Self level screed with ufh

[terrycoe1]

hi have 5 bathrooms that have been put my way they have under floor heating with a self leveler over the top would i need to prime this at all or is it good to start laying on once its cured for 2-3 weeks and the under floor heating has been run for a few days and left to cool down ??

 

[Old Mod]

Are u sure u mean SLC Terry?
SLC dries in hours not weeks!
Electric UFH or is it wet?

 

[terrycoe1]

i meant its been layed for 2-3 weeks not sure on what underfloor heating has been used i can find out does this make a big differnece then to the prep of the floor ?

 

[Old Mod]

It's just that your thread title says screed and your post says self leveller. Just trying to clarify your situation mate.
Depending on what the substrate is that you're dealing with the heating system could make a difference.
It's always advisable to find out everything you can about what u are tiling on to so that you can make the best decisions.
Tiling blind could lead you in to all sorts of problems.

 

[terrycoe1]

ah yeah my bad hahah well basically as you no im pushing for more work done a few jobs over last few weeks which has now lead to maybe something permanent with a builder who wants regular tiler hes only given me the basic info at mo will ask the questions etc i no roughly where i stand with it all but just wasn't sure whether priming the floor would be necessary so if a self leveler is used would u reccomend it or if a cement sand screed is used would it be advisable to prime also ??

 

[terrycoe1]

its wet underfloor heating also and hes just told me the meter reading is showing 0.5 percent moisture

 

[Old Mod]

What sort of screed is it Terry?
Sand and cement or Anhydrate?
0.5% is ok BUT u must be definitely sure of what type of screed you're dealing with.
has the beating been commissioned?
What tiles are u laying?
Is this a ground floor?
How deep is the screed?
Exactly how long has it been down?
These are all questions u must be asking every time.
A lot of guys prime everything, but u must follow adhesive recommendations and use the correct primer as instructed.
If u use, let's say Mapei Adhesive and Bal primer, and u have a failure then it's ur backside in the sling!! Strictly speaking as far as they're concerned they are incompatible.
So wherever possible try to use the same manufacturers system throughout.

 

[terrycoe1]

its sand cement been down since feb up stairs and ground tiles on the floor granite and slate tiles going down in the rooms i mean priming doesn't take long but obs having to wait till its dry holds up the time it takes to tile be using the same manufacture now hes specified all the above i think priming sounds like the safer route !??

 

[Old Mod]

Errrrrm it's all natural stone yes?
UFH has it been commissioned? (Tested, brought through its heating cycle)
U NEED a decoupler!
Ditra, Dural C++ whatever, but with all the conditions u've described so far, I wouldn't lay anything without a decoupling membrane!

 

[Alan.P]

I always would use a de-coupler with ufh, seen to many failures.

 

[Dan]

As above.

I know I bang on about us overusing decouplers and not trusting our world leading adhesives, but in this case it's going to save Head aches money and a floor.

You really need the builder to understand this too as he's going to have to see the cost and time viable.

 

[terrycoe1]

by the sounds of it yes would this have to had been layed prior to the screed ? its stops cracking in the joints i take it??

 

[Old Mod]

No Terry, it's a matting designed to go over your substrate, it helps eliminate lateral movement in a floor (side to side)
BUT it doesn't eliminate bounce, that's important to remember!
Your screed will expand and contract with the heating and cooling of your substrate (screed in this instance)
Natural stone is very susceptible to cracking in this environment, hence the use of a decoupler, although not a BS requirement, is highly recommended!

 

[Old Mod]

@terrycoe1

Read this carefully mate!

When do I use a Decoupling Membrane??

http://www.schluter.co.uk/media/schlueter_db_6_1_ditra_uk_1212.pdf

 

[terrycoe1]

ah i see so the adhesive goes over the top of the matting reducing moment and expansion of the floor top info do if the matting is there and all the above what i described does the matting go down with a primer then adhesive then matting then tile ?

 

[terrycoe1]

decent t link it pretty much says it all!

 

[Old Mod]

Wow u read fast!
Do u tile that fast? Haha
Yes Terry, u can prime your screed, make SURE u follow adhesive advice for priming.
Lay Ditra on top using correct trowel, butt joint it, if it needs to be a waterproof membrane (like a wet area) then u must seal the joints to make it waterproof throughout the room.
U must seal the joint with Kerdi Keba tape (minimum 125mm wide)
And u must stick the tape to the Ditra with Kerdi Coll, schluters own adhesive. If u don't it could very possibly fail as a waterproof membrane.
Then tile on top as normal.
Back fill the pockets in the Ditra as u go, the serate your adhesive over the top of that and press in ur tile.

 

[terrycoe1]

im still reading it but i can see there is all the info i need based on substrates top stuff tho mate thanks for the advice ! next question tho say if they were large format tiles how would we limit the bounce of the substrate ?

 

[Dan]

I've added a link to an old and good thread on decoupling.

When do I use a Decoupling Membrane??

 

[Old Mod]

I've added a link to an old and good thread on decoupling.

When do I use a Decoupling Membrane??

Thank you!

im still reading it but i can see there is all the info i need based on substrates top stuff tho mate thanks for the advice ! next question tho say if they were large format tiles how would we limit the bounce of the substrate ?

I thought it was sand and cement?

 

[terrycoe1]

right i rung him and explained about the ditra it hasn't been layed its a self leveling that's been used not cement sand screed i think the job is too big for me to take on at this point in time im comfortable building up my work but this requires some one with more experience than me with marble on the walls and slate and granite on the floors if it was a smaller more local job i would have given it ago better to be comfortable with what i can and cant do is there a way i can pass this job on where its more local for someone to actually go take a look etc ??

 

[Dan]

That's very admirable mate. An expensive job if it goes wrong.

Why don't you try to find an experienced tiler to pass the work onto, take a cut, and go do the job with them? Get your experience up a bit.

If you're sure the job is yours then post it in the find a tiler forum.

Tiling Jobs | Find a Tiler

 

[Old Mod]

Wow sounds like a nice job @terrycoe1
That's a good idea of @Dan you would learn a great deal.
Where is it?

 

[terrycoe1]

that's a top idea its in Houghton near Huntington this idea would be brilliant for me as im wanting to push for bigger things but not going to take on something i not 100 percent sure on so if i post this on find a tiler also its a b and b and not only that the owner has stated it will be a great advertising pitch as it will be a well known place ! i mean i have no doubts on my ability but id want some reassurance im doing all the right things its worth big money i suspect !

 

[Dan]

Post everything you know about it but don't let on who the customer is or the builder etc until things are finalised as you don't want it pinched off you.

Square meterage, days expected to take, tile types and sizes etc etc.

Ask people to contact you via PM. Or contact those that express an interest via PM yourself. Share your phone number or whatever via PM not actually in the thread.