Trav onto a new screed?

[kev]

Got about 25m of trav 600x400 going down soon, one part of the room is old existing screed and one part is a new screed floor, laid last weekend, there is a wet ufh system in the new screed,i plan to use ditra over the whole area, obviously with spf, but my main worry is how long should i leave the screed to dry before fixing?
Am i rite in thinking i dont have to wait more than about 4 weeks because im using the ditra over the whole lot or does that make no difference?
I believe the screed is about 100 mm.

cheers lads.

kev

 

[Gazzer]

Has the heating been comissioned yet?

 

[kev]

Yes i believe it has... basically the job was already screeded ages ago, but there was a major problem with it, without going into huge detail, it didnt go off as it should, so the suppliers came out, checked it and low and behold, next to no cement in it!, anyway they accepted liability and its all been removed and relaid, this time with a proper mix i'm sure.
Just the customer now wants their floor finished asap. I told them 4 weeks but that i would check to confirm

 

[doug boardley]

do you plan on putting an expansion joint between the old and new floors Kev?

 

[kev]

I did mention that to them, but not 100% sure if i would need one or not, do you think the ditra would eliminate that need? I wouldnt be able to get the joint in the rite place though because the tiles will be continuing on from the already tiled kitchen floor,

 

[kev]

Hi chaps,
Thanks for the replies but anyone got any thoughts on the original question?

cheers.

kev

 

[Ken Bruty]

Hi Kev

If you are planning on laying on a wet screed, it normally has to be a minimum of 7 days old, then you can use a green screed adhesive (2 part) to stick the ditra down with such as Weber rapid set mixed with a 5l bottle neat of AD250 acrylic, then you can use a spf adhesive over the top to fix the tiles (white preferable). And I would defo recommend an expansion joint in silicon over the adjoining old and new screed.

 

[kev]

How would you fit the expansion joint in, i cant get a grout line on it cause i'm governed by existing lines which i will be joining onto. would you just cut the joint where it has to go and silicone it, ?

 

[doug boardley]

Kev, when they laid the new screed, did they just butt it straight up to the existing floor without an expansion joint?

 

[kev]

not seen it yet but i did see the original and there didnt seem to be an expansion joint in that one, so i would imagine this will be butted together

 

[doug boardley]

I know I've deviated from the original question Kev, but I'd really consider putting at least an expansion strip where the old and new substrates meet. Does the existing screed have ufh?

 

[kev]

no , only ufh in the new part . Its split about 50/50 old and new

 

[kev]

i was of the impression that the ditra would be sufficent

 

[Ajax123]

there should be a full depth isolation joint in the screed where the heated meets the unheated area. This should be preformed and compressible to allow the heated area to expand and contract because the heated screed will expand under thermal loading against the unheated screed. Ditra is not designed to replace expansion joints and as the joint in the screed is already not correctly formed I think to not place a joint in the tile face would be to invite problems in the future.

 

[doug boardley]

That's what I was trying to say Al:lol: