tiling over two diffrent subtrates

[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

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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

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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

 

[Freeze]

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

To be totally honest John Im not sure, the only reason we went Hardi first is that we wanted to bridge the biggest cracks in the middle of the boards, so by not levelling first the cracks were visible, didn't want the cracks on or close to the edges......you have got me thinking now whether it was best that way.

 

[jonnyc]

To be totally honest John Im not sure, the only reason we went Hardi first is that we wanted to bridge the biggest cracks in the middle of the boards, so by not levelling first the cracks were visible, didn't want the cracks on or close to the edges......you have got me thinking now whether it was best that way.

Darren I don't know myself but I can see the logic why you chose your route if you wanted to bridge the cracks in middle of boards as best possible.so there is a logic in our method of madness.i was thinking if slc down first then no danger of piercing pipes when screw fix boards if any pipes floated up .
but just goes to prove my theory that a considered methodology is one well worth looking in to.
how many tilers consider where they they start a run of insulation boards and where those joints will be in relation to ply board joints underneath

 

[TJ Smiler]

I have never screwed into SLC (Situation has never arose where i have needed too) although i know it's solid i get the feeling it it wouldn't grab a a screw (or plug) so well............... Not quiet sure why i feel that but it's just floating in me guts i guess. I think if i were in the same situation as you at the time i would have gone with the Hardi first on SPF and screwed then SLC on top too. Hmmm food for thought though.

I have also on a few occasions where i have had to go over two different substrates (where customer was adamant they don't want an expansion joint) set the floor out so i get a grout joint right on top of where the two floors meet and then opened up that one grout joint by a mm or 2 and then siliconed it with a matching color to the grout. I did one of these in August 2011 and have been back several times to do other works in their house and it is still in perfect condition.

 

[beanz]

I have never screwed into SLC (Situation has never arose where i have needed too) although i know it's solid i get the feeling it it wouldn't grab a a screw (or plug) so well............... Not quiet sure why i feel that but it's just floating in me guts i guess. I think if i were in the same situation as you at the time i would have gone with the Hardi first on SPF and screwed then SLC on top too. Hmmm food for thought though.

I have also on a few occasions where i have had to go over two different substrates (where customer was adamant they don't want an expansion joint) set the floor out so i get a grout joint right on top of where the two floors meet and then opened up that one grout joint by a mm or 2 and then siliconed it with a matching color to the grout. I did one of these in August 2011 and have been back several times to do other works in their house and it is still in perfect condition.

I think we'd all prefer to do it this way, but 9 times out of 10, it just won't work out because of impossible cuts elsewhere.