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Author Topic: liquid screed ufh pipes  (Read 3699 times)
eabadger
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« on: November 22, 2014, 09:25:14 AM »

Hello,
   Do any of you know anything about liquid screed? We are getting to the point in our eco off grid house of putting the UFH pipes in and are getting quotes to screed over them as soon as we get them in, so far we have plastic membrane then 100mm of extruded insulation then 250 to 300mm of concrete with added fibres to make it reinforced. Idea as we someone will be at home all the time is to have maximum mass in floor and wall, we are not too bothered about fast warm up.
Anyway first artisan arrived yesterday to quote and said we would need to put in another damproof layer to stop a reaction, anyone heard of this before? He understood the large mass idea but said we must put plastic on top of concrete then UFH pipes then he will pump in the screed at between 50mm and 70mm these are minimum and maximum depths or so he said.
Any thoughts? Or advice? 
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BruceB
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« Reply #1 on: November 22, 2014, 10:04:25 AM »

There can be a reaction between anhydrite screeds and cement based screed/concrete.  Google will enlighten.  You can use something like PVA to seal and prevent the reaction.  The artisans will prefer another taped up layer of plastic to prevent the reaction and ensure their flow screed does not flow away.  Most flow screed can go below 50mm to say 40mm, provided the pipes are well enough covered, but you need to read the detailed spec depending on where they source their flow screed.

For instance around here, tarmac is used by some:
http://tarmacbuildingproducts.co.uk/products_and_services/screeds__flooring/screeds/truflow.aspx

Do not forget that the ufh pipes need to be well secured so that they do not float to the surface.
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eabadger
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« Reply #2 on: November 22, 2014, 11:37:37 AM »

Thanks for reply he did say it could react, our concrete supplier does two sorts of screed, one is cement based and drys quicker but artisan rejected that?
Plan is to lay reinforcing mesh on floor an zip tie the tube to that, I showed the man the mesh and tube and he said fine, he did say he will need to return after 6 weeks and damp test floor before I can tile it. I plan to get a second quote for the cement based stuff, I have done all other works myself but have been informed that this cant be poured must be pumped, not sure why, I now have good access and have many loads of concrete delivered, I initially thought just pour it out and allow it to self level, the concrete floors I laid pretty much self levelled when I used my fantastic vibro poker.
Have about 100sqmtr to do, not sure what cost will come back as, not a clue.
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offthegridandy
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« Reply #3 on: November 22, 2014, 02:21:34 PM »

UFH heating pipes should be water filled and under test pressure when covering over whether pumped or otherwise, and heat kept off for some weeks after so as not to dry screed out too  quickly.
 
If you end up with 2x DPC membranes and the artisan is still concerned about damp  I'd queery whether he was planning to puncture the UFH pipes whilst pumping/screeding.
« Last Edit: November 22, 2014, 02:39:43 PM by offthegridandy » Logged

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titan
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« Reply #4 on: November 22, 2014, 03:48:10 PM »

Flow screeds are self levelling, quickly installed and can be thinner than conventional screeds. Things may have changed but they were all gypsum based and do react with cement based products. They dry out at around 1mm per day so 60 days for a standard 60mm floor. The moisture check is to see the floor has dried out.  The rooms need to be well sealed to prevent leakage and can easily float insulation and ufh pipes. The dried floor will have a skin which can either be sealed or abraded off. After weighing up the pros and cons I went for conventional screed. Personally I think in a new well insulated house a 300mm heated floor will be too slow to react either way.
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Bodidly
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« Reply #5 on: November 22, 2014, 03:48:58 PM »

We had an anhydrite screed. Cost was about 30% more from memory but no concerns about unlevel floors as self leveling. As said there is some issue with these screeds and concrete. Our screed was over the insulation so no issues there but had to use a special primer before tiling because all the tile adhesives were cement based. The primer was something called Uzin PE 260. Was told that a PVA primer was not acceptable.
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