Tile hearth level issues

[70gto]

I am installing a brand new pe super le wood stove and building a hearth. Stove only requires ember protection. 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 hardie cement board with a 1/4 square trowel per hardie. 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 sanded 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. The rest of the hearth is level as far as no gaps between the level and the osb when checking in multiple angles. And that part of the hearth is also level when looking at the bubble. But the one side of the hearth drops 3/8 in 4 foot run compared to the rest 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

 

[begreen]

Has the OSB already been nailed to the frame? If not, the best way to address this is to shim the frame to level in that corner. Then, all will be level going forward. This is assuming that there is a low spot in the floor and not a bowed 2x4. Have you checked the floor level in this area? If the floor is off, does it need support underneath?

There is no need to use thinset between the cement board and the underlayment. Screw down the cementboard per the mfg. guidelines. For Durock I think that is something like a screw every 8". It definitely is not going anywhere.

 

[70gto]

The osb is screwed down. So I can pull it back up and shim it. No I did not check the floor originally for low spots. But I'm pretty sure the low area on the hearth is caused by sub floor. So if I shim it get it up the best I can. Then I can do final level with self leveler