Travertine over mixed sub floor with underfloor heating.

[7doughnuts]

Hi All,

I'm after some advice regarding the preparation of the subfloor for a travertine installation.

I have just finished an extension which has a concrete subfloor with wet underfloor heating and 80mm screed on top of insulation. The existing property is supended wooden floor. I want to lay travetine throughout and had planned on putting 18mm plywood over the whole floor to cover the transition and strengthen the suspended floor etc.

I have concerns that the underfloor heating may not work as efficiently if I lay ply over the top of it, and wondered if it would be best to ply over the suspended floor and then use a self leveling screed or something over the existing screed to get the levels the same (make up the 18mm)?

The concrete screed has been down since the summer and I have checked it's moisture content with a meter.

Regards,
7d

[Stewart]

What is the construction or your suspended floor made up of?


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[7doughnuts]

What is the construction or your suspended floor made up of?

The suspended floor is 8" x 2" joists (from memory) which are supported quite regularly, there's certainly no noticable bounce. It's a solid 1930's property.

[7doughnuts]

22mm floor boards on top of the joists.....should have said!

[Stewart]

You could replace the floor boards with 22 mm ply and add extra noggins between the joist for added strength for starters.


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[7doughnuts]

You could replace the floor boards with 22 mm ply and add extra noggins between the joist for added strength for starters.

I don't really have an issue with the strength of the suspended floor, the question was really relating to whether I should continue the ply over the concrete floor or stop at the transition and screed up to it so the underfloor heating worked effectively? Or are you saying replace the floor with ply and noggins so the levels are the same anyway?

"I have concerns that the underfloor heating may not work as efficiently if I lay ply over the top of it, and wondered if it would be best to ply over the suspended floor and then use a self leveling screed or something over the existing screed to get the levels the same (make up the 18mm)?"

[Stewart]

If you replace with ply, then floor stays at the same level, so no need to ply over screed, which would cause problems with the heated floor IMO. I would then recommend using a decoupler over the whole floor fixed with a quality SPF adhesive. You would also need to have an expansion joint between the two substrates.....


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[7doughnuts]

If you replace with ply, then floor stays at the same level, so no need to ply over screed, which would cause problems with the heated floor IMO. I would then recommend using a decoupler over the whole floor fixed with a quality SPF adhesive. You would also need to have an expansion joint between the two substrates.....

The problem is I've already worked out the finished floor height to take in to account for the 3/4" ply, and there are bi fold doors with recessed bottom track etc for a seamless transition.

Would the next best option be to lay the ply over the suspended floor and then screed up to it, and lay the decoupling membrane over the whole lot? How expensive is the decoupling membrane and how thick? I've got about 55m2 to cover! Not as expensive as re-tiling the whole jobe I guess!

What sort of expansion gap is required between the screed and ply, 10mm? Does the tiler just tile straight over the gap?

Thanks for all of your advice

7d

[7doughnuts]

just a quick bump on this as I need to make a decision soon and get the ply down.

Thanks for all of the advice so far

[enduro]

I had the same problem last year with a builder...he plyed over the screed then i tiled. And the underfloor heating still works a treat. Very fussy customer and had no issues with it.

[7doughnuts]

Thanks for the reply enduro.

Do you know if he put a DPM under the ply (over the screed)? There's one under the screed and the slab so I'm guessing it's not required. Probably worth putting one over the suspended floor I would imagine but would welcome opinion?

[enduro]

They where laying an oak floor on half of the screed and other half where tiles. They primed the screed then glued the ply to the screed with the same glue the where using to fix the oak. (dont screw it to the screed as you will hit the wet underfloor heating)