Tiling onto plywood, over underfloor heating, over concrete/floor board mix?

[simonk]

Hi, just been to measure up a job. Its a large kitchen/diner (About 75 square meters). Currently the sub-floor is a mixture of concrete and floorboards. They plan on battening out all over the floor area (something like 18mm x 50mm softwood battens by the looks of the upstairs ) and then laying a wet underfloor heating system (i.e. plastic pipes everywhere) and then covering with 12, 15 or 18mm plywood. I don't know how they plan on fixing the battens to the concrete, if at all. They are then looking to have either porcelain or travertine tiles laid on top of all this. I'd like to offer them advice on floor preparation before I tile to prevent future problems. Is it feasible to tile onto this? If so, can anyone sugggest 1) if and how the battens should be fixed to the concrete part of the subfloor? 2)What thickness of plywood to use- 12mm, 15mm or 18mm and whether the plywood should be primed before laying 3) How best to tile? (E.g. use ditra/durabase, 2 pt plexi, 1 part flexi?). I think I'll have to put a couple of expansion gaps in just because of the size of the area. Should these be over where the sub-floor changes from concrete to wood? Sorry for all the questions, but this has me a bit sumped and I want them to be happy with the end result.

 

[doug boardley]

I've got something similar to price myself simon, am also scratching my head:smilewinkgrin:

 

[White Room]

Laid on a similar thing in a conservatory without the heating pipes, it was 50x50 battons screwed to the concrete base with green woodchip laid on top, solid as a rock. Yes I did tile on top with sbr added to the mix, a few years ago, have seen it since no problem

 

[Ajax123]

Would it not be better for them to screed over the UFH rather than batten and timber. Is the 50mm batten the depth or the 18mm. Heat transfer will be poor if they just lay pipes and then cover them up with ply.

 

[simonk]

The 18mm is the depth of the batten, 50mm wide. I take your point about the poor heat transfer. They could screed over the pipes ontop of the concrete, but that then leaves them with the problem of what to do with the pipes above the wooden floor board part?

 

[White Room]

Sounds like the planning was bad, wire would been better in this curcumstance

 

[smurf21]

i would suggest boarding entire floor with NO MORE PLY sealed with sbr and layed on flexi as with hardibacker then an electric ufh matt ontop of NMP latexed with slc and tiled with flexi.

Does the floor need to be raised in excess of 48mm .....18mm baton....18mm ply...5-8mm addy 10mm+ tile.

 

[White Room]

I'd be worried on the hight their bringing up the floor, what about door frames

 

[simonk]

Sorry, only able to get to internet intermittently at moment.

They are committed to wet underfloor heating rather than electric mats.

Would no more ply prevent flex on the wooden floor section of the room?
Would there be a problem with the no more ply spanning where the concrete floor meets the wooden floor or would this be a sensible place to put an expansion gap?

Adding nearly 2 inches to the overall height off the whole lower floor is something they are happy to do. They have done something similar upstairs and they plan on adding 2 inches to all of the stair treads to get the height of each step correct. The house is a large Edwardian villa with taller than usual doors so raising the floor height, within reason, shouldn't be a problem.

Just found an overlay product by polyplumb that justs sits ontop of the sub floor and can be tiled over. The heating pipes are fixed into it and it only raises the floor height by about 18mm. I suppose I could get them to rip up all of the floor boards, add extra noggins for rigidity and fix 18mm ply in place; (the ply being wbp or marine and having been sealed with sbr or acrylic primer on bottom and edges) ; then use the overlay heating system to fix the underfloor heating onto both the concrete part and the wooden floor part (which should now be a rigid floor); and then tile over this with 1 pt flexi allowing an expansion gap where the concrete floor meets the wooden floor. Seems about right. ?? :dizzy2:

Would anyone recommend using a decoupling membrane as well (Ditra or dural version) or is that overkill?