cement screeding over underfloor heating pipework

I am in the process of renovating a small hairdressing salon. It is having underfloor heating installed, approx 100 metres of pipework over an area of 24 square metres. The existing concrete subfloor will be sheeted with 25mm jablite insulation with the UFH piping clipped onto it. The cement screed will then be laid over the pipework to a total depth of approx 30mm. With 18mm hardwood flooring laid on top of the screed. Everything seems to be straightforward, except for the screed, i would like to mix rapid set cement & sand with a lot of water to create a mix with a fluid consistancy to enable the mix to flow easily and find its own level without much work with a float. question is: Would mixing sand and cement to a very fluid state set well enough to form a level enough surface to lay hardwood flooring onto? Tounge and grooved Glued not nailed! Thanks

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30mm of anything over jablite won't last 2 minutes regardless of strength or consistency - you need more thickness on the screed
Reply to
Phil L

Phil L wibbled on Monday 28 September 2009 22:27

I agree. It won't last 5 minutes. The research I've been doing suggests 70mm at least over celotex.

I'm not even sure an SBR screed would cope with that thickness on a flexible base AND UFH.

The two other options worth considering are:

a) A flexible pourable compound - try phoning F Ball and other makers and see if they rate anything for this. Going to cost though...

b) Have a look at

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They sell UFH jablite foil covered panels with pre moulded pipe grooves. Their installation method is to stick that down with adhesive then tile direcly over using a class S2 flexible tile adhesive.

HTH

Tim

Reply to
Tim W

Bit bllody thing 25mm. Id gor for 60mm if you can..

Minimum depth is about 75mm for screed. You will crack that over jablite

I think frankly that unless I have missed something, you are in a complete mess. Your insulation is too thin and so is your screed.

You would do better to use a suspended real wood floor and run the pipes over more insulation between the joists.

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Reply to
The Natural Philosopher

still needs a lot of insulation under, though, if over a concrete slab.

Jolly nice for an upstairs room though, where heatloss downwards is not such a big deal.

Reply to
The Natural Philosopher

Thanks for the advice... decided to forget about the cement screed and recess spreader plates into the Jablite & fit UFH piping into it, connected to a twin loop manifold, & covered by 9mm ply with the 18mm oak flooring on top.

Reply to
Tommy

Tommy wibbled on Monday 05 October 2009 23:24

If you haven't bought your bits,

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have exactly that, ready made (foil covered jablite with pipe grooves).

Reply to
Tim W

I have most of the materials i need the foil covered recessed jablite looks the business though, maybe next time.

Reply to
Tommy

Tommy wibbled on Tuesday 06 October 2009 09:39

OK.

BTW - I assume you are tiling over this. Don't forget that you will need a flexible adhesive and flexible grout. I would go with Class S2 which is more flexible than S1.

Mapei Kerabond + Isolastic works well for sticking tiles to flexible things, but there are many other options. That's a slow adhesive (many hours setting time) - there are super fast ones that can be made or obtained flexible too.

For the grout, you'll be OK with Mapei Keracolour + Fugulastic liquid instead of water, though there are again many other options.

Don't be tempted to be cheap here - the tiles or joints will crack, especially with UFH.

Reply to
Tim W

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