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underfloor heating screed

 
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Woo



Joined: 19 Sep 2011
Posts: 787
Location: Mayenne, Pays de Loire
PostPosted: Sat Nov 22, 14 9:46 am    Post subject: underfloor heating screed Reply with quote
    

We had our first Artisan visit yesterday. Not bad for a project that has been running for 3 years...
any way... questions raised
so far we have sand, plastic, insulation, concrete. next we plan underfloor heating tube attached to reinforcing stuff then the screed or 'Fluide de chappe'. tiles, bobs your uncle....
because of the fluid nature of the 'chappe' we need a pumpist to get it round the tube.
the man who came says we need to put plastic between the concrete and the chappe, because of chemical reactions.
has anyone heard of this?

mousjoos



Joined: 05 Jun 2006
Posts: 1986
Location: VERY Sunny SW France
PostPosted: Sat Nov 22, 14 10:41 am    Post subject: Reply with quote
    

Not heard of that; only to be careful with expansion ("dilitation" with a French accent) & "cold bridges"

so far I've only ever seen the liquid floors poured direct onto concrete...usually any "special" stuff like insulation etc goes under the conrete

crofter



Joined: 11 Feb 2007
Posts: 2252

PostPosted: Sat Nov 22, 14 12:40 pm    Post subject: Reply with quote
    

The method I have seen is compacted base, damp course, 140mm insulation below the slab, 50mm perimeter insulation then one pour of concrete on top of the insulation, (heating pipes tied to the reinforcing) But if your contractor thinks you need polythene you should use polythene, it won't do any harm.

onemanband



Joined: 26 Dec 2010
Posts: 1473
Location: NCA90
PostPosted: Sat Nov 22, 14 3:52 pm    Post subject: Reply with quote
    

Don't see how you would get a chemical reaction between screed and concrete when they are essentially the same thing, just different sized aggregate.
However you should use plastic membrane over foil backed insulation to prevent chemical reaction with the wet screed/concrete. Maybe that is what he meant or what has confused him.

camaro



Joined: 31 Mar 2010
Posts: 178
Location: N. Ireland
PostPosted: Sat Nov 22, 14 8:04 pm    Post subject: Reply with quote
    

I specify this stuff regularly, and if you are doing it from scratch it is amazingly cheap.
I have a building at the minute, approx. 200 square metres. One floor, 5 zones, all to have their own thermostat, all wireless.
2500 quid was the most expensive bid. The boys have it ripped back to a concrete subfloor, apply 100mm of solid foam insulation, then the underfloor heating guys come and staple the hose down to it.
After that, another subbie squirts in a liquid screed - two days later, we can put the heat on.
That price includes the manifolds et all.
£2500 and the cheapest was just over a grand.

perlogalism



Joined: 27 Nov 2009
Posts: 440
Location: Near Welshpool
PostPosted: Sat Nov 22, 14 10:33 pm    Post subject: Reply with quote
    

We had ours done last year and yes, the screed people insisted on plastic over the insulation. Frankly at ~£50 for the DPM and a couple of hours work, it wasn't worth arguing about.

Woo



Joined: 19 Sep 2011
Posts: 787
Location: Mayenne, Pays de Loire
PostPosted: Sun Nov 23, 14 9:49 am    Post subject: Reply with quote
    

Thank you all for your replies.
We know its not worth the hassle for a few quids plastic, it just struck us a strange. but then again maybe its because we are heating the whole mass and most people have insulation closer to the top to provide the barrier.
we await the quote!

henchard



Joined: 23 Aug 2012
Posts: 232
Location: Carmarthenshire
PostPosted: Sun Nov 23, 14 5:26 pm    Post subject: Re: underfloor heating screed Reply with quote
    

Woo wrote:

the man who came says we need to put plastic between the concrete and the chappe, because of chemical reactions.
has anyone heard of this?



Yes if it is an anhydrite screed (calcium sulphate) which can react with concrete.

The usual reason for putting plastic on top of insulation before pumping a liquid screed is to stop the insulation floating on the screed!

As in the photo of ours below


Woo



Joined: 19 Sep 2011
Posts: 787
Location: Mayenne, Pays de Loire
PostPosted: Mon Nov 24, 14 8:40 am    Post subject: Reply with quote
    

Thank you.

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