Tips on foam to stick PIR (flooring) together?

[Great_scot_selfbuild]

I’m busy installing PIR flooring insulation (on top of beam & block floor, to then have a dry screed laid on top. 
 

We have the DPC down, and it’s all going together fairly well. 
 

I understand expanding foam is typically used to help fix them all together and generally fill the odd gap (none are large). I’m worried about the foam getting underneath and lifting the boards.

 

1. How much foam is typically needed (assume the sheets are tight together)?

2. Any tips on installing the foam?

3. Do I need to be worried about the foam lifting sheets, or will it only really expand where there’s a gap for it to?

 

TIA

[JohnMo]

Do everything a tight fit and foam any small gaps, rather than wholesale foam every piece. I did every joint tight and knocked in place with a piece of wood to spread load and a mallet. Go around edge slowly to insert square not at an angle.

 

Ideal is it needs no foam, but sure that is realistic. Then I taped all the joints.

[Oz07]

I never used any in this type of scenario. Just cut a tight fit. You'll be on a flat enough surface with it being b&b should be able to keep everything nice and flat and square. 

[saveasteading]

Agreed as above. No need to stick them down or together. I think I  would ignore any gaps up to 2mm, as the tape and over-sheeting of dpm will create a closed cell. 

In any bigger gaps  i'd be wary of squirting in foam, for the reason you suggest, , and more comfortable trowelling some in. Or make some slivers and press in.

Edited Monday at 18:23 by saveasteading

[Great_scot_selfbuild]

Thanks all - the fit is pretty good tbh

[Redbeard]

If you do have bigger gaps cut down each side of the joint to the base of the PIR, so you have an open V with the wide (not that wide!) part on the top of the PIR, facing you. Then it is quite an easy job to start foaming at the bottom of the V and slowly bring the nozzle up till you have filled to the top. Of course you can stop before you reach the top as each squirt expands, but knowing when to stop takes a bit of experimentation. The tape over as VCL. I prefer to use air-tightness tape rather than foil tape.