95sqm onto screed with water based UFH - recommendations?

[Wuffles]

Hi all,

Not been on here for a very long time, kind of dropped out of the tiling business for a while preferring to work with wood and get tilers in on kitchen & bathroom fits, but either way, I'd be out of my depth on this one, and the customer is the missus.

Large extension with screed that was laid last Thursday. We've (that's the Royal we) gone around the houses looking at different finishes for the area, which is mostly open plan apart from a hallway and utility. We've looked at Beton Cire (waxed resin/concrete type of thing), tiles, wood, all around the houses. Probably going to end up with tiles, and probably won't actually fit them myself to achieve a "better" finish.

What should I be looking for on this? I am aware of drying times of the screed for the underfloor heating being in the region of a few months due to the thickness, and I did read somewhere that firing up the heating a couple of times before laying tiles may be a better idea than not - but then that's perhaps open to interpretation? So I am guessing we'll be laying onto a dry screed by that time.

With this size of area should we be looking at having some kind of expansion gap fitted, under-tile matting, Native American burial ground, Pet Cemetery?

Be gentle, just trying to arm myself with info before I get done in by some cowboys.

If you are reading this and are based in Axbridge/Cheddar/Weston Super Mare, don't ride a horse and wear spurs, feel free to give me a wave and perhaps swing by and give me a price.

 

[Dave]

Screed type ?

 

[Wuffles]

Good point. Cement based with fibres.

 

[Dave]

Any idea of tile choice yet , ceramic , porcelain , stone ?

 

[Wuffles]

Well, as you asked, it will most likely be porcelain as we have some nice ones in another part of the house. Closest looking thing to limestone I've seen before. We once had limestone everywhere in a basement flat, and the maintenance was a struggle, but I'm not trying to start a debate.

If, however, people start recommending ceramic over porcelain, I'm game.

 

[Dave]

Ok... Do you have a room plan , like doorways and room direction changes .?

 

[Wuffles]

I do, I can chuck it on Dropbox and link it if that helps? It's pretty straight-forward though.

 

[Wuffles]

Here you go. The grey area is the tiled area. Utility small room bottom left, hallway bottom right, rest of it is open plan living, kitchen, dining, roller-disco, shrine, open to ideas.

https://www.dropbox.com/s/rkmo75odzncdmkm/plan_copy.pdf?dl=0

 

[Dave]

Thanks for that.

so you know how to commission the ufh/screed ok..

i would put expansion joints in the doorways and uncouple the rest of the floor with an anti-crack mat .

new cemenet based screeds will cure over a matter of months and could curl/crack as this process takes place , some might see it as overkill but I see it as peace of mind.

 

[Wuffles]

I was just going to wait a few months before trying the UFH, we're on Air Source Heat Pumps so the water temp isn't dramatically high - we will be plumbing in a temp setting mixer for want of a better word - the kit came with one for use on higher temp systems, but I guess it'll help us out on the whole starting gently and getting hotter ramp some people seem to recommend.

Decoupling would appear to be the way to go, good. Any advantage of ceramic over porcelain? The walls are stud walls, so by expansion gap you mean a product that would sit in-line and just do its job?

Cheers for your time on this. Clearly there's no rush anyway for the tiles. Wait until after the heating's been commissioned before going ahead?

 

[Dave]

By expansion, I mean preformed joints within the doorway openings , the room is way too long with out them and you need to eliminate as much stress as possible.
The width is still over the standard length without a joint but uncoupling imo will suffice to give a better aesthetic look.

 

[Wuffles]

Thought I should resurrect this thread in case anyone's interested.

Still living with screed, haven't got round to doing anything yet as other things have got in the way.

Screed will be very much dry by now and we've bought some flagstones for the patio (22mm thick sandstone) which appear to be usable inside too. Took a chance on them as it was only from a picture, but having seen them in the flesh the plan is now to measure up and order enough of those to do the inside too.

Spoke to a man about the decoupling mat and he advised this will affect the performance of the UFH, which I suppose could ring true.

 

[Ajax123]

Don't assume it's dry just dos it's old. It may have had a year to dry but it's also had a year to get wet again.

 

[Wuffles]

Interesting point.

So we should wait longer or do you mean to say it's certainly dry enough to lay flooring on now but not actually totally dry.

 

[Lee@emctiles]

Spoke to a man about the decoupling mat and he advised this will affect the performance of the UFH, which I suppose could ring true.

thats the wrong information you got there. Dural matting is ideal to use as it lets the UFH through. (as does Ditra)

 

[Wuffles]

thats the wrong information you got there. Dural matting is ideal to use as it lets the UFH through. (as does Ditra)

Excellent information, thank you very much. He wasn't a tiler, but an engineer. I'm just trying to arm myself with knowledge.

 

[Ajax123]

Interesting point.

So we should wait longer or do you mean to say it's certainly dry enough to lay flooring on now but not actually totally dry.

Neither. I mean doa moisture test to determine if it is dry before you tile.As for the uncoupling membrane it is true to say, from a purely technical point of view, that every time you add an interface to the floor you reduce the efficiency of the heating system. However the mass of the uncoupling membrane is so low that from a practical perspective it will make negligible difference. It will cost a considerable amount more if the tiles fail due to not using it if using it would have saved that failure from happening. Its not a massive amount to spend in the general scheme.

 

[Wuffles]

I was hoping that wouldn't be required after 9 months of it being down. Is that normal?

 

[Ajax123]

Up to you. Expensive risk to take if its not dry though for the sake of a quick test. A tester costs maybe £30 that would do the job.

 

[Wuffles]

I meant is it normal for screed to not be dry enough after 9 months?

To be honest, it's not my risk, I'm not the one doing it (although it is as it's our floor, but hope you take my point). I would expect a professional to be checking dryness and giving advice if they're taking on the risk.

All I am trying to do is amass enough information to avoid the idiots that do seem to exist as in every industry.

 

[Ajax123]

No it would be perfectly reasonable to expect it to be dry after 9 months but things can get wet as well as drying out. Depends on environmental factors, floods, spills etc. never assume is my motto these days.

 

[Rizzle from the Portizzle]

No it would be perfectly reasonable to expect it to be dry after 9 months but things can get wet as well as drying out. Depends on environmental factors, floods, spills etc. never assume is my motto these days.

well said at last

 

[Ajax123]

well said at last

What do you mean "at last" ?

 

[Rizzle from the Portizzle]

What do you mean "at last" ?

well some screeds can draw in a lot of moisture from day to day be ok one day to tile but not the next depending on weather conditions and are the windows fitted ie air tight .so you should test again the day you start tilling .and all the way throught .on some screeds .

 

[Ajax123]

You mean calcium sulphate screeds I presume. All screeds do the same thing in terms of equillibrating with the atmospheric conditions. It's basic physics. At the dry stage of the screed It's often a counter intuitive process though. As the atmospheric moisture content goes up the moisture level at the screed surface actually tends to go down as the high vapour pressure in the air prevents moisture coming out of the screed. That's why you can see hygrometer readings change dramatically when the screed and the air are nearing equilibrium. We are shortly to publish a report independently derived about drying and measuring screed moisture which wil hopefully clarify a lot of the myths about drying times and such likes.