entryway and only later learned about the requirements for enhanced subfloor for natural stone. It's too late now, so I guess I just have to hope that it holds up over time. I also got the high end thinset and mortar so hopefully it will help.


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## JazMan (Feb 17, 2007)

It is my experience that most salespeople would rather sell you stuff and not necessarily make sure the work is done right. After all, the project will not necessarily fail if done wrong, not every time at least. 

You've got several issues. 

1. The joists may have too much deflection for natural stone. I'd bet on it.

2. You do not have enough plywood and therefore also have too much deflection between the joists. I guarantee it.

3. The floor is not flat, which is an even bigger issue with natural stone tiles.

Let us know; the type and size of the joists, species and grade, if at all possible, the on-center spacing of the joists, and the unsupported span of the joists down to the inch. The type and thickness of the subfloor. The age and overall condition as viewed from below. Approximately where you're located.

Jaz


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## Amateuralex (Mar 17, 2012)

I've learned more reading Jazman's posts on this forum in the last two weeks than all my other research combined. Thanks for the expert information Jazman.


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