tiling over two diffrent subtrates

[jonnyc]

I am quoting for a job where part of floor will be new screed with water underfloor heating pipes under screed over insulation and other part same water underfloor heat pipes laid between joists and surrounded by screed between the joists.
finished terracotta floor needs to be flush over whole area .
I cannot think of any over subfloor prep that wher i could guarantee tiles would not crack where they bridge two substrates .

any ideas welcome

 

[beanz]

I'm not sure you can guarantee that, without expansion joint where the two floors meet.. Can you lay cement board without mechanical fixings? Just flexi rapid.. Then put Ditra on top? If that's possible, it should give you a few extra mm for expansion.

I'll watch this thread with interest, as it would be good to have a conclusive answer.

 

[Chalker]

Two different floors, with different expansion rates. The timber will expand more and quicker. Then you have the terracotta, not the strongest thing in the world. I would decouple both rooms and separate them with an expansion strip or at least a cut along the joint.
Glad I'm not doing it! Will also read this thread with interest and see how it pan out.

 

[Brian the Tile]

Fill it with Silicon, sorry

 

[jonnyc]

I'm not sure you can guarantee that, without expansion joint where the two floors meet.. Can you lay cement board without mechanical fixings? Just flexi rapid.. Then put Ditra on top? If that's possible, it should give you a few extra mm for expansion.

I'll watch this thread with interest, as it would be good to have a conclusive answer.

well thats a point i brought up with hardie. the new hardie floor is definitely not gauranteed unless screwed and glued to joists so you could not have screed flush with top of joist and then simply ovelay hardi floor 19 or 22 mm bridging join and glue hardie floor to screed with cement based adhesive.
so one could think of the option of 18mm min plywood glued and screwed over joists.
no problem fixing 6mm hardie backer board fixed with flex adhesive and screwed in to joists, but same problem when you get to the screed part .
you can fix 6mm hardiebacker with flex adhesive to screed but this is not guaranteed.
is the fact that you cant screw fix in to screed really that important !

 

[beanz]

well thats a point i brought up with hardie. the new hardie floor is definitely not gauranteed unless screwed and glued to joists so you could not have screed flush with top of joist and then simply ovelay hardi floor 19 or 22 mm bridging join and glue hardie floor to screed with cement based adhesive.
so one could think of the option of 18mm min plywood glued and screwed over joists.
no problem fixing 6mm hardie backer board fixed with flex adhesive and screwed in to joists, but same problem when you get to the screed part .
you can fix 6mm hardiebacker with flex adhesive to screed but this is not guaranteed.
is the fact that you cant screw fix in to screed really that important !

have you looked at any other boards? I thought there were some that didn't require screwing.. Marmox maybe?

 

[jonnyc]

Two different floors, with different expansion rates. The timber will expand more and quicker. Then you have the terracotta, not the strongest thing in the world. I would decouple both rooms and separate them with an expansion strip or at least a cut along the joint.
Glad I'm not doing it! Will also read this thread with interest and see how it pan out.

this is the most sensible option with expansion joint but the tiles are a weird shape and would look rubbish.
but at least you could use ditra over screed within few days whereby using backer board you should be waiting 8-9 weeks before overboarding.
I have had this scenario manys times and wont reveal yet what i suggest but it is never gauranteed.but i always feel that provided you point out what is right and wrong and client fully understands the risk they are taking and you have disclaimer there are options available that usually work if right prep done . i see so many tilers on this forum that say no to anything that is not technically correct and must lose so much work.
when we lay reclaimed floors the rule book is out the window virtually every time but i have suceeded with with minimal failures and no guarantees

 

[jonnyc]

if you use marmox over water fed or electric heating you will be stopping heat coming up !!!!!!!

 

[Chalker]

Could you overlay the timber look with 22 mm fermacell ( this floats)

 

[beanz]

if you use marmox over water fed or electric heating you will be stopping heat coming up !!!!!!!

Valid point lol!

 

[Freeze]

John, had a similar job 4 years ago up in Derwent Bay, 185m2 floor of which 110m2 were on to a new screed with UFH. When we arrived we were shocked at the size of some of the settlement cracks, and the levels, 35mm out in places, to cut along story short, we overboarded with. 12mm hardi backer, plugged and screwed, with a two part flexi, leveled with a 50mm fibre based screed, then ditra.
At the time Hardi had never heard of anyone doing this, and when I posted it on another forum it was met with a few oohs and ahhhs, that floor is perfect, not one crack, Jaipur grand opus.

 

[Freeze]

Just to clarify, when I said screed, we used an Slc that went up to 50mm in one hit, researched it and got the one with the highest newton strength we could find

 

[afright]

I will be doing a 100m2 balcony end of next month screeded floor to ply floor so I will be using ditra overall then Schluter movement joint profiles between the two substrates.

 

[beanz]

John, had a similar job 4 years ago up in Derwent Bay, 185m2 floor of which 110m2 were on to a new screed with UFH. When we arrived we were shocked at the size of some of the settlement cracks, and the levels, 35mm out in places, to cut along story short, we overboarded with. 12mm hardi backer, plugged and screwed, with a two part flexi, leveled with a 50mm fibre based screed, then ditra.
At the time Hardi had never heard of anyone doing this, and when I posted it on another forum it was met with a few oohs and ahhhs, that floor is perfect, not one crack, Jaipur grand opus.

How did you avoid the pipes?

 

[Freeze]

They were buried in the screed 65mm so just used a 40 mm fixing