Cement backer board over kitchen concrete slab
 

Hi! All, I have a question regarding the ½” hardie cement backer board apply on concrete slab.

The kitchen that I’m working on has concrete slab, I’m putting a 3/8” porcelain tile in the kitchen floor. I want to raise the floor as much as possible to match the adjacent living room floor level (about 1-1/8”).

So I’m planning to apply ¼” thin set over concrete slab, then put ½” hardie backer board over it, then lay down ¼” thin set on top, and put the 3/8” porcelain tile at last. (the whole assembly may not be 1-1/8” but close enough for me)

I know that hardie manuf. won’t warranty their product if it applies on the concrete slab directly. I also know that many people in the forum points out that I should not do it either. Here are my questions:

1) If I don’t care about the factory warrant, do you guys think that it is OK to use hardie backer board over concrete? If not, why?
2) How do I secure the board to the slab, would thinset be enough, or do I need to put additional screws to the slab?
3) What screw should I use?
4) What is the better way to raise the floor other than using backer board? I try not to use self-leveling concrete or similar method since it is too difficult for me to do. Do you guys have other recommendation?


Thanks a lot for your help

I am doing almost same project right now.

I am working on 1/2 bathroom on the 1st floor. Its about 27 sq ft. I removed old tiles already with hammer and pry-bar. I damaged mud bed under the tiles though, so I had to remove it too.

So now I guess I have to chose between SLC or Mortar Bed since I had Total Fiasco with CBU over Concrete Slab. Its like glueing two pieces of metal with Crazy Glue.