I am looking for some clarification and any help would be greatly appreciated. We are do - it - yourselfers and have done lots of tiling in the past but never installed a heated system under the tiles so my questions are:

1. Between the wooden subfloor and the tile backer board that we have put down we have 1 1/2" of flooring and now ready to install the heating cable. Should we use thin set mortar or self leveling to embed the cable? (Or floor is pretty straitght and level) After reading lots on this site should be be worried about the thin set crumbling under the tile?

2. Should we put ditra over the heating system? If so can that be set using the morter to embed the cables or does it need an additional layer? (We are worried about the height difference going to the living room carpet)

Thanks is advance for any advice that could be given.

Just to clarify your subfloor, do you have two layers of plywood plus a tile backer?

As far as the tile backer is concerned, it was not necessary when you are installing a wire heating system. Is the tile backer installed with thinset under it and fastened every 8" OC?

I would highly recommend using Ditra over the heating wire.

You can use a modified thinset over the heating cables or self levelling cement. If you use the SLC then an uncoupling membrane like Ditra should definitely be used.

DO NOT let anyone convince you to use a cheap scratch mortar to cover the heating wire! It will fail!

I don't know what your skill level is so the choice between an SLC or thinset to cover the wires is going to be up to you. Thinset is much harder to do when covering the wire, especially if you do plan on using the Ditra. Ditra needs a really smooth and flat underlayment to achieve a proper bond.

Yes, We have two layers of plywood plus the tile backer.

Thanks for all the GREAT info.

One thing that we were considering because the self leveling cement is pretty expensive was to get a thin tile backer and putting that under where the cabinets, stove and fridge go then just putting the SLC over the wire. Would that be a good idea?

OOPS I forgot to answer the question. The tile backer is fastened every 8" OC.

But, does it have thinset under it?



If your going to tile those areas,then my answer would be no.
A minimum tile backer of 1/4" plus thinset is going to higher than the wire with an SLC or thinset skim coat. Both those products are only set to the top of the wire. It only needs to be flat enough over the wire to be able to install the Ditra properly.

I have done about 50 installs of tile directly on heating cables leveled with thinset. So far no callbacks. That does not mean that ditra is not better, just that it is not necessary.

When installing cables I use only staples (not the plastic strips) I find this saves me about 1/8 inch in floor thickness and a lot of thinset. I also recess the probe and cable splices into the floor. I use the cables as screeds for a 16 inch trowel and embed them with ralatively stiff thinset. Then the next morning while it's still relatively soft I go and sand off any bumps and ridges.

Good post. I appreciate it! Thanks for guiding.