flag stones and underfloor heating

[peterd]

Having lived in a heat stealing flag stone floor cottage for years, I'

determined to do something about our 'new' house, which has flags i two rooms. First I'll remove the ugly 1950s lino stuff that was poure over to about 1/4" and does provide some insulation but looks hideous Then what?

The plan is to mark for identification, then take up most of the flag with a mini digger, dig down a further X? inches, lay a plastic dpc lots of insulation / say 4" celotex or similar, bed plastic underfloo heating pipes in cement and somehow... bed the flags back in on top an achieve through more luck than judgement a flat surface. Sounds a bi dubious doesn't it. Your experience welcome!

Any general comments on underfloor heating also welcome

-- peterd

[Dave Fawthrop]

| bed the flags back in on top and | achieve through more luck than judgement a flat surface. Sounds a bit | dubious doesn't it.

*Real* flags were/are never flat so don't try too hard for perfection

[The Natural Philosopher]

polystyrene is cheaper than celotex, and you only need about 3" of it really.

I used simple 4" concrete reinforcing mesh and tie wrapped the UFH pipes to it. You need a pipe every other mesh for a well insulated room, or every mesh for poor..run the pipe in a double spiral to equalise temperatres inflow and outflow IYSWIM. Run no more than 100m of pipe per run, and never ever try and join it under the floor. Bring it all back to a balancing manifold. If you supsect that diferential expamnsion may cause slabs to move, cross teh jon with teh pipe slipp[ied loosely into electrical conduit, so the stress is averaged out.

Then PRESSURE TEST it and KEERP IT PRESSURISED when screeding.

I used slate and tile cement to finish the job. No reason not to use a thicker mortar bed.

You may need a small expansion joint round the walls covered with skirting.

[The Natural Philosopher]

You can cris cross the room with a grid of strings, and lay to that for levelness.

[jacob]

Depending on what your flags are made of: A mini digger would very likely smash your flags or chip the edges off etc. I'd lift them carefully by hand - with bars, wooden supports etc and move with a parcel trolley. You could photograph them to get them back same way, but they never fit the same anyway so you might as well to start from scratch and expect to lose a bit and make good with new stone or concrete. They want to be bedded on soft sand without any cement or mortar and placing tight up together where poss. Wide mortar pointing looks crap but some will be unavoidable but wait until they have been down for a bit and have settled. Use a weak mix. Slightly damp soft sand works like a vey weak mortar under the flags and sets under the pressure and with the clay content drying out.

cheers

jacob

[jacob]

Come to think - if you are bedding in sand then you could miss out the concrete altogether - compacted hardcore/ sand/ dpm/ insulation/ soft sand with heating pipes/ flags.

cheers

Jacob

[Yekal]

I am doing exactly the same as you want to do, I have everything except the flags, the recommened way if doing this with wet underfloor heating is: from the bottom up hardcore whackered, sand whackered, visqeen, 6"concrete,