Advice on tiling large floor

[heffs]

Hi,


I am about to tile the floor of our new extension, approximately 44 sq metres (9.5m x 4.6m) plus utility room, with porcelain tiles – 500 x 500, 500 x 250 and 250 x 250. The floor was screeded 2 months ago, and has (wet) underfloor heating, which at present is not connected up, and is unlikely to be for some time.

I have been reading up methods/opinions on this (great) site for some time, but still have a couple of points on which I would appreciate your advice.

I realize I should probably use flexi adhesive and grout, but given the underfloor heating, should I also use a uncoupling membrane such as Ditra?

Expansion joints: do I need any, and if so, how is this done?

Setting out: given the different tile sizes, do you have any tips after establishing centre of the room. There are three doors off the main rectangle, one leading to a utility room 3m x 1.5m which will be tiled and one into a pantry 1.2m x 1m which will also be tiled. The tiles will end at the 3rd door.

Thanks for any help!

Heffs

[Pawelzik]

Did I understand you right, that the UFH is not connected and wasn´t checked for function and/or possible leaks? I think this is a matter to clarify at all before you start tiling.
If the screed is cement based and 2 month old all water should have gone and the screed wouldn´t shrink or bend anymore. Therefore a decoupling matting is not a must and direct tiling with a flexible adhesive (S1 flexibility acc. to BS EN 12002) should do.
Expansion joints: Are there any expansion joints in the screed that you can follow?

[heffs]

UFH system has manifolds and is pressurized and tested, just not connected to c.h. boiler yet. There are no expansion joints in screed.

Regards

Heffs

the underfloor heating system must be fired up and gradually taken to full tempreture over a couple of days ...this is vital to the expansion and contraction of the screed...once this has happened you can tile it.....flexi adhesive is fine but i always use an addative to take the adhesive to S1 standard.. (keraquick and latex plus) because there is a lot more expansion with water bourne systems.......
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oh...sorry i forgot to mention the underfloor heating system must also be allowed to cool down to its off state.
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I presume that you are laying a three tile bond.....this type of pattern is very repetative....basically you have your big square with the rectangle directly above and a small square above the rectangle aligned to the left...and a small square aligned to the right of the rectangle..... i hope thats clear....
if you can visualise the pattern (draw it!!!!) all you need to do to set it out is find the middle of the main room (First) and the middle of the adjoining hallway (or main hallway) and where the two lines cross is where you start the pattern...
with these kinds of patterns the lines go everywhere but by doing it this way you make the best look in the main areas....sometimes you can not have it all.....
thats why i dont drive a ferrari......

[Pawelzik]

Complete down cooling of the UFH is not neccessary as no one wants to live in a cold house. But working temperature should not be over 15° C during tile laying and grouting. After grouting is finished keep the temperature at 15°C for minimum 14 days, than raise the temperature in 5°C Steps per 3 days until the full UFH temperature is reached. Afterwards the UFH can be lowered to the normal "good feeling" temperature.

as to last post by pawelzic.....I would check with your manafacturer....i have never heard of an underfloor heating manafacturer advising that the element is on while you install....minimum 7 days off (14 reccommended) .....regardless of how cold it is...adhesive needs to cure in its natural state, using the element will change the adhesives curing process......its all about expansion and contraction.....

[Dave]

15 to 20 dgs is the optimum temp for adhesive to set at the stated time on the bag.....never use adhesives at 5 dgs or below.......i turn ufh off and if its cold i heat the room with a heater.......

[heffs]

Thanks all the advice!

I will not be able to fire up the ufh before tiling. The adhesive will have weeks to cure. This is because we are replacing our oil fired boiler in the Spring with a ground source heat pump (no gas in this village) - but that's for another forum!

But given that the floor will eventually be heated, will flexible adhesive be sufficient, or should I consider an uncoupling mat as well?

Heffs.

[CJ]

Agree with all of the above...........

But the UFH is switched on and brought up to full temp over a period of 2-3 days.......then switched of and left to cool right down to allow the screed to expand and contract............not the flexi adhesive.

If you don't...........you risk the screed failing.

I had this happen to me 2 year ago.

I was told that this had been done (It had'nt) I tiled the floor using flexi addy and grout...........then the heating was swtiched full on (Plumber could'nt be arsed to do it slowly )

Within a few days a 12ft crack had appeared right across the floor. The screed had failed and taken the tiles with it

[Dave]

You can use Ditra on this project no probs...it will allow the screed to expand and contract without any effects on the tile adhesives bed...etc........
An un-coupling membrane is ideal for wet heated screeds..........

heres a video to help.... http://www.schluter.co.uk/produkt_video.aspx?doc=6-1-ditra.xml

so we agree if you use the heat on (over 2 days) cool down (over 1 day)to off.
Use a flexi adhesive (should be S1 standard..i use keraquick and latex plus) and the room is not in poland in winter....meaning at normal uk room temp, you dont need to use a decoupler,you can just tile....provided you have S1 (consult your adhesive supplier).
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p.s keraquick is already flexable....its the latex plus additive that makes it S1 standard...
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p.p.s i have read your post again and you must understand that the screed MUST have the underfloor heating put on and the temp raised over 2 days to max and then let to ool down to off over 1 day before you even think of tiling....otherwise
this is imperative for your exisiting "green" screed to expand and contract to its maximums and minimums.....once this has happend you can tile with an s1 standard adhesive without the decoupler....

[Dave]

You can tile onto it no probs with the correct prep and products..but some screeds(floors) are prone to curling and the ditra etc would prevent any probs transferring to the tiled surface.....some peeps see this as overkill but large floors need it sometimes...i have tiled straight onto large floors loads of times and no probs...but a large heated floor then i would think about an uncoupling membrane...but its down to personal preference and how confident you are with the substrate....... neither method is wrong its just down to choice......