Localised Decoupling Membrane

[lmkitchens]

I think I know the answer but I will ask anyway ..

I have a kitchen that is to be in an extension. Part of the original slab is staying, the rest ( 30 m2 worth ) is being wet underfloor heated and traditional sand and cement screed.

I have advised the customer we will either have to line a tile joint along the edge of the joint in the slab and use a Silicon or use a de coupling membrane which would be prefered.

As always cost is brought into question. So I wondered if you can use decoupling membrane just in the area of the joint. There wouldn't be the same lateral movement throughout the screed so maybe it wouldn't be needed?

Was just a thought, I'm getting ready to be shot down!!

 

[Ajax123]

Nope......

 

[lmkitchens]

That's that then! If I convinced the customer to rip up the old section and continue the new screed throughout would a decoupling membrane still be required due to the UFH?

 

[peckers]

there should be put in place an expansion joint from where the new heated screed meets the old screed then the entire floor should have a de-coupling membrane put over it BUT the expansion joint should pass threw the de-coupling membrane and also the tiles!

 

[peckers]

oops you posted another question before i finished, What tiles are being used? If its down to expense (you said cost is involved) it would cost more to rip up the old screed and put the heating in that area and lay new screed?

 

[lmkitchens]

That was part of my question to the customer, I said I would do some more research but It may be more cost effective to tear the screed up, and lay new avoiding some issues!

The whole job obviously we are working towards a price, so I'm trying to make it all add up! I don't cut corners so it's all good fun!

 

[Alan.P]

I would still use an un-coupling membrane throughout, and as said, an expansion joint running through everything to slab at the join.

 

[Ajax123]

If you take up the old screed and replace it with new so there are no joints (bear in mind max bay sizes for screed) then no joints would be needed in the tiles. If you are using natural stone then uncoupling is required. If it is porcs or ceramics the uncoupling is optional.

 

[Alan.P]

And don't forget drying times for the screed and commissioning of the heating BEFORE tiling

 

[peckers]

The new screed area is already 30m2 as ajax has already stated if you take up the existing area too then you have to take into consideration the TOTAL area off new screed which could push you into having to put in an expansion joint or two (Total area unknown to me) across the floor anyway! as well as around the perimeter off the room. And as alan p. has said drying times and commissioning off the heating system has to be taken into account.
Spot on advice! has been given above! I guess it all depends on what can be afforded as to which way you go.