Foam behind plasterboard

What about the build up of Pressure.

+1

TBH, it's not entirely clear what exactly you plan to do as a whole, and why?

Why would there be pressure, or why is there pressure? Is that an existing issue, or do you mean building up during the filling?

Poly is a catch all term that refers to anything. What poly do you think you are buying? The product linked above is a gap filler not an insulation.

A bit of patching fill behind plasterboard is going to make any noticeable difference. From the description it sounds like you are looking for a thermal improvement, that's good because there won't be any. Acoustic improvements will depend on the acoustic issues.

If the issue sounds penetration? Or sound quality. What you are doing what help with either, but if we know what the issues are we might be able to help.

18 cans was the 2 people in the basement who died. The Boardsie who blew his kitchen up had only used one and a half cans filling in the void behind a wall. It sounds like a bodge job, it's not what that stuff is designed for.

What do you mean by dampen sound. Coming through the wall (including going out), or Echoing, tinny sound within the room - ie sound quality. Two very different things.

Pressure is not the issue. The pressure is unlikely to increase much, and the space is unlikely to be air tight enough to retain air pressure. The issue is that the gap filler contains a propellant. It can explode in confined spaces. I highly doubt you'll need polyfilla to patch the holes. This foam will expand out of the holes and you'll be cutting and sanding it back. I wouldn't be hoping for a good finish ready for painting.

What acoustic properties does the foam have? I would expect its sound absorption to be close to nothing. And it's density is far to low to add sound resistant. It is useful for acoustically t sealing gaps around perimeter of a wall, which is maybe the properties the label is referring to. That will be no benefit on the face a black wall. Honestly think its a waste of time and money and all it will achieve is ruining the finish of the wall.

Insulated slabs are not a good solution here either FWIW.

I would suggest removing currently dabbed slab and replacing with an insulated slab. As its only one wall, disruption should be limited.

Is the dabbed board on a good dry wall? if not, you could do an isolated stud when renewing slab.

Attempted to fill the gap around the dabs would be awful messing and of little benefit imo and would possibly be in danger of pushing the slab off the wall depending on how any foam would set.

Dont do it.

Sound absorption panel deal with internal sound don't much to prevent sound going through the wall. Internal sound in reverberation (echo).

Foam behind the wall will do nothing for sound absorption. The sound waves will reflect off the Plasterboard. It also won't so anything to stop sound passing through the wall. For that you need mass. This foam is very low density. Compared to the block wall it's not even there. If I need to design acoustic plasterboard lining, it would be a min of 50mm of 14kg mineral wool.

It's not that its time consuming or expensive. It's that it won't help to any perceivable degree.

Being rated 60dB is meaningless. A paint could be rated for 60dB. Just means it won't fall off the wall if you play loud music. Sound absorption is measured in NRC, sound resistance is measure in RW or DW. This product has neither product. If you have sound leaking through holes in the wall this will help block up the holes. But to stop sound passing through the solid wall, nada

Pumping the cavity like this is a waste of time to be honest and could even do more harm than good in terms of cold bridging, giving moisture something to travel across. Although dot and dab is probably doing that as it is. 40mm Xthratherm built on an independent wall liner wound be the best job.

That was my assumption at first too tbh. As the foam is some what like PIR in consistency. May even be a PIR derivative.