Tiling over UFH - large area

[richo106]

Hi

 

We are having UFH throughout are downstairs and planning on tiling the whole area. (120m2)

 

Can I tile directly onto the liquid screed or do I need anything on there to help with expansion etc

 

There is 4 rooms downstairs and will be on different zones heating wise, do the rooms need any kind of expansion gaps between the tiles incase they are different temperatures for any reason?

 

Many Thanks 

[Adsibob]

I hope you don’t need anything in between screed and tile, because we haven’t! 
i think people only use ditra Matt when they are worried there might still be movement in the screed. If your screed has fully cured, and you’ve done the UFH heating cycle recommended by your screed manufacturer, then I don’t think you need ditra.

Edited January 31, 2022 by Adsibob

[joe90]

41 minutes ago, Adsibob said:

hope you don’t need anything in between screed and tile, because we haven’t! 

Nor did I , just loads of primer.

 

47 minutes ago, richo106 said:

do the rooms need any kind of expansion gaps between the tiles incase they are different temperatures for any reason?

I left a gap in the tiles across doorways which is where cracking can occur (note to self, must get round to put mastic in these gaps ?).

[Adsibob]

1 minute ago, joe90 said:

Nor did I , just loads of primer.

We didn't even use primer, what's that for? We've only tiled about 20% of the area we are tiling though, so still time for the rest of it to be primed if necessary. But my screed must be pretty dry by now. It was poured 113 days ago and is 75mm to 80mm thick. I think we have another week or so before we do any more tiling. Should we prime it? 

[Pocster]

My ufh screed cracked months later across the doorways . I have used ditra matting - just so I sleep better at night ??

[joe90]

45 minutes ago, Adsibob said:

We didn't even use primer, what's that for?

It was @Nickfromwales that suggested it.

[Adsibob]

I thought it was only anhydrite screeds that needed priming. Anyway, our tiled floor in the utility room has been down on our sand and cement screed for about 2 weeks and so far no problems. But now this thread has me worried. Though surely my builder knows what he's doing. He's been using the same screed company for a few years and I can't be the first one that has asked him to tile it.

[Temp]

If you don't have expansion gaps in screed at doorways I would use some sort of isolation mat before tiling. It's not enough just to have a gap in the tiles because any crack in the screed most likely won't be straight, it can curve into one room or the other. 

 

 

[saveasteading]

The screed should have done all its shrinking in a month, and there will be multiple cracks, perhaps invisible. Across doors will have cracks and it is fairly likely tiles may crack there later. So i would either fit a strip at each door or keep tiles in case any replacement needed.

Looks great if whole tiles run through. Looks awful if they crack.

[Mike]

7 hours ago, richo106 said:

Can I tile directly onto the liquid screed

If it's anhydrite, then yes, well sealed after it's dried. In other cases check the technical information for your particular screed.

 

7 hours ago, richo106 said:

do the rooms need any kind of expansion gaps between the tiles

Yes, at least 6mm wide at room edges and doorways. If you have large rooms then divide them into bays of no more than 40m², with a maximum length of 8m per side.

 

I also choose a 'flexible' adhesive - rated S1 or (better) S2 - suitable for the tile type and size. Your supplier will be able to advise you.