New tiled floor buildup

[TJamesS]

Hi all, currently renovating my 70’s property, I have a suspended timber floor with 18mm floorboards. I want some electric underfloor heating with porcelain tiles to finish. There’s a small amount of bounce in the floor, my plan so far is as follows;

Existing floorboards
18mm ply overboard for strength & rigidity fixed with D4 adhesive and screwed at 200mm centres with 30mm length screws
Primer
Electric UFH
Latex screed
Tile

I was also thinking of sealing the gaps in the ply with polythene tape? Or even putting DPM under the ply? To stop the screed disappearing below the ply & floorboards? Or would this cause an issue with damp/condensation?

Does anyone see any problems with the above? Please could you also suggest a suitable primer & latex flexible screed brand?

Thanks all
James

 

[Dave]

Hi. First off you cannot tile to plywood anymore.
I would be looking at seeing why the floor is deflecting. Rectify and then cover floor with min 10mm marmox etc boards. Following installation instructions

 

[TJamesS]

Hi. First off you cannot tile to plywood anymore.
I would be looking at seeing why the floor is deflecting. Rectify and then cover floor with min 10mm marmox etc boards. Following installation instructions

Hi Dave, thanks for your reply, so I’m not planning on tiling directly on the ply, I want to lay UFH on the ply, then cover in latex screed and then tile on the screed

Mainly just looking for advice re DPM/polyethylene tape and some recommendations for primer/latex screed brands

Annoyingly there’s a tight time constraint, so not enough time to remove all existing floorboards and plane/pack joists to the same height, but that’s the main issue at hand, 70’s construction where the joists have settled at slightly different angles/heights, it was fairly shoddy construction in the first place as all the internal/external walls are out of plumb and covered in copious amounts of plaster/buildout at various thicknesses throughout the walls

Just trying to make do with what I’ve got/with the hand I’m dealt really

 

[Dave]

Its the same issue self levelling over plywood. The bond isn’t guaranteed under new regs.
You could use a system like a self adhesion matting that the ufh clips into. Then there is no cement based product adhering to the ply. You also don’t need to slc over these systems.
Check out loose cable ufh systems from Uheat here >>> Decoupling Membranes | Underfloor Heating Decoupling Matting - https://www.uheat.co.uk/undertile-heating-cable-decoupling-membrane/