Hearth tile build level issues

[1970gto]

I am installing a brand new wood stove and building a hearth. I have never done tile before so the whole thing is a learning experience for me. Any help would be appreciated.

I removed the carpet and padding. Built a frame out of 2x4 screwed into the floor and sill boards. I then put 3/4 osb exterior over the frame. My plan was to use modified thinset mortar between the osb and harde cement board with a 1/4 square trowel per harde. Then tape seams and use same modified thinset mortar with 1/2 x1/2 square trowel to lay true porcelain 6x24 porcelain tile with 3/16 space. Followed by unsanded grout.

So currently frame is built and osb installed and I checked level. And in a 4 ft run ( hearth is 5'x5') I have a 3/8 drop to the edge of the hearth.

Questions
How do I level this out to prevent problems in the future.

Should I use self leveler over the entire hearth

Can I build a temporary perimeter to hold back the self leveler that I can remove after it dries on the edge and not damage leveler.

Will modified thinset mortar adhere to the self leveler for cement board installation.

Any suggestions on how to remedy this problem would be greatly appreciated. I want to do this correctly if anything I plan to do is wrong please tell me

[cx]

Welcome, John.

Much will depend upon the particular wood-burning appliance you've got, but the stove should have some specific installation instructions for clearance from other surfaces, including the floor, and for the construction of the fire-proof surface of the floor under the appliance. A layer of CBU and tile is not always sufficient.

The suitability of the nominal 3/4" OSB will depend upon the spacing of your 2x4 joists, which we'll presume are installed over an already sufficient floor structure.

Originally Posted by John

Built a frame out of 2x4 screwed into the floor and sill boards.

Not sure what you might mean by "sill boards" there.

By "harde" I'm guessing you mean Hardiebacker Fiber/Cement board, yes? If so, you don't require a modified thinset mortar to bed the panels over the OSB, but you can use a modified mortar if you want. The mechanical fastening schedule is important.

Your tile installation does not need the floor to be level, only flat. The stove might require the floor to be more level than you currently have, or not. The best way by far to correct the out-of-level situation would be to do it at the framing level, and I would certainly recommend you do that rather than trying to level on top of what you've just built.

But by far the most important thing I think you should do is ensure what you're building meets all the requirements of the NFPA for the installation of that stove.

My opinion; worth price charged.

[1970gto]

The hearth is being built to manufacture specs which only requires ember protection. Yes I am using hardiebacker cement board. As far as level that I am talking about. When taking a 4 ft level at multiple different angles and checking for high amd low spots most of it is pretty flat within a 1/16 or less. Except for the outside edge which drops 3/8 of a inch over a 4 ft run. As far as level looking at the bubble it is on the money.. the frame was built over existing subfloor. It is just the one area leading to the edge that drops off low. I was hoping not to tear it back apart and to be able to use self leveler to fix the low area. But if that's what I have to do then so be it

[cx]

What size tiles do you intend to use?

[1970gto]

True porcelain Co. 6x24 porcelain wood look tile

[1970gto]

I attached the frame directly to the existing sub floor. So the low spot in the existing sub floor is being mirrored in the hearth frame

[cx]

And it's at that level where I think you should have corrected the problem, John. And I think it's likely still the best bet, but without photos it's difficult to determine that from out here.

The ceramic industry standard for flatness of substrate for tiles that size is no deviation from intended plane of more than 1/8th" in ten feet nor 1/16th" in two feet. That's what you should be basing your actions upon at this point.

My opinion; worth price charged.

[1970gto]

So would the way to correct the problem be to go back down to subfloor.. put self leveler down to Leven intended hearth area and then my 2x4 frame on top of the leveler. I know I can't screw unto the self leveler

[ss3964spd]

Couldn't you just use some shims between the hearth framing and the existing subfloor, John?

[Carbidetooth]

If the gaps that shims create isn't acceptable, you could scribe the bottom of your frame to correct for slope. Essentially parrallel slope on the bottom and level on the top. Use shims to get level, mark the frame and then cut.

Good example might be when installing base cabinet frames to sloping floor such as garage. When remodeling level and laser is frequently used early on to get a "lay of the land".

[1970gto]

I think what I'm going to do is shim the frame after I Build a couple of support peirs under the house. Then go down with osb, cement board, self leveler and then tile.