Appreciate some advice tiling with underfloor heating

[House basher]

Hello All,

I'd really appreciate any advice for a job i've got.

I've got a kitchen to tile which i'm gonna put in electric underfloor heating. When i say "i", waht i mean is, the electrician is gonna sort the unerfloor heating system.

The floor is half floorboards and half concrete which i've screeded to be at the same level as the boards.

What i'm looking to do is board the whole area in 12mm plywood and then attatch the heatiing mats directly. After this i would then look to use flexible adhesive and tile directly on top. I'm using 600x600 porcelain tiles.

Is this a realistic way to do the job? I know that insulation boards do help in the heat-up times and probably the heat-loss, but am worried about the extra height(6mm?) and cost.

I could accept the extra heat up time and heat loss if it was not too great, thereby helping to keep the initial cost down and the step to the kitchen as low as possible.(what is the real heating cost difference over 20 square m if i was to go ahead with this plan?)

Also, what is the correct adhesive to use? Any flexible? The fella in the shop was trying to get me to buy what he said was readymix suitable for this exact situation, then told me it was £35 per 4m square.

As this is all a bit unknown for me, any advice on how to do this and keep the height and cost to a minimum would be greatly appreciated.

Thanks for your time and advice!

[Colour Republic]

Ready mix... £35 for 4sqm!!! I take it you were shopping in Topps tiles??

It's hard to give exact advice without seeing it firsthand but from the info you have given I would go for the following...

First off 12mm ply is not suitable as it is too thin. BS states a minimum of 15mm but in any case the quality of ply in most stores is of poor quality and can delaminate when the moisture from the adhesive hits it. That's another thing don't use ready mixed on a floor and even more so on that size tile, the advisor in store wants shooting for that little gem. What you'll need is a flexible cement based adhesive suitable for UFH. So something like Mapei Keraflex Maxi.

If the timber section of your floor is deflection free and stable then you can go straight on to this with an insulation tile backer board. There are plenty on the market but lets say Marmox. There is no need for the ply. If you have deflection in the timber section of the floor you'll need to sort this out, you can do this by either lifting the floor boards and adding support or use something like NoMorePly which is a concrete tile backer board.

You will need to incorporate an expansion joint where the two floors meet as the timber section will expand and contract at a different rate than the concrete section.

It's advisable to put a layer of SLC over the heating mats to protect it whilst tiling, the trowel can nic the wires if you're not careful. It does add cost and not strictly required but has its benefits. It also means you have a much better chance of replacing a tile in the future without damaging the cable if the need arose

[tictic]

i would probally be looking at lifting your floorboards,and then laying 22/25mm wbp ply primed underside/edges with sbr...and bring level with the concrete floor.

movement joint between the two substrates and follow this up through your tiling.

[tictic]

just read your op again...

600x600 porkies....

ok lay a few out beside each other on a flat surface and check for any "bowing"...(usually in the middle off the tiles)...

if your going down the UFH onto two differant subsrates the YOU WILL be needing to go for a decoupling membrane...homelux/shulter/dura etc...imo..and use a good flexy adhesive and grout....

...and as CR says, a good 2 part latex slc ( F Ball for me).. over the top off the ufh.. tape in down with gaffer tape etc...

[Simon Site Manager]

Ready mix... £35 for 4sqm!!! I take it you were shopping in Topps tiles??

It's hard to give exact advice without seeing it firsthand but from the info you have given I would go for the following...

First off 12mm ply is not suitable as it is too thin. BS states a minimum of 15mm but in any case the quality of ply in most stores is of poor quality and can delaminate when the moisture from the adhesive hits it. That's another thing don't use ready mixed on a floor and even more so on that size tile, the advisor in store wants shooting for that little gem. What you'll need is a flexible cement based adhesive suitable for UFH. So something like Mapei Keraflex Maxi.

If the timber section of your floor is deflection free and stable then you can go straight on to this with an insulation tile backer board. There are plenty on the market but lets say Marmox. There is no need for the ply. If you have deflection in the timber section of the floor you'll need to sort this out, you can do this by either lifting the floor boards and adding support or use something like NoMorePly which is a concrete tile backer board.

You will need to incorporate an expansion joint where the two floors meet as the timber section will expand and contract at a different rate than the concrete section.

It's advisable to put a layer of SLC over the heating mats to protect it whilst tiling, the trowel can nic the wires if you're not careful. It does add cost and not strictly required but has its benefits. It also means you have a much better chance of replacing a tile in the future without damaging the cable if the need arose

Now that's some brilliant advice, and the amount of time CR has spent to write it...top man CR!!!!
The advice has got to be worth a thanks!

SSM