Porcelane tiles on concrete floor, does it need Ditra Matic?

[silverfoxmentor]

We are in the middle of a refurb and have a concrete kitchen floor with under floor heating which we are planning to lay porcelain tiles onto. We have just been told that we will need to lay Ditra matic under the tiles.

Given concrete is pretty solid and the additional cost for laying Ditra Matic is substantial, is it really necessary?

 

[tpt]

Few questions:

1. How long has the concrete been down ?
2. Was it a pumped screed, or was it a normal sand\cement one?
3. Is it electric or piped (water) underfloor heating?
4. What is the area?
5. Are there any expansion joints in the screed? (if its a small area, prob not)

Ditra matting is all about absorbing lateral movement (expansion\contraction) and it may also be used to seperate the layers. answer the above and i should be able to give you more info

 

[silverfoxmentor]

Picking up the points you made

1. How long has the concrete been down ?

A few weeks for some of it, rest 25 years, sectioned off by room rather than within room

2. Was it a pumped screed, or was it a normal sand\cement one?

The recent concrete came made up in a mixer if that is helpful and was laid with wheelbarrows from the mixer

3. Is it electric or piped (water) underfloor heating?
Piped

4. What is the area?
140 sq metres

5. Are there any expansion joints in the screed? (if its a small area, prob not)
Not sure will find out. The screed does join old screed in 4 places as it changes rooms
Read more: //www.diynot.com/forums/tiling...eed-ditra-matic.386160/#2965484#ixzz2n15uL4Vw

 

[silverfoxmentor]

.....and many thanks for taking an interest, I am a novice at this

 

[tpt]

ok, they may be suggesting ditra due to the age of the new concrete, but its more likely they are suggesting it as a decoupling membrane to stop cracks where the old screen meets the new screed. because the old screed isn't heated, and because its older it will behave differently to the new screed. because of this you may get cracks and the joints between the slabs. Ditra will solve this, but its quite expensive from both a material and a labour point of view.

Depending on the size of the each room, and the placement of the joins (i.e. are the joins all in the doorways, and are the rooms all -err...room size ) you might be able to skip the ditra and put a break into the tiling using a threshold strip - but i'm assuming you have asked for it all to be tiled continuously is that right?

one final thing, what is the material you are laying?

Your tiler is giving you good advice, but it may also be due to what you are asking for. may be worth asking them the reason they think you need ditra

 

[silverfoxmentor]

Thanks again for this. We are having under floor heating on all the concrete, new and old and you are correct that we do not want a break in the tiling. Your suggestion that the vulnerability is between the old and new concrete feels right, but the additional cost is very significant (and a surprise), so I am trying to find out why the builders tiler is saying we need it, for sure.

Is there a way we could just use it along the jointed area, or will that lead to different levels

 

[tpt]

yes its all or nothing. Your tiler is right if you have UFH over varying types of screeds and a continuous installation.

Yes it will increase the levels a lot - around 10mm, and yes its expensive. You'll also use double the adhesive as you fix the ditra down, then tile on top.

I'm curious about how you are getting piped UFH into the old screed - is it being overscreeded?

There are other types of matting, durabase for instance and the cost is quit a bit different. search for uncoupling membranes

 

[silverfoxmentor]

We are digging it up and relaying it deep enough for the underfloor heating to be laid and then reconcreting/screeding on top. So, I guess it is better to say that the top layer of concrete and screed will be consistent across the whole area, but the hard core base of some of it will be 25 years old