Levelling a curved floor [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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09-21-2005, 10:49 AM
I'm putting marble in a small foyer, and I have issues with the floor. It has a slight rise in the middle, so that the center is about 1/4" higher than the edges. I thought that by putting hardibacker in, and being conservative and aggressive with the mortar beneath, that the rise could be minimized. But the screws did such a good job of pulling down the hardibacker, that the same slight rise is still there.

The subfloor itself is two layers of good plywood. It feels rock solid, with no movement.

I'm not sure what to do at this point. Depending on where I put my tile seams, none of the pieces rock when I lay them on the floor.

This is over a nice dry, ventilated crawlspace, but the joists are not accessible. So I'm wondering about either pulling up some of the hardibacker and putting something under it, or putting a layer of something else over the hardibacker.

Thanks for the help!


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09-21-2005, 10:57 AM
Jeremy, you will be using a medium set mortar to set your marble. It has enough "body" to it that you can level your floor as you go along. You can run level lines across the room for reference points.

If you don't want to try that, you could screed thinset over the floor, or even use self leveling concrete.

09-21-2005, 11:06 AM
Thanks. I'm glad that step one isn't necessarily "rip it all out and level the joists no matter what". I still have the rest of the mortar from under the hardibacker. It is Keraflor dry-set tile and stone mortar. Can this be used to create a level surface? I can imagine making a straight rail that would ride on the high point. 1/4" just doesn't seem like an impossible difference to me.

Also, I was sent home with NA2100 tile and marble adhesive. Is this the medium-set that you mean?


09-21-2005, 05:53 PM
Thanks for your help so far. I think I am going to do a level coat (screed?) of mortar. Its a small enough area that I'm confident in trying that.

I just need to know though: is the Keraflor dry-set tile and stone mortar good for that purpose? And then the tile adhesive goes right on top of that?

Thanks again.


09-21-2005, 06:01 PM
Yeah, but it's best to let your screed dry overnight before thinsetting down your stone,otherwise it'll sink in all that mud. :bow:

09-21-2005, 06:49 PM
If the adhesive you mentioned is in a tub, pre-mixed, take it BACK! You want mortar - the real stuff, to do your floor.

09-25-2005, 07:32 AM
I wanted to provide an update. I now kneel before the altar of thinset. It was amazingly easy to use a 2x4 to drag a level surface about 1/4" deep. It looks great, and its perfect with the tiles dry-laid on top. I also found that in the small high areas that I inadvertantly made, the mortar can easily be scraped away with a putty knife.

For future reference, would it be preferable to do such a screed first, and then backer board on top?

Thanks for the help.


09-25-2005, 08:19 AM
No, do your leveling after the backerboard. Sometimes, the backerboard cancels out any need for minor leveling. You just got lucky.;)

09-25-2005, 08:21 AM
For a slight humps like that in the subfloor, we usually have a framer on the job run a hand-planer over the rise to make it flat. Otherwise, self-leveling compound can be applied to the hardibacker after it's installed.
Best of luck,

09-25-2005, 12:53 PM
May I ask another question? I'm getting less certain of the type of adhesive I should use for the actual marble tile. I can find references to using: special marble and stone adhesive (premixed), latex thin-set mortar, or thin-set mortar (the same I used for the screed). Which is the best for marble?

How small of a notch can my trowel have? I'm worried about too much added height under the front door.

This is starting to look nice. My screed came out really fine as far as I can tell. Is it possible to spray on a little water when levelling to make it easier to work?

I really appreciate all the expertise here. I've gotten a huge amount of info from reading the other threads.


John Bridge
09-25-2005, 02:28 PM
Hi Jeremy, :)

What kind of mud did you use to level out with? Everything you use should start out dry -- to be mixed with water. Nothing should be "pre-mixed."

You can use any thin set to set the marble, so long as it's not the really cheap stuff. $12 a sack and up is fine. Don't by the 4.95 stuff. ;)

09-25-2005, 03:06 PM
I used Keraflor dry-set tile and stone mortar to level. I have a sack of Tec Sturdiflex latex-modified mortar, and another sack of Tec thin-set mortar (and this one WAS $4.95!). Is the latex-modified mortar (c. $12) a good choice to lay the marble with?

I've got it dry-laid right now, and it looks quite level.

Thanks very much.


PS. I accept that pre-mixed is bad. But why is it bad?

John Bridge
09-26-2005, 10:25 AM
yeah, the latex is fine. Through away the 4.95 stuff. :)

10-03-2005, 05:24 PM
I wanted to offer an update to the kind folks here. The screed worked perfectly. I got the marble all cut dry laid, and it looked perfect. I cracked one, so I went to buy another box to replace it and redo one cut. And of course I dropped the box of marble on my toe and broke it. I'm on crutches for six weeks.

So it looks like a professional will be finishing this one.