I have replaced part of the subfloor that was damaged in my 5x7 bath. In a few places where the original and new subfloor meet there is a little variance in height (no more than an 1/8"). My question is this...can I use thinset with the Hardibacker to make it level enough to lay 12x12 ceramic tile. I don't think self-leveling compound will work due to the gaps in the planks of the old subfloor.
Here's a pic, copy and paste:
http://i18.photobucket.com/albums/b117/jclaar/DSC00852.jpg

 

Its good that you posted this picture. It shows the subfloor is part planking and part plywood. The plywood is good, the planking is not. You cannot put cement board directly over the planking. There is too much movement in the individual planks, and that movement will transfer through the cement board to the tile causing cracking grout and cracked tile. You need to put another layer of 1/2" plywood down before you can put down the cement board.

 

So put another piece of 1/2" over the entire floor? Plus backerboard and tile will be an additional 1" of height from what I have now. That's alot.

 

Yes its alot but its what you need to do. The plywood is an absolute must. You could use noble cis or schluter ditra instead of the cement board over the 1/2" plywood. This would save you some height.

 

Another option that you have if height is an issue is to remove the remaining planking and replace it with 3/4" plywood. You chould then use 1/4" cement board or CIS or ditra over the plywood. I assume you are installing ceramic and not some kind of natural stone. One layer of plywood is ok for ceramic but all natural stone requires two layers of plywood.

 

I think I'll just go with the 1/2" over the whole thing. It's not a bad thing to have the extra strength. The whole bathroom's gutted, so it's getting a new door and everything.

 

Sounds like a good plan. More plywood is always better. Its extra cheap insurance that you wont have future problems.

 

Okay, I have a total of 1-1/4" thick subfloor now in a 5x7 bathroom. Only 5x4.5 feet of the bath will be tiled. The floor slopes slightly from the middle of the floor to the back wall. Maybe 3/8" over 4 foot. I am using 12x12 ceramic. If I choose not to use slc, will I still be okay?

Here's a pic:
http://i18.photobucket.com/albums/b117/jclaar/DSC00863.jpg

 

The floor doesnt have to be level, it just has to be flat. If you can live with it not being level, and it is flat, then you are ok to go. Give some thought to the fact that you'll want your toilet and other fixtures to be level though. Vanitys and tubs can be shimmed no problem. Toilets you can shim a little if they rock, but try to get the area where the toilet will go as level as possible.

 

Yeah, that's the problem...it's not. Take a look:

http://i18.photobucket.com/albums/b117/jclaar/DSC00931.jpg

http://i18.photobucket.com/albums/b117/jclaar/DSC00930.jpg

http://i18.photobucket.com/albums/b117/jclaar/DSC00929.jpg

 

Is that low spot where the closet flange will go.

 

No, the low spot is on the opposite wall of the toilet.

 

From the looks of the pictures you need to do some corrections to the floor before you tile. Going over that hump in the middle of the floor with 12x12 tile that tiles gonna rock. Put down 1/4" cement board over the whole floor. Remember it gets bedded in unmodified thinset using a 1/4" notch trowel. Check again to see how out of plane it is. If its not to bad say less than 1/4" and a small area you could try to screed some thinset in the low area. If its a larger area or more than 1/4" youll have to use slc. Remember all leveling goes on top of the cement board. If you are going to use slc, post back here and Ill direct you to some good slc instructions.

 

Okay, thanks.