Tom

Thanks Conor, got the ventilation sorted as the build is nowhere near airtight yet. No point dehumidifiers as I'd be dehumidifying most of south Devon! Screed been down for 10 days now.

Hmmm, eleven loops, guess average about 80m each, so 880m. What's the internal bore of Wunda pipe? Lets say 14mm, so that makes about 135 litres - does that sound about right?

I really need to get some heat in to our screed and I'm thinking a Willis could do the job. Is this doable for a keen DIYer? Here is the manifold as it is now (it's the one on the left I need to get heat through). Parts I'm guessing heater, expansion vessel, pump?, thermostat? Thanks all

Here's a pic of one of the areas

Thanks @nod. I've been over the whole area now and while some areas seem easier to scrape than others, there are a few patches where the scraper digs in and the surface seems really soft, the consistency (and colour) of firm putty. Is this normal? It's been down for 10 days now.

Thanks @nod, so my attempt at scraping in the pics above should do? Going over it again with the scraper lifts more off, but less and less each time. Are you saying one pass with the scraper then leave it?

Sorry, don't follow you nod, an hour after what and a pass with what?

@saveasteading I don't think the stuff on an anhydrite screed does though, unless I'm wrong?

Hmmm, I was told a floor scraper would do it, and it's getting a good load up but there's still some left behind. I could keep going with the a scraper I guess, if I wanted the arms of Zeus. Looks like I might have to hire a sander. Is there a time limit for getting this stuff up before it gets too hard?

Not me, but the Nudura distributor is close by www.thefellpartnership.co.uk

Hi all - our anhydrite screedhas been down just over a week and I'm trying to s rape off the laitance. It's pretty hard going with a scraper, but when is enough enough? A few passes with it gets up a good load of the laitance, leaving the surface glassy smoothe but there still seems to be a bit there (see pics) , but do I need to keep going?

Thanks both for your input. Spoke to a firm who would do a condensation risk analysis for me (taking in to account the steel rafters, z purlins etc) and it seems the calculation would take the best part of a day and cost over £1k - and their hunch is that I would need a VCL anyway. So, have bitten the bullet and instructed the boarders to put a VCL in. Gone for a membrane over foil-backed boards due to the detailing needed at board/steel junctions. What's another £4k eh?

Ah, that's the rub unfortunately, the roof build-up has been altered since the architects plans were drawn up, so we're playing it all by ear tbh. Am still trying to get hold of BC...

Thanks nod. It's just unclear why BC say they want it - and it would be good to be able to convince them otherwise. When you provide the VCL what do you supply?

Hi all - I started a thread a short while ago about whether I need a VCL layer in my roof buildup but it disappeared under the waves unfortunately, and I really need some help with this if possible. Can I retry? I have been quoted £4,500 for fitting the VCL to the roof structure as part of the whole boarding/skimming quote which seems ludicrous. We have been told by BC that we need a VCL but I have the feeling this is a decision made without due consideration - and one that is going to cost me in hard earned bunce. (Like when I was told I wouuld need 2x 11kWh ASHPs by one supplier but my calcs using the heat loss spreadsheet indicated I would need a single 8kWh... but I digress) So, the roof make up we have from inside is: plaster board 200mm rockwool 150mm PIR (actually composite panel, so clad in metal sheet) I have taped the seams between the composite panels and foamed round the edges so am happy that this layer is airtight. BC want me to put a VCL between the platerboard and rockwool, so: plasterboard VCL 200mm rockwool 150mm PIR I'm worried that, at best, this superfluous or at worst will just trap moisture when humid air seeps through the inevitable screw holes etc. I have tried to find an interstitial condensation calculatoir on-line but had no luck, other than this German one: https://www.ubakus.de/u-wert-rechner/? but am struggling to make sense of it. Can anyone shed any light on this? Thank you so much! Tom

Sorry, I don't follow you, the info in the link says you can turn the ufh on after a week, which is what I was told. Am I missing something?

its an anhydrite screed which it seems you can put heat through after a week or so

We're using one company to pour, float and polish our slab. They are very good and would be happy to pass on their details if you wanted.

Actually, just remembered, the screed guy says we need to start getting some heat through the screed in about a week, and suggested hooking up an old immersion somehow. What is the best way to do this? Cheep second-hand immersion/tank, or a willis heater perhaps??

Thanks all, feel reassured. Just a slight mid-afternoon panic. The UFH pipes I'd laid everywhere were finally hooked up to the emanifold today, and one was a few feet too short, FML, so it rides over several to cut a corner. Luckily the liquid screed is so sodding deep, and expensive, FML, that it will all be covered.

Just spoke to the chap doing the screed tomorrow and he said not to worry about it, he has done hundreds of floors with pipes crossing under expansion joints etc and never had a problem. Perhaps I'm just over thinking this. Wouldn't be the first time.

Hmm, I can spray a little expanding foam around the pipes at the concrete/screed interface, but I guess I would still have differential movement of the two pulling/pushing the pipes around?

Hi All, hoping someone can reassure me that this is alright. We have UFH pipes exiting our polished concrete slab below floor level and going in to an area that is going to be (liquid) screeded tomorrow. I'm concerned that at the vertical join where the slab and screed meet there will be movement as the two material expand/contract and that this will put the pipes here under repeated stress. Should I be worried? I'm guessing there should be an expansion gap here - but would this make the differential movement of the slab/screed even worse and put the pipes under even more stress? Thanks all

Yep. Moisture resistant. Should have gone for Aquapanel in retrospect