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gtimk4 12-20-2010 05:48 PM

Cement backer board over kitchen concrete slab
Hi! All, I have a question regarding the hardie cement backer board apply on concrete slab.

The kitchen that Im working on has concrete slab, Im 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 Im planning to apply thin set over concrete slab, then put hardie backer board over it, then lay down 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. wont 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 dont 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

epson 12-20-2010 10:59 PM

I think the best way to raise the floor is to install a mortar bed but if you want to install the backer board make sure you use a notched trowel and thin set mortar to bond the cement board directly to the concrete. No screws needed.

almazon 02-19-2012 02:46 PM

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.

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