Would liquid screed take care of small bounce in PIR?

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AFT4B

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I have laid 135 square meters of 90mm PIR in readiness for UFH next week, which will be followed by Cemfloor liquid screed.

With a floor this size, I'm sure one can imagine the pig of a job this has been with cuts around doorways, walls, services, etc. :cautious:

The floor is predominately block and beam with some areas of concrete slab. As anyone who has worked with B&B will know, the beams are bowed to allow for bounce/ suspension (?) which means the floor can never be 100% level even after the slurry poured to fill gaps between the blocks etc.

This inevitability causes a bit of bounce in the PIR in SOME areas. I have tried my best to make "relief cuts" and used expanding foam in gaps but the PIR doesn't sit down until some weight is on it. I have sand blinded the really bad areas/ low spots but there is still some movement. :cry:

I am of course time bound as both the UFH and Screed are booked. Should I continue to lose sleep over this or will the weight of the screed push/ keep it down? The depth of the screed will be 45mm. Help!
 
AFT4B said:
I have laid 135 square meters of 90mm PIR in readiness for UFH next week, which will be followed by Cemfloor liquid screed.

With a floor this size, I'm sure one can imagine the pig of a job this has been with cuts around doorways, walls, services, etc. :cautious:

The floor is predominately block and beam with some areas of concrete slab. As anyone who has worked with B&B will know, the beams are bowed to allow for bounce/ suspension (?) which means the floor can never be 100% level even after the slurry poured to fill gaps between the blocks etc.

This inevitability causes a bit of bounce in the PIR in SOME areas. I have tried my best to make "relief cuts" and used expanding foam in gaps but the PIR doesn't sit down until some weight is on it. I have sand blinded the really bad areas/ low spots but there is still some movement. :cry:

I am of course time bound as both the UFH and Screed are booked. Should I continue to lose sleep over this or will the weight of the screed push/ keep it down? The depth of the screed will be 45mm. Help!
Click to expand...
The weight of the screed will deal with it. If you want peace of mind stick a washered screw through into the blocks and pull it down.
 
noseall said:
The weight of the screed will deal with it. If you want peace of mind stick a washered screw through into the blocks and pull it down.
Click to expand...
That's a great idea. Just a long enough concrete screw I guess?

Perhaps I'll do that for those that have more movement than I'm comfortable with.
 
Just remember that the screw carries a lot of heat. One 4mm steel screw carries as much heat as about 100x100mm of PIR.
 
It should be pretty easy to calculate the weight per sqm of 45mm of screed. Judge for yourself whether this is enough to press it down, perhaps by scattering a few bricks or blocks around on it. Weigh a brick on your kitchen scales first.
 
AFT4B said:
Surely we're talking very small %'s
Click to expand...

No, it could be pretty significant if you put a lot of screws in. Steel conducts something like 1,000 times as well as the insulation.

This is normally discussed in the context of walls, where there is a concern that you’ll have a pattern of cold spots on the finished wall surface that will get condensation. That’s less of an issue in your case. But you still don’t want the heat from your UFH being conducted down into the slab, rather than up into the room.

All I’m saying is - don’t think “I’ll add some screws, just in case, it can’t do any harm”. First check if the weight of the screed will be enough to hold it down (per Ivor above); if not, investigate non-metalic solutions.
 
U-values aside, I wouldn't want screw heads anywhere near UFH pipes. The people laying the pipes will follow their plan, which may involve crossing some of those chewed up philips heads, then several tons of screed will push down on the pipes and surrounding insulation.

Screws were probably a well-intentioned idea off the top of someone's head. But not a good one.
 
Ivor Windybottom said:
U-values aside, I wouldn't want screw heads anywhere near UFH pipes. The people laying the pipes will follow their plan, which may involve crossing some of those chewed up philips heads, then several tons of screed will push down on the pipes and surrounding insulation.

Screws were probably a well-intentioned idea off the top of someone's head. But not a good one.
Click to expand...
UFH pipes are cradled and elevated in dedicated clips. The pipes themselves won’t be anywhere near any insulation fixings.
 
noseall said:
UFH pipes are cradled and elevated in dedicated clips. The pipes themselves won’t be anywhere near any insulation fixings.
Click to expand...
Errr no, they're tacked down, against the insulation...

61bH2+7dHHL._SL1500_.jpg


You don't want any screwheads popping out of that insulation anywhere.
 

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