Hi guys,
Im about to tile my kitchen floor with 600x600x10 mm porcelain tiles.The floor is 22mm t+g chipboard,so my plan is to screw this to the joist then lay 6mm ply(screwed ever 300mm). i was then planning to prime the ply and lay my ufh followed by a small layer of slc then bal rapidset flex adesive and tiles then finally grout with bal superflex.Sadly i only have aroun 30mm to fit all this in, so i am wondering if slc is required,The ufh company so its only a recommendation? Your thought on my plan guys? Many Thanks

Is the chip board floor stable and deflection free? And what is the total area of your floor?


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Its 9m2, Yes the floor is quite good, the house is 3years old.I wou8ld rather thicker ply but sdly cant due to an exterior door

i would forget the ply and install a 6mm cement board.

As kilty, dont get me started on 6mm ply!!!!

if the floor is stable and strong when the t&g is screw and fixed, then i would lay 6mm marmox boards over the surface.
1. it will give you a stable surface on which to tile . 2. it will act as a better insulation for the ufh. 10mm is recommended but if height is an issue, 6mm will have to do.

as for the slc. it will make the tiling a lot easier due to the flat smooth surface and it will protect the ufh if you ever have to lift a tile due to any failures whereas spreading adhesive over wires is a bit more tricky and time consuming but yes, you dont actually need the slc, its your call on that one.

Could i ask whats the issue with ply?the floor is insulated below the chipboard,so is more insulation really required?or does the marmox have other advantages aswell? Excuse my ignorance, Ive done alot of reading about all of these but trying to decifer what is usefull and what is spiel by the companies is proving difficult.Hearing it 1st hand from you guys is a much more benifical in my opinion. My problem with the slc is that the floor is level as it sits and im worried if i start using slc i will end up with hills and valleys so to speak.Many Thanks

The quality of ply on the market at the moment is poor and also it will warp or even delaminate if any moisture gets near it, this will not happen with a cement board. 15mm ply is the minimum recommendation for a tiling substrate. As for the SLC, you will need to cover the heating wires one way or another, be it with SlC or flexible tile adhesive, and SLC is always the better option as you can then tile safely knowing that you won't snag a heating cable with your trowel. Remember the SLC only has to just cover the wires by a couple of mm so shouldn't cause that much of an issue.

hi johnymurchi
as floor high is an issue to you, consider such an installation:
- swap chipboard with 18mm+ WBP plywood
- instead of insulatio boards use smt like this

- then UFH
- ideally you would cover the UFH cables with SLC, as you worry you can fail this stage
consider laying the tiles on pourable addy

Ok Thanks for that,Ive order some of the marmox, which primer would be best to use on the boards? Ive read that slc spreads the heat from the ufh better is this true or just internet spin?

Ah perfect thanks maniek, thats where i have order my matting from and im sure it comes with that stuff for primer so ill use it on the boards, Sadly lifting the floor is not an option as it has a fully fitted kitchen on top of it!

I would doubt the advantages of that primer !

I agree Sir Ramic, such a primer and PLY aren't best but it is some kind of solution when floor high is a real issue