Ditra matting?

[simmy08]

I am pricing a job at the moment and i am wondering whether i need to use ditra matting or not.
The customer has built an extension to the groundfloor kitchen and has extended the floor with a support wall to carry old and new joists,and caberflooring 22mm thick to finish. the room size is about 5metres by 4.I have advised that it be overboarded with plywood. My concern is where the old floor meets the new. Diffrerent rates of movement and settlement etc.
The tiles are calibrated Slate.
do i cover the full with ditra? can i get away with covering either side of the new joist to old? do i need ditra?

thanks

 

[marbleman]

the answer is yes, and put expansion joint where old meets new , make sure min 15mm ply is used ,
is it possible they remove the chipboard and start again

 

[simmy08]

the answer is yes, and put expansion joint where old meets new , make sure min 15mm ply is used ,
i must say what is caberflooring 22mm is it chipboard if so make sure deflection is not a problem

yes its 15mm plywood i will put down. So what your saying is i need ditra and an expansion joint? for my future refrence can you tell me why i need ditra and expansion? my own thoughts were that if an expansion joint installed then ditra would be for a any deflection or tiny movement issue then? I thought the flexi adhesive would cope with tiny movements/ vibrations etc. I am new to using ditra so just trying to get my head around it. I just dont want to use it where its not a necessity. thanks again

 

[doug boardley]

you use ditra to combt lateral stress true, but if you have two variable substrates then ditra (or likewise) shouldn't be used to bridge the gap as they may have differing rates of expansion/contraction, (even if essentially they are the same substrate) ditra and expansion joint is the way to do it in this instance

 

[marbleman]

new will move more than old . and adhesive will only take so much movement , expansion joints is recommend , best you read spec on system and how it works and it will help in understanding ok

 

[simmy08]

Any recommendations on a discreet looking expansion joint? couloured or something? i know he is going to ask
thanks

 

[The Legend; Phil Hobson RIP]

Dural do every colour under the sun, also Schluter and Genisis

 

[marbleman]

trimline is another choice

 

[united]

trimline is another choice

or make your own using a nice neat beat of Silicon matching the grout colour

 

[Yorkshire Tiling Services]

For the expansion joint to be effective, the un-coupling membrane should be cut & joined directly over the join between the 2 substrates.
Movement joints should also be placed above any supporting walls or beams.