Moonshine

traditional vs liquid screed

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1 hour ago, Oz07 said:

I suspect it was a self compacting concrete

 

I think you might be right on that.

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7 minutes ago, PeterW said:


That equates to £300 per cubic metre... which means that from materials perspective I would go with self compacting concrete laid as early as possible as even if it is around £150/CuM as @Oz07 says it can be laid relatively quickly so I expect with labour you are talking much less. 

 

That is £300 /m2 with labour, is the £150 inc labour?

Also a factor is ufh and the majority that needs to be laid is at first floor level so will need to be pumped, which is going to add to the cost of the concrete option. 

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Concrete pump will add about 300 depending on where you are and how much. You will also have to pay someone to lay they rake, tamp and spray it off not the most difficult but still worth paying someone who works with it regularly. If you allowed a day at 200/250. There are companies that pump and lay (and will quote your supply) also keeping it all in house.

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Concrete around 900 on your figures at 75mm depth (minimum), labour and pump budget 600 so 1500 plus VAT there's not much in it. I prefer the concrete as can get down before watertight and a nice finish floor to work from. Although it depends where in the world you are @Russell griffiths struggled to get reasonable prices locally. I believe @PeterStarck 's second bit at the cherry was self compacting although his contractor might have paid for it?!

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i have a 60mm anhydrite over 140mm PIR. as others say, super flat, fast install. Trad screed can be laid flat but will vary signficantly by skill of installer. Anhydrite does have a slight bounce on the insulation, no one else notices but me but it but I think 80mm traditional would much more more solid. Both take a lot of drying out and the laitance is a factor on anhydrite - but some installers will quote to come back and remove it. You can scrape it off a day or two after being laid, otherwise it seems to bake on and will need a floor sander so expect to pay something along the lines of £200 - £400 for the sanding job in the price, it's fairly obvious where it forms so you can tell when it's been sanded away. Care also needed to ensure later primers and adhesives are anhydrite compatible. It's really fast to lay, ours was done in a couple of hours and walk on the next day. Can be forced dried with UFH aftger giving it a week to cure. Another plus is UFH reaction time in 50mm anhydrite would be quick if that is important. We dont run our UFH much, an hour early evening and it keeps the floor and rooms warm, and I run a UFH temp of about 39 degrees C at the mixer manifold.

 

if I had my time again I would have laid insulation under the slab with UFH embedded, the either floated or ground/polished the slab, or just run a thin coat smooting compound if the slab needed it before finish floor and done away with the screed altogether. 

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3 hours ago, Oz07 said:

I believe @PeterStarck 's second bit at the cherry was self compacting although his contractor might have paid for it?!

No, the second time was the same as the first, except they pumped it and laid it properly that time.

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On 13/10/2020 at 19:09, Russell griffiths said:

 I wanted weight to pin the insulation down with no bounce. 

 

 

This issue weighs heavily in my mind. The simplistic question is "why not 70mm or 80mm of flow screed".

 

No one seems to go down this route, is the reason cost or would 80mm of flowscreed overcook as it cures?

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I reckon cost. The advantage of those screeds is their strength to thickness. I reckon once you get to 80mm your in self compacting concrete territory. 

 

For what it's worth how sure is everyone the bounce is in the screed to insulation movement? I would guess it's the actual suspended concrete floor beams which have a bit of bounce. 

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21 minutes ago, epsilonGreedy said:

 

This issue weighs heavily in my mind. The simplistic question is "why not 70mm or 80mm of flow screed".

 

No one seems to go down this route, is the reason cost or would 80mm of flowscreed overcook as it cures?

Cost, I used 80mm traditional, solid as a rock. 

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2 minutes ago, Oz07 said:

I reckon cost. The advantage of those screeds is their strength to thickness. I reckon once you get to 80mm your in self compacting concrete territory. 

 

For what it's worth how sure is everyone the bounce is in the screed to insulation movement? I would guess it's the actual suspended concrete floor beams which have a bit of bounce. 

My floor beams had far more bounce than I liked, it has now gone, must be absorbed by the insulation and the screed acts as one big paving slab. 

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Wait till it's finished and you have a glass bottle on a hard surface then you'll know.

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2 hours ago, epsilonGreedy said:

 

This issue weighs heavily in my mind. The simplistic question is "why not 70mm or 80mm of flow screed".

 

No one seems to go down this route, is the reason cost or would 80mm of flowscreed overcook as it cures?


Once over 40mm depth your drying times increase greatly.

 

Under good drying conditions (a warm, well ventilated room) Gyvlon Screed dries at a rate of 1mm/day up to a thickness of 40mm and then at a rate of 1⁄2 mm/day for thicknesses above this up to 70mm, the rate may further increase to 1⁄4 mm/day at >70mm:

 

so 80mm of gyvlon screed would take 40 days for the first 40mm and then 60 days for the next 30mm and then 40 days for the last 10mm. So nearly 5 months!

 

I used 45mm of gyvlon THERMIO. I will be using it again on my next project.

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1 hour ago, MarkyP said:

Anhydrite does have a slight bounce on the insulation, no one else notices but me but it but I think 80mm traditional would much more more solid

That was one of my biggest concerns when tiling over liquid screeds. The amount of movement was notable, particularly at the perimeter, and compared to traditional screeds it didn’t exactly fill me with confidence.

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