Best value fixing foam for foil backed boards to painted walls? And maximum thickness it can be used at?

I intend to use mechanical fixings also...

<blockquote><cite>Posted By: Nick Parsons</cite>I would really not use any sort of glue alone on painted walls. If the paint comes off, so do the boards! I use http://www.screwfix.com/p/no-nonsense-expanding-sticky-foam-gun-grade-750ml/6576h - £7.99, or £7.19/can for 3 or more.</blockquote>

<blockquote><cite>Posted By: Nick Parsons</cite>I would really not use any sort of glue alone on painted walls. If the paint comes off, so do the boards! I use http://www.screwfix.com/p/no-nonsense-expanding-sticky-foam-gun-grade-750ml/6576h - £7.99, or £7.19/can for 3 or more.</blockquote>

What about using Unibond or similar?

I have access to plenty of fischer b2 and the firestop foam, will that work?

I have rang fischer and they have said none of their foams are suitable....

I think there are foams made specifically for this purpose. That must imply that the foam bond is rated to be adequate to hold the weight of the board. It will also probably mean the foam is relatively fast to cure and low expansion (i.e. you wont come back in the morning to find all your boards are wobbly becuase they have been pushed 50mm further of the wall as the foam kept expanding.

Is the screwfix stuff actually designed for this purpose? Surely the foam is more to keep the board plumb and the mechanical to stop it falling?

If the adhesive lets go, 2 fixings per board won't stop it flapping much!

No Nonsense Sticky foam ''Can be used as an adhesive for fixing large sheet materials''

On the other hand I use it for sticking foil-each-side Pu boards, followed by battens with mech fixings, followed by boards, so it only has to keep the boards still while I faff about.

The best way to make sure the board/foam/paint/wall interface won't give way is to use battens and screws. The paint is the weakest link - how many layers? or intermixed types of paint?

Posted By: VictorianecoAny idea how many sheets a 750ml tin secures and how many 'dabs' per board.

That depends...sorry. Firstly if your walls are uneven or tilt and you want to make them plumb you can quickly use up a lot of foam. Also if you are worried about the current paint then you can use more say double. So it really does depend. Also I use lines of the stuff not dabs! Perimeter and horizontal usually. Will be putting some up myself on Sat, onto a very dusty uneven wall. I might use a combination of methods. Glue, foam and just a few fixings; the later more to stop expansion sending things wonky and to get it plumb.

I use the orange coloured fixing foam I think it is Soudal brand and I get from Ironmongery Direct but it's available elsewhere. My method is odd, it so I'm told. I just use it to stick the insulation sheets in place and then I counter batten. It creates a service void to run cables then I screw the plasterboard or fermacell to the battens. I would guess I get four or five sheets to the can. I can vouch for the fact that it is very strong. You can't get the boards off whole in the event of an error. It you try it with foil faced board the foil gives before the fixing foam. Grab is minimal though so you gave to prop the in place but it goes off quite quickly. It's the only stuff I have used that can glue polyurethane foam and expanded polystyrene. I've even glued off cuts together to form wider pieces. It's useful but probably horribly bad for the environment.
I'm sure it will hold your composite boards but as others have said, assuming the paint's does too. Be ready with the props. I don't dab, I squiggle all over.

if you clean the foil-faces, dust free, with a damp sponge, the joint will not fail! The foil-facing may delaminate from the C....x XR product, but the foamed joint is strong.
However depending on the orientation of the board, the PIR - foil-face may not be stressed? I have foamed 200mm boards vertically, the foil-face did not shear....

I've used just the ordinary (i.e. "high" expansion) screwfix foam to fix insulation vertically before. In our bathroom I over-battened and added cement board & tiles so that was mainly just to help get the boards up and avoid air movement behind.

However in my garage, for ease of application and because I'm interested in seeing what would happen, I fixed 100mm EPS to the house wall with foam and no mechanical fixings at all. I even foamed 6mm ply onto the EPS as a crude lining - again no fixings. It's still on solid (I can hang off the wall with my hands at the top of the boards, which stop short of the ceiling). I'm not suggesting you do that obviously, but just to reassure that it's a pretty solid fixing.

If you use high expansion foam, obviously it will expand more, but in my experience using a thin bead for adhesion it expands sideways on the back of the board and doesn't lift it off the surface, providing you've got it properly pressed against the wall (I use plasterboard jacks).

Posted By: Dave_07968providing you've got it properly pressed against the wall (I use plasterboard jacks).

Yes, but that's the onerous snag that 'fixing foam' aims to eliminate.

No.

Try a tester if in doubt.

I'm sure there is an 'engineering term' for this phenomenon, but as an example, If you were to put a suction pad (the ones used for glazing) onto the side of a car, you would be able to, quite easily, rock a 2 or 3 tonne car; all that is connection your suction pad to the body of the car is paint. the paint simply does not "pull" off.

It is very difficult to rip off a big swathe of paint from a large area.

Huge swathes of paint simply giving way off a wall doesn't happen (and any kind of insulation board is not really that heavy on a per area basis...)

Dow Instastik went on fine, boards went up a breeze, should have leveled the one wall prior as slightly out but better than it was originally! Will be interesting to see how my taping and jointing pans out... ;-s

DO NOT get this stuff on your beard!!