Floor part heated

[aaronhaywood]

Hi got a job to start prepping next week 60x60 porcelain going on 18ml ply with electric underfloor heating in parts!..Its multi room tiling lounge and bedroom will be heated but hall between the to will not. I need to make up the height of the subfloor for the areas not heated, was thinking 6ml insulation board for the areas heated and for the non heated areas to make up the height to top of heating wire with ply..:: latex the lot then cover all in ditra mat . Customer wants floor to be continuous so no door bars can save me, let me know wot you think

 

[Ajax123]

I think disaster waiting to happen. You cannot run an unjointed floor through door thresholds on timber part heated and part cold and not expect it to fall to bits. are there not even expansion joints between the ply sheets?? Run Forrest, run....

 

[Tile seller]

Could you perhaps have a soft joint in the thresholds?

 

[aaronhaywood]

No expansion in joints but does around outside, soft joint would be a good idea prob gunna be charcoal grout so black sili with blend in nice. My other thought is to lay insulation boards everywhere and lay heating where needed then cake it in latex a few times to level the lot

 

[Sean Kelly]

I did a quote a few years ago. The man wanted UFH from the kitchen door to the kitchen sink for his wife for when she is doing the dishes (i.e. a straight 500mm line of heated mat). I told him I would have to SLC the whole kitchen because there would be a 4mm height difference where the mat was. I did't get the job!

Talk the customer in spending a few extra quid on a mat and cover the whole floor in SLC.

 

[Dan]

Also, note that you can get 6mm, 10,20,30,40,50 and 60mm insulation boards. Cheap way to add height where needed and gives customer more insulation.

 

[Dan]

But as said you need expansion joints to go through all layers.

 

[aaronhaywood]

Thanks for the advise guys

 

[SJPurdy]

prob gunna be charcoal grout so black sili with blend in nice.

Charcoal Silicon sealant will look better with charcoal grout!

 

[Dan]

Mapei grout matches their silicones bang on doesn't it?

 

[Old Mod]

Maybe I'm reading this wrong or have missed something.
Why don't u use 6mm boards under heating then outside of heated area use 10mm back fill lower areas with SLC. Then the floor is decoupled too.

 

[aaronhaywood]

Yep that's what I'm gunna do, dident realise you can get the boards in different thickness - will order from tilefix direct

 

[SJPurdy]

decoupling works in conjunction with movement joints, it is not a substitute for them.
Consider a room that is heated so that the floor area expands slightly, the decoupling allows the floor surface (tiles and adhesive) to expand at a different rate to the substrate (still colder under the insulation) without putting a massive shear stress on the adhesive. This expansion is taken up by the compression of the perimeter movement joint (even if its only an air gap covered by skirting). It is also taken up by the compression of the movement joint strip in the doorway otherwise all the tiling in the hallway/next room would be pushed away from the heated room.

 

[Old Mod]

decoupling works in conjunction with movement joints, it is not a substitute for them.
Consider a room that is heated so that the floor area expands slightly, the decoupling allows the floor surface (tiles and adhesive) to expand at a different rate to the substrate (still colder under the insulation) without putting a massive shear stress on the adhesive. This expansion is taken up by the compression of the perimeter movement joint (even if its only an air gap covered by skirting). It is also taken up by the compression of the movement joint strip in the doorway otherwise all the tiling in the hallway/next room would be pushed away from the heated room.

That all makes perfect sense and is a great explanation!
I avoided the subject of movement joints for one very good reason.
I was always taught that if there is no expansion joint in the substrate then inserting one in the tiling is pretty much a waste of time, and that is the rule I have always followed.
Now many years on, I still struggle with the concept that if you put an expansion joint in tiling, (without there being one beneath) that it will be of any benefit.
The way I reason this is, if for example the substrate is continuous through a doorway for instance (seems to be relevant) and you have expansion from a warm room to a cooler one, the warm room cannot push toward the cooler one because there is no expansion.
So which way will it go? To my mind there is only one way it can go, up!
And no expansion joint in the tiles is going to stop the floor from effectively 'blowing'
For it to work effectively surely there must be one in the substrate too?
I'd really like to know the answer to this because it's baffled me for quite a while now.
Thanks.

 

[SJPurdy]

Yes that is something I can't understand either. If there is no movement joint in the substrate what is the point of one in the tiling unless the tile adhesive layer allows some shear movement of the tiling relative to the substrate (which most don't).
If a decoupling layer is used then this allows the shear movement. There must be a gap in the decoupling mat at the movement joint line so that each tiled area can move (expand/contract/vibrate) independently.