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 silicone, 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

 

[beanz]

Just curious, but what's the purpose of the Hardy in this situation!?!

 

[Freeze]

We originally refused to tile because of some of the settlement cracks, and the levels, this was a 4 million £ house, with a half million refurb, ripping up the screed and underfloor heating and doing it again was out of the question at this stage, after two days of discussions with the main contractor, architect, screed suppliers etc, we were asked how we could move forward and start tiling, we decided that the best way was to bridge the settlement cracks with 12mm hardi, we didn't think 6mm would be man enough, we then levelled the floor with a SCL which could go up to 50mm, then ditra matted, out method of thinking was we were decoupling from the screed in effect twice, like Johnny said, sometimes you can't put a garuntee on your work which we were not prepared to do, the screed suppliers and underfloor heating company covered all our material and labour costs, and the main contractor out in writing to every one concerned that he would take sole responsibility if their were any issues with the tiling

 

[Freeze]

John, sorry to high jack your thread mate

 

[beanz]

I think if you fix mechanically, you aren't decoupling, as the hardy will have to go with the screed. Maybe the hardy screwed either side of the cracks would add some structural integrity though... I must admit, I wonder if the fibre reinforced SCL and the Ditra would be enough to do the job, but wouldn't like to be the Guinee pig in this situation.

 

[beanz]

I hope John doesn't see this as hijacking... Just discussing the problem!?!

 

[Freeze]

I did this job 4 years ago, and like I said their is not so much as one crack (which does surprise me) at the time I spoke to every technical department and their dog, off the record most could understand my method of thinking, and their would have to be some severe horizontal movement for a crack to transfer through 12mm hardi backer, fixed and glued with a two part, levelled with a flexi slc, covered in ditra, with a 20mm stone fixed. Out of interest how would you have tackled it, bearing in mind some of the cracks were 8 - 12mm

- - - Updated - - -

Horizontal and vertical movement

 

[beanz]

I did this job 4 years ago, and like I said their is not so much as one crack (which does surprise me) at the time I spoke to every technical department and their dog, off the record most could understand my method of thinking, and their would have to be some severe horizontal movement for a crack to transfer through 12mm hardi backer, fixed and glued with a two part, levelled with a flexi slc, covered in ditra, with a 20mm stone fixed. Out of interest how would you have tackled it, bearing in mind some of the cracks were 8 - 12mm

- - - Updated - - -

Horizontal and vertical movement

i have no idea, which is why I asked. I'm not having a dig or anything!?! If I don't understand something, I ask. The only time I've tiled over two different substrates, there was no heating involved, so I just SLC'd, and used Ditra. The added heating, and the fact that the slab is new, would make me nervous, so I'm here to learn how to tackle it.

 

[Freeze]

Sorry mate, I didn't think you were having a dig, I felt that due to the state of the screed, that just putting ditra over the top would have had little effect, by bridging the cracks with 12mm hardi we though that would give it the best chance of cracks not transferring through the tile, and in this case we were proofed right, but it was very much a guessing game at the time, and other than rip it up and start again no one came forward with any other solution

 

[jonnyc]

Sorry been caught up with a nightmare marble job .

Have briefly read posts and great that we are discussing options that may not be guaranteed,
for me in my tiling life I have had to take on many jobs that i could not guarantee and I am careful to point out in writing what is considered correct .but they have proved successfull because a considered amount of thought process and experience has gone in to my proposal.darren has given an example of a job he did which was also not the guaranteed and it seems to have worked .
my feeling is that potentially you can be so bogged down by what is right by whose standards ? That one could be missing out on a lot of work and very interesting work .
i know I am self taught but I have managed to survive 28 odd years with 3-6odd tilers on the go and 90 percent of the most amazing jobs I have taken on would be condemned by the the tile association.

 

[jonnyc]

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.

Darren do you think that fixing hardie over screed first, latex on top ,then ditra would be preferable to latex on screed ,hardie then ditra.
i honestly don't know my self .
I think you and I must be giving these Dutch tech boys some sleepless nights.
i am always been told by them that no one has ever asked the questions I ask before !,,but I am sure you are are asking similar