Wet ufh screed

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Wet ufh screed

Discuss Wet ufh screed in the Australia Tiling Forum area at TilersForums.com.

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Rossymcg

A question for anyone in the know, I'm retro fitting wet ufh down stairs in my house, I'm taking up the timber floor boards acro proping the timber joists to help carry the addition load,fitting Kingspan in between the joists, then the pipe work,
The screed to use is my question, does anyone know if I could use a standard concrete mix if not why not? I've been involve many times in new build wet ufh, where we've used sharp sand and cement damp mix and the pumped flow screed, but I'd only be doing a room at a time and would be better if I could mix the concrete and lay myself
 
Chalker

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Normally when I'm fitting ufh between joists, I fit kingspan on bearers between the joists 50mm below the top. Clip the pipe to the kingspan and fill the gap with a weak sand and cement. Then self level the whole floor. Install edge insulation around the perimeter for expansion, Then lay fermacell over the top. It's a quick heat up and you can tile or carpet straight on to.
p
 

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Rossymcg

Chalker said:
Normally when I'm fitting ufh between joists, I fit kingspan on bearers between the joists 50mm below the top. Clip the pipe to the kingspan and fill the gap with a weak sand and cement. Then self level the whole floor. Install edge insulation around the perimeter for expansion, Then lay fermacell over the top. It's a quick heat up and you can tile or carpet straight on to.
p
Click to expand...
it an old house and the joists are only 100mm deep, I was considering fixing the Kingspan to the underside of the joists, minimum dept for sand and cement screed with ufh is 75mm which would have left me with 100mm to fill with concrete, but the 100mm of concrete is quite a bit of mass to heat up,
i like your style with this way, how come only a weak compo mix?
 
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Rossymcg said:
it an old house and the joists are only 100mm deep, I was considering fixing the Kingspan to the underside of the joists, minimum dept for sand and cement screed with ufh is 75mm which would have left me with 100mm to fill with concrete, but the 100mm of concrete is quite a bit of mass to heat up,
i like your style with this way, how come only a weak compo mix?
Click to expand...
You will get 75 mm with the system I proposed. 50mm of screed and 25 mm of solid fermacell. If you are tiling, that is also part of the mass. The screed is a weak mix as its not structural, its just there as mass.
 
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Ajax123

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If your joists are 100mm you can put 70mm of king span supported on bearers then on top of that 30mm of Gypsol TimBRE screed on top. That will bring you to the tops of the joists and you can put your floor boards down. The performance of anhydrite vs concrete is about two
Twice as responsive. And will give you better performance at lower flow temperatures.
 
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Rossymcg

Ajax123 said:
If your joists are 100mm you can put 70mm of king span supported on bearers then on top of that 30mm of Gypsol TimBRE screed on top. That will bring you to the tops of the joists and you can put your floor boards down. The performance of anhydrite vs concrete is about two
Twice as responsive. And will give you better performance at lower flow temperatures.
Click to expand...
Can I buy the gypsol timBRE in bags and mix myself? Or does it come ready mixed on the back of a wagon?
what makes it twice as responsive?
 
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Ajax123

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Rossymcg said:
Can I buy the gypsol timBRE in bags and mix myself? Or does it come ready mixed on the back of a wagon?
what makes it twice as responsive?
Click to expand...

you could buy sureflo in bags from CCF which is the same thing to all intents and purposes. Or you could have it mixed on the back of a wagon. When I did my lounge I needed just under a cubic meter which I mixed by hand. It took a couple of hours. What makes it more responsive is to do with compaction, mass and the fact it is gypsum which is inherently more conductive than cement based screed. Thermal conductivity of sand cement screed is approx 1.1W/m2k whereas Gypsol sureflo is around 2.2. It is self compacting which means no air entrapment. Air is a good insulator so you don't want it there. Because Gypsol is a thinner screed option it has less physical mass to heat up so is more responsive.
 
R

Rossymcg

Ajax123 said:
you could buy sureflo in bags from CCF which is the same thing to all intents and purposes. Or you could have it mixed on the back of a wagon. When I did my lounge I needed just under a cubic meter which I mixed by hand. It took a couple of hours. What makes it more responsive is to do with compaction, mass and the fact it is gypsum which is inherently more conductive than cement based screed. Thermal conductivity of sand cement screed is approx 1.1W/m2k whereas Gypsol sureflo is around 2.2. It is self compacting which means no air entrapment. Air is a good insulator so you don't want it there. Because Gypsol is a thinner screed option it has less physical mass to heat up so is more responsive.
Click to expand...
Sureflo sounds the one, I don't have meters and meters to justify ready mix,, I know ccf well and will talk to them on Monday,
cheers Ajax
 
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Ajax123

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Rossymcg said:
Sureflo sounds the one, I don't have meters and meters to justify ready mix,, I know ccf well and will talk to them on Monday,
cheers Ajax
Click to expand...

You might struggle with your local CCF. If you do ask to speak to Matthew farmer at the Leeds branch. Tell him Alan Jackson sent you...
 
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Rossymcg said:
Ajax another question,
could I use the sureflo with the 100mm joists having 75mm Kingspan in between the joists, pipes on to the Kingspan then the sure flow at a depth of 50mm covering the pipes in between the joists and 25mm on top of the joist height?
Click to expand...
you will still need the fermacell to decouple from the joists expanding.
 
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Ajax123

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Rossymcg said:
Ajax another question,
could I use the sureflo with the 100mm joists having 75mm Kingspan in between the joists, pipes on to the Kingspan then the sure flow at a depth of 50mm covering the pipes in between the joists and 25mm on top of the joist height?
Click to expand...

You might get away with 25 mm cover to the joists but I would aim for 30mm personally to minimise any risk of cracking.
 
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Ajax123

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Rossymcg said:
Yes 30mm is no drama, are you saying I should also put a dpm covering the insulation and joists to decouple the screed from the insulation and joists
Click to expand...

Yes. This will provide what is called a slip membrane and will also help to keep the screed on top of the system avoiding any leaks... Bear in mind it will be a liquid screed when you pour it. Clip the underfloor heating pipes to the insulation between the joists. How much space do you have available over the joists. If you have room you could overlay the joists with a 15mm OSB deck screwed through and put the screed on top of this. You would need 40mm in that instance so total 55mm over the joists. You would then have a composite floor and no need to notch the joists to allow the pipes to pass across them. Just adds a bit of flexibility to your design but obviously reduces the floor to ceiling height.
 

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