screed with inset timber joists

[Deleted member 18697]

I am being asked to tile a screeded floor which has joists inset into the screed and which are flush with the screed. Does anyone know of a system that can be overlaid before tiling. My concern is that these timbers will expand and crack the floor. The stone is 500mm x random limestone. There is under floor heating in the screed so whatever is used needs to allow the heat through.

 

[peteablard]

Are they not just battens that have been used to get it level?

 

[On one]

How far apart are the timbers? If you are using rapid set adh the expansion could be minimal I would have thought,more likely to be shrinkage of the timber from the UFH over time.

 

[Deleted member 18697]

Are they not just battens that have been used to get it level?

There was a timber floor there before and the floor was screwed into these timbers. They are set every 400mm across the floor.

 

[Deleted member 18697]

How far apart are the timbers? If you are using rapid set adh the expansion could be minimal I would have thought,more likely to be shrinkage of the timber from the UFH over time.

The timbers are 400mm apart. There was an oak floor down before which was fixed into them. Also there is under floor heating in the screed and the pipes run through the timbers at certain points so it will be a pig to remove them and not damage the heating.

The oak floor failed because the room was flooded a while back, so I am nervous that they will expand if it floods again which is quite possible.

 

[nybor62]

i would deffo use ditra matting . if it floods again that;s the floor ruined i reckon ,

 

[widler]

I did one last year, 45m2 , exactly the same kind of floor (apart from the flood bit)
They laid it,turned it on for a good few weeks,turned it right down, laid chipboard over it, fastened to joists,turned it off after a week.
I cement boarded it,slc it then tiled in 1000x500 porca .
Im back there now tiling the bathroom, looks great and warm.

 

[Ajax123]

If the screed is sound and well supported you could screw and stick 6mm hardibacker down to the joists/screed as a tiling surface. you need to make certain there is no deflection or movement though. The good old glass of water and jump up and down test would give you this answer. When the oak floor was screwed to the joists this will have given a good deal of lateral support and thus imprved rigidity. The screed not being composite with the joists is just a dead weight so will not necessarily do this. I wonder hoaw it is all supported underneath.

 

[widler]

If the screed is sound and well supported you could screw and stick 6mm hardibacker down to the joists/screed as a tiling surface. you need to make certain there is no deflection or movement though. The good old glass of water and jump up and down test would give you this answer. When the oak floor was screwed to the joists this will have given a good deal of lateral support and thus imprved rigidity. The screed not being composite with the joists is just a dead weight so will not necessarily do this. I wonder hoaw it is all supported underneath.

The one I did was timber screwed to each joist and ply on top, then pipes then screed,then chipboard then cement board.
The screed must be just to encase the pipes

 

[Time's Ran Out]

Apart from any flood completely blowing the chipboard, what is the screed over by ways of DPM?

 

[widler]

Apart from any flood completely blowing the chipboard, what is the screed over by ways of DPM?

I don't get you john?

 

[Ajax123]

The one I did was timber screwed to each joist and ply on top, then pipes then screed,then chipboard then cement board.
The screed must be just to encase the pipes

The chip board and cement board were a bit of a waste of time really. Why not just tile on the screed. The extra layers must have left it hellishly inefficient

 

[Ajax123]

I don't get you john?

He is asking if there is a DPM under the screed and commenting on the fact that where there is chipboard and floodds the chipboard will blow and fail.... I think

 

[Deleted member 18697]

Apart from any flood completely blowing the chipboard, what is the screed over by ways of DPM?

There is a DPM under the screed but I just had a call today saying they have changed their minds and going to put timber back down! Thats fine I was only starting Monday!!!!

Thanks everyone for all your responses.

 

[widler]

The chip board and cement board were a bit of a waste of time really. Why not just tile on the screed. The extra layers must have left it hellishly inefficient

To strengthen the joists,stop from twisting Alan, surely this is paramount .
The heat comes through no problem, probably less efficient , but the blokes minted