Wet UFH - Straight onto screed or plywood?

[Indy]

Hello all,
Can't quite believe my luck that I've stumbled across this forum as I'm looking for a professional tiler in the East London/Essex area. :hurray:

I have a question before I get a tiler in though. I am laying UFH in the ground floor of my house, in some areas it will be on a concrete floor and in others it will be housed in a suspended floor. Do I need to plywood over the 3" screed in order to get a level floor for the tiler to work his magic on or do the tiles go straight onto the screed?

I am planning on laying 600sq stone tiles on the entire ground floor roughly 112sq/m if that helps.

Cheers

 

[Gazzer]

Hello and welcome. Yes you have come to the right place. I think having a chat with this guy would be good
http://www.tilersforums.com/members/garythetiler.html

 

[Indy]

A builder friend called me to discuss the matter and his advice was to use 12mm plywood only in the areas where I have a suspended floor, this is to spread the load just in case something large and heavy falls onto it.

More investigations to follow..

 

[Dontiler]

if you planing to use UFH > electric 1! then you need overlay concrete floor with insulation boars other way you will be heating concrete and you UFH will be not effective, where concrete meets plywood I would recommend to use expansion gap for the tiles (about 5mm), 12mm plywood is to thine for the stone, you should use 18mm plywood, then prime the plywood, stick insulation boards with flexible adhesive, then UFH, then latex all floor, then use Uncoupling membrane, then you can lay stone.
good luck

 

[Daz]

I think you need to consider possible expansion gaps where the substrates meet, and also a decoupling membrane such as Ditra across the whole floor. You may be inviting trouble fixing stone on a UFH floor with differing substrates.