UFH and unusual floor construction

[ess gee]

Hi All,
My first post! I've tiled three bathrooms before, but walls not floors. I am renovating a house and have a 22sqm kitchen diner with a floor that needs tiled. The floor is a suspended timber floor but under instruction from the UFH manufacturer I counterbattened the underside of the joists and laid 75mm kingspan in them, then laid UFH pipe and set it into a 25mm biscuit screed before putting 22mm chipboard deck above. (I had my heart in my mouth screwing the deck down!)

So now I just have to tile it!

I have 600x 600 porcelain tiles, and they came with a flexible adhesive the manufacturers said I needed to get from them for them to guarantee the tiles.

Do I need to PVA the chipboard deck before tiling?

I was going to spread the adhesive with a notched trowel to a depth of about 6mm, does that sound right? (I made sure my deck is perfectly level)

Basically I am nervous about my first floor tiling and about tiling over UFH. Any advice would be most appreciated

Many thanks
Susie

[ess gee]

Oh and I should say I have 3 bathrooms to tile in this house, one is a wetroom, and one I have glass tiles to use, so you'll probably be hearing a bit more from me!
Thanks
Susie

[david campbell]

i would lay ply over the chipboard or take the chipboard up and replace with ply or tile backerboards as its not suitable for tiling really,then p.v.a is a defo no!!!!!! check with the adhesive you are using to see if it suggests a suitable primer that needs used and a 6mm trowel in my opinion is too little i would probably be looking at a 10mm u-notch minimum

[ess gee]

Oh ok, well that is unwelcome news! I glued and screwed the deck down so it isn't coming up again, also it is already level with the floor in the rest of the ground floor, so I am reluctant to put down ply to further increase the height difference. The UFH company Uponor, ( who have been rubbish from beginning to end), said 22mm chipboard then tiling was the way to go. I guess I'll have to put ply down. Do you think I could get away with 6mm ply sheets if I panel pin them to the chipboard deck?
But then I can only have a certain thickness of wood over the UFH or it reduces its efficiency.
Also what is the minimum size tile spacers I can use between the tiles?
Thanks very much for your help. I guess mistakes is the way to learn. Or paying a professional in the first place but trying to get anyone half decent in Oxford is a nightmare, plus I'm a girl, blonde, and 'sound posh' so I haven't a chance of not getting ripped off!

[Brinkley]

if the floor is free from deflection (solid with no bounce ) lay 6mm backer board over the chipboard dont use 6mm ply the backer board needs to be glued with a single part fleible adhesive and screwed with screws

[Brinkley]

if youwant small joints i would go with a minimum 2mm joint use a flexible grout as well

[ess gee]

Thanks Brinkley, The floor is level and solid with no bounce at all- I laid the biscuit screed perfectly level to the top of the joists so there is extra support form that as well as lots of glue and screws every 400mm. I have to admit I'm not a fan of backer board, but this is based on putting it in a bathroom then discovering you can't plaster onto it! I wanted to tile 2/3 of the board to the edge of the shower then skim the rest. So not really fair to judge it solely on that. I will look into it.

I wondered if I could use a decoupling membrane instead of ply or backer board?

I might also ring Uponor again and ask why they said 22mm chipboard under the tiles. Grrr.

[Brinkley]

if its solid then in theory you can put ditra straight on to chipboard i have seen this advertised by membrane manufacturers

[Stewart]

When you say the floor is suspended, what do you mean.......

[ess gee]

I don't know why it is called suspended timber, I guess because the timber floorboards are suspended between the joists.
Probably teaching egg sucking here but; generally on a ground floor you have brick piers with bits of timber along them, (bracers), and at right angles across the bracers run the floor joists, usually 400mm apart, then the floorboards be they lengths of pine or a chipboard tounge and groove deck run across the joists.

[Stewart]

It's just some people call a floating floor a suspended one which is unsuitable to tile on. If the floor has zero deflection, them I would recommend 6 mm cement board (glued and screwed) followed by a decoupler.