Glue insulation PIR to concrete slab?

[ashthekid]

Somebody has recommended I glue down, with cheap tile adhesive, the 100mm celotex insulation I intend to use before plastic vapour membrane layer, UFH and liquid screed.

Has anyone ever done this before? 

[Nickfromwales]

59 minutes ago, ashthekid said:

Somebody has recommended I glue down, with cheap tile adhesive, the 100mm celotex insulation I intend to use before plastic vapour membrane layer, UFH and liquid screed.

Has anyone ever done this before? 

I can see the logic, as 50mm of LS has little weight per m2. One assumes they refer to the non foil-backed PIR?

Edited May 4, 2022 by Nickfromwales

[nod]

There has been issues with liquid screed lifting the pir I put a couple of plastic knock ins in each sheet 

[jayc89]

Surely the PIR will only lift if screed is allowed to pass through the membrane? I didn't glue our PIR, just fitted it friction tight, taped up and membrane over.

[ashthekid]

1 hour ago, nod said:

There has been issues with liquid screed lifting the pir I put a couple of plastic knock ins in each sheet 

Plastic knock ins?

[BMcN]

35 minutes ago, ashthekid said:

Plastic knock ins?

These.  My PIR was seconds so some sheets were bowed so I used these to hold them down till screed was poured.

[ashthekid]

And they screwed into the concrete easily?

[nod]

1 hour ago, ashthekid said:

Plastic knock ins?

Yes 

A plastic stem with a 50 mil head 

10 mil hole and a couple of taps with a hammer 2 minutes per sheet 

 

Readyfix sell them 

[BMcN]

2 hours ago, ashthekid said:

And they screwed into the concrete easily?

Just drill a hole, push them in and then tap in the centre rod and it spreads out and grips like a wall plug