I have recently replaced the carpet in one room. I intentionally left part of the room uncarpeted that is in front of small vanity. I plan to tile it. Off to the side of the section is a bathroom with a door that is tiled. The bathroom tile is raised, I'm thinking that they previous owners tiled on top of tile. So, when I put down the new tile, I need to try to match the height.

So, I have a few questions.

  1. Should I put down backer board onto the slab? How do I secure it to the slab? Maybe some sort of glue?
  2. How should I handle the seam between the carpet and tile? Remember, the carpet is already down.
  • What type of tile is in the bathroom? What type of tile are you going to lay? Aug 20, 2015 at 14:35

2 Answers 2


I hate to tell you that I know from calling the manufacturers of both hardiebacker and durock that they do no support concrete installations. Both indicated that it would probably work fine but they simply haven't tested it.

I have personally used it in a very small area that I needed to raise - very small. You want to treat it like tile (thinset with large trowel) then hit each sheet with 4+ tapcon screws (which are hard to get just right). This 2'by4' area took me way too long and I am not sure how I could have made it faster. It has held up in a rental for 6-7 years now with no issues.

I would think before doing this. Also I would choose durock since it is a little more flexible than hardie (I prefer hardie for everything except floors).

Given you are raising this area with the carpet, there is simply no logical transition. Normally you would just buy a metal tile transition "L" and lay the flat side towards carpet... This will leave you too high. The only thing that I can think of - and maybe others have ideas) is to basically raise the carpet area towards the tile, basically building a mini ramp. Roofing shingles and plywood will get that job done. Let's be clear, building a ramp so your carpet meets your tile OK is pretty ghetto. It might turn out OK, but you will know.

After all of these workarounds to get everything lined up, that shouldn't be I would have to ask the question - wouldn't you be better off demoing the tile in the bathroom and laying the tile on the slab? Demoing tile isn't that hard and laying tile on a slab is the simplest install. Depending on size of bathroom this may be the least time consuming thing. I know you have a bit more in material cost but this is a permanent solution and the right way.

The crew I flip houses with have a simple motto - we do hard stuff, we do some stuff a bit ghetto, but we never make the ghetto stuff hard.



The size of your new tile will prescribe the size of your trowel. 12" tile usually calls for a quarter inch square notch. That bed of thinset would compress to slightly more than an 1/8". Depending on your troweling skills, you could fudge the height with extra thinset (within specification on the bag) or use a threshold for the transition, as you will also have to do with the carpet.

If the distance is too great or if you'd rather have only a single change of plane at the carpet, I suppose you could embed backerboard with thinset (as if it were a giant tile) but I would seek the advice of the manufacturer first. AFAIK, it's just not done; what if the corners peel up while it sets? What will bed it down? [OMG, why?] -theFloorPro.com

Unless you are experienced with how uncooperative "self leveling compounds" can be, don't even consider using them.

Dealing with Carpet:

You're going to have to protect the carpet very well or pull it back while you work. Over shooting with the tile and cutting the carpet to fit once it's all done would be much easier than cutting tiles. Otherwise you might be SOL on the carpet if you end up with a gap that's to big for a threshold; a lot of extra work for nothing.

-Don't plan your thousand dollar tile around your hundred dollar carpet (that's liable to get messed up in the process anyway).

Just tile the slab and use transitions.

For reference:

How to Tile.

How to Transition.

"Dry Pack" Mortar Beds.

  • For the record, Hardibacker specifically is supposed to be installed over a bed of unmodified thinset. I'm not sure if the other brands of CBUs are the same.
    – William S.
    Mar 22, 2015 at 14:49
  • Mastic?? Unless we are talking vinyl tile here, I think you mean thinset.
    – Ecnerwal
    Mar 22, 2015 at 16:18
  • I've always called thinset mastic. They're decidedly different things?
    – Mazura
    Mar 22, 2015 at 16:53
  • 2
    Yes and if you mix them up .... baaaaad things will happen. Mastic is a type of glue and will soften and return to it's original soupy state if it is wet for long enough. Thinset is a cementious powder that undergoes a chemical change when it cures and hardens. Imagine if your driveway got soft and squishy every time it rained? Not good.
    – William S.
    Mar 22, 2015 at 17:34
  • TFD Mastic: 3. a pasty form of cement used for filling holes in masonry or plaster. I knew I wasn't crazy; but it is indeed not commonly referred to as such. I'd never heard of the resinous mastic tree either. Mastic to me is any of the builder's smutz that adheres stuff; thinset mixed with water becomes a mastic. I can see how this would be a BIG problem -Noted.
    – Mazura
    Mar 22, 2015 at 19:20

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