Very large format porcelain, partial anhydrate screed UFH

[lbstyling]

Forgive me for I am noob...

I have a 9m x 9m floor area that is one space, but half is a new build extension and half is 1920's old house

Situation:
The new build half has a Anhydrite screed floor with UFH.
The old half is concrete floor WITHOUT UFH.
The tiles are 1200mm x 600mm porcelain.
The surfaces are not quite level (old house floor is 20mm lower) but finished surface needs to be continuous level floor

Actions so far:
-Screed was laid last year
-I have sanded back the laitance on the Anhydrite screed (not that there seamed to be much to sand??)
-UFH has been running for 3 days with no cracking.

Current thinking/plans:

-SBR mixed 1:1 with 2 coats on the floor at 90 degrees to each other on new anhydrite floor.
-Anyhyfix tile adhesive on the Anhydrite floor (I would like a slow setting alternative if there is one?)
-Mapai Keraquick/latex plus on old floor (is there a cheaper slow setting alternative that is good? Do I need the latex plus?)
-'Backbutter' the tiles
-3mm tile spacers
-Foam and Silicon expansion joints every 3 tiles or so?
-Foam and Silicon expansion joint all along where the old concrete floor meets the new anhydrite screed.
-Not sure how to best raise the old house floor 20mm. I was thinking of using a decoupling mat on the old house, or perhaps use self leveling compound and put a electric UFH mat in there too?

Any advice appreciated. I have done a little tiling before, but this is way past that!

Thanks.

 

[Adamskionline]

You're not far off with most off your thoughts here.

I'd consider a decoupling mat everywhere, but dont bridge the substrates with it. Expansion joints are key. No need to foam, just use a Silicon to match the grout and it'll do the same job. If you can use a thin profile manufactured expansion joint for where the substrates meet you'll stand a better chance of no cracking in the long term.
you can easily build up 20mm using a tile backer board which will also give you a good thermal return on your new ufh.

Good luck with it

 

[lbstyling]

You're not far off with most off your thoughts here.

I'd consider a decoupling mat everywhere, but dont bridge the substrates with it. Expansion joints are key. No need to foam, just use a Silicon to match the grout and it'll do the same job. If you can use a thin profile manufactured expansion joint for where the substrates meet you'll stand a better chance of no cracking in the long term.
you can easily build up 20mm using a tile backer board which will also give you a good thermal return on your new ufh.

Good luck with it

Thank you so much for your reply!

To keep all up to date:

I have purchased Mapai keraquick for use thoughout with the latex additive that's makes it a super sticky S2+ spec.

I don't plan to use a mat now as the Mapai will have circa 10mm compliance in movement, this is much more than the anhyfix stuff, and the mat is expensive.
I will leave 10mm + gaps around the whole floor, and put a lot of expansion gaps in, perhaps all of them!

At the moment, for the height difference, I'm thinking self leveller, as it will be level, I can put the electric UFH mat in it, and the tiles are huge. Haven't researched this much yet, so may change.

 

[lbstyling]

While I'm here, I have another tiling job I'm doing outside. I am using the same porcelain tiles on the garden walls.
The walls are concrete block, but the height is uneven by about 30mm total.
What should I use to level the top before tiling? Just mortar? Any prep advice?

Thanks all.

 

[Adamskionline]

Sand and cement will do it, use a bit of sbr on the concrete blocks before you put the mix ono get a good bond.

 

[lbstyling]

Thanks bud!

Sand and cement will do it, use a bit of sbr on the concrete blocks before you put the mix ono get a good bond.

Thanks!

Starting this tomorrow then!

Update: I changed my mind on the ditra mat and have bought a similar product, but one that has space for a electric heating element.

Dural Durabase CI-FH Decoupling Mat - 15 SQM - Element Shop

Dural Durabase 15sqm CI-FH is a decoupling matting that doubles as a carrier for electric underfloor heating cables.

www.elementshop.co.uk

I couldn't live with the idea that if the floor failed it could have been down to my saving a bit + it makes laying the heating element much easier.

I have now abandoned the idea of self levelling compound to get the 20mm needed height due to cost.

By have 2 more questions:
1) is it ok to use thermal backing board like this-

ProWarm BACKER-PRO Tile Insulation Backer Board - 1200 x 600 x 6mm | Wickes.co.uk

ProWarm BACKER-PRO Tile Insulation Backer Board - 1200 x 600 x 6mm

www.wickes.co.uk

instead of 'hardibacker' or similar and

2) what is the best way to attach the boards to the floor- screw or adhesive?

Thanks!

 

[lbstyling]

P.s:
When you say don't bridge the 2 different substrates with the ditramat, I thought that was the point of it? Can you explain?

Apologies for all the questions: PM me your address and I will send you a bottle of somthing for all this!

 

[Huddersfield Tiling]

Not suitable to tile. Think of another flooring.

 

[parkerfresh]

Not suitable? Please explain.

 

[Ajax123]

You have a physical break between the two substrates which should reflect through the time face. This constitutes a movement joint. Ditra is to stabilise unstable screeds and should not be used to bridge movement joints. If you do the differential movement both horizontal and vertical will likely break your tiles and they’ll crack and start to fail.