underfloor heating and tiles but what floor type

Hi,

We have laid underfloor heating pipes with 50mm insualtion underneath on a suspended timber floor.
We plan on screeding this to the top of the joists.

What im not sure about is what we should use underneath the tiles ...
If we use 18mm T&G chipboard, not usre if one can tile straight onto chipboard ??
Additionally what would be the best product to use to ;
1. Let heat through from the pipes below
2. If we do use WBP ply it doesnt "jump" ?

Real confussion; the home owner doesnt want the floor level raised too high either. Any help would be much appreciated guys !!!

Under no circumstances use chip (crap) board, it’s probably the worst possible tile base you could imagine.

Presumably this is this a suspended ground floor? How are the joists supported, directly off the slab or suspended above it? If so how? size/pitch/span of joists? Will the screed be supported, from the slab or directly over the insulation? How thick is the screed? How deep are the heating pipes in it?

Sorry for all the questions but trying to establish exactly what you have first.

Ishvinder said:

2. If we do use WBP ply it doesnt "jump" ?

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Sorry don't understand what you mean

Hi Richard,

yes its a suspended ground floor. The existing Floor joists at 400 centres, 50mm insulation sheets in between the joists supported with 2 x 1 timber.
The existing floor joists were reinforced at various points. Joists are supported with the existing and new pier brick work which comes up from the ground.
there wont be any screed; using aluminium sheets for the under floor heating pipes. The heating pipes are attached using clips to the insulation boards
they sit level with the top of the floor joists.

The reason we haven't used WBP ply is after doing a lot of research;
1. The heat from the under floor heating pipes needs to reach to surface tiles
2. Unless a thick ply is used anything thin would Flex causing tiles or grout to crack
3. After looking at Bal website (and few others) "I understand" a Latex based primer (or something similar) should be sufficient to cover the chipboard on tile straight over no? Its like a rubbery type thing you paint onto the chipboard and tile over. Apparently one shouldn't think about using PVA not sure why though.

Many thanks.
Ish.

1st..the 50mm insulation...is this the spec..for the wet underfloor heating???...sounds a little thin to me...

normally 175x50mm c16 joists 400c/c...then mfr usually state min 100/150mm insultion,give celotex/kingspan a call on that one mate..

for overboarding then look into knauff,brio boards...

dont forget exspansion joints around perimeter off the room and movement joints also at door thresholds etc..

Ishvinder said:

The reason we haven't used WBP ply is after doing a lot of research;

Click to expand...

I’d be interested to know what research recomends using chip flooring in favor of WBP ply.

Ishvinder said:

1. The heat from the under floor heating pipes needs to reach to surface tiles

Click to expand...

Obviously

Ishvinder said:

2. Unless a thick ply is used anything thin would Flex causing tiles or grout to crack

Click to expand...

I don’t follow that, 18mm WBP will be far more rigid than 18mm chip & a much better choice. You don’t give size & maximum span of joists on the brick piers but 18mm WBP may be sufficient on it’s own; if you use crapboard, you should definitely overboard with tile backer.

Ishvinder said:

3. After looking at Bal website (and few others) "I understand" a Latex based primer (or something similar) should be sufficient to cover the chipboard on tile straight over no? Its like a rubbery type thing you paint onto the chipboard and tile over.

Click to expand...

Personally I wouldn’t tile onto chip in a million years, your taking a huge risk even with expensive latex based tiling products; but your decision.

tictic suggests Knauf Brio boards; not used them personally & after a quick look, unsure if they would be suitable for suspended timber floors.

Ishvinder said:

Apparently one shouldn't think about using PVA not sure why though.

Click to expand...

Standard PVA remains water soluble; if it gets wet it will re-emulsify & your tiles will fall off/float around. You should only prime a tile base if the addy manufacturer recommends it, with most powder based adhesives, they don’t; exception is using powder addy over gypsum based plaster or screed.

The problem will be the deflection of the floor as well as the poor adhesion to chip. a latex product may help with the deflection but wont help a bit with the deflection.

In short your tiles may well stick, but they will still crack due to the bounce in the floor - listen to these guys they know what they are talking about.

brio boards can be used over a suspened floor,as long as you have the floor to spec...
c16/24
correct thickness/width/spans/spacing/dwangs etc..
diffuser/spreader plates
exspansion/movement joints
and follow mfr spec to fixing them...i.e glueing/screwing

have used the 28/33 boards as well for overboarding etc...

the 23 board is for wet u/f only.