First time tiler needs advice!!

[Daver77]

Hi all,
Iam new to this forum and have already found a lot of helpful info, but are in need of some specific advice.
I am gearing up to install 1/4" 13"x13" porcelain tile on my fireplace hearth that I had to enlarge to meet code (now 65"x30"). I removed the existing brick hearth to find a bunch a rubble that once removed back to a solid layer left me about an inch below the subfloor. I used SLC to bring it back up to the subfloor but then unfortunately discovered a drop of 1/4" over the 30". To fix this drop I towelled on thin-set and are now back at the subfloor level although i do not have a perfectly flat surface.
My question is:
Should I do another layer of thinset to build up the entire area 3/16 or so (to allow bedding layer to bring me flush with the finished floor) or should i use a medium bed or dry bed mortar and go with what I currently have??
Any advice would be much appreciated!!
Cheers,
Dave

[Daver77]

I thought a couple of pics might help (althought the lighting tonight is terrible)

[koihito]

Hi Dave

I will assume you want to end up flush with your hardwood and that the hardwood is 3/4". Were I you under the tile I would use:

1/4" CBU and use extra thin set to make up the difference in the low spot and then cover that with a liquid crack membrane.
or
Schluter Ditra XL.

Technically the CBU is not meant to be thin set only (witch you would be doing over the old hearth area) so the Dirta would be more correct. Either way you do run a risk of problems with the cold joint between the the ply and old hearth. It will probably be O.K. But I would not guarantee such a job.

[Houston Remodeler]

Most thinsets are engineered to be thin. The upper limit being 1/4" total thickness.

You'll want to switch to a medium set when crossing over the magic 1/4" line

[Davy]

Dave, if it's under 1/4 inch, continue to build it up with thinset and a straight edge. Use a rubstone to knock the high spots off once the thinset dries. Once you do that, check it with a straight edge again. It may need another application. Sweep or vacuum it and then wipe it with a wet sponge to get the dust up.