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 2 hours ago by saveasteading