Discuss Very large format porcelain, partial anhydrate screed UFH in the UK Tiling Forum | Tile Advice Forum area at TilersForums.com

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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 silicone expansion joints every 3 tiles or so?
-Foam and silicone 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.
 
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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 silicone 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
 
OP
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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 silicone 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.
 
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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.
 
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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.


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-

instead of 'hardibacker' or similar and

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

Thanks!
 
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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!
 
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