underfloor heating and ply??

**chris303** · 10-03-2009

hi all, i have recently built an extension and have gas underfloor heating which sits into grooves if you know what i mean. the builder has layed quarter inch ply straight over this and says it can be tiled on, is he correct or will the tiles lift with being such thin ply? also what is the best adhesive for underfloor heating or is there little diffrence?
thanx

**grumpygrouter** · 10-03-2009

6mm ply is next to uselss in tiling situations as far as I am concerned. Would need to be at least double that thickness IMO.

**faithhealer** · 10-03-2009

Originally Posted by chris303

hi all, i have recently built an extension and have gas underfloor heating which sits into grooves if you know what i mean. the builder has layed quarter inch ply straight over this and says it can be tiled on, is he correct or will the tiles lift with being such thin ply? also what is the best adhesive for underfloor heating or is there little diffrence?
thanx

Hi Chris, quarter inch ply is a big NO.

**Dave Ramsden** · 10-03-2009

Id have thought that would need a "screed" slab laying over it?!?!

**davy_G** · 10-03-2009

How is the ply attached and is it secure? Its too thin for a start as the other guys have said.
If the UFH is in groves, is it plastic forming boards? Should maybe be screeded over not plyed?

Alot of questions for yer builder ther.
Remember flexi addy & grout must be used.

**chris303** · 10-03-2009

ok thanks all, if i was to lift the ply and screed it then what thickness is required? i forgot to mention the underfloor heating is set into wood, which is grooved and it seems to be solid.
thanx all.