Closing top of wall cavities before blown in CWI

[Spreadsheetman]

I’m getting CWI (carbon coated bonded beads) added soon to my 70s chalet, but some of the cavity tops are open so I was thinking of closing them off while I do other work in those areas.

 

I have had a look online and there appear to be a couple of types of closer available - cavity socks (which appear to be rockwool in a bag) and plastic laths with EPS/XPS stuck on. Both of those are inconvenient sizes (65mm cavities) and generally have to be bought in batches of way more than I need.

 

I will have a load of rockwool offcuts (rwa45 slabs in 75mm and 100mm) left over from insulating elsewhere so I was thinking of making my own closers by wrapping rockwool sections in plastic netting to keep any bits together (and make it easy to pull the closer out if ever needed). (the netting is also left over spare)

 

Does this sound like a workable plan using stuff I already have?

[Radian]

1 hour ago, Spreadsheetman said:

Does this sound like a workable plan using stuff I already have?

Yes, I did something similar myself only I did it in a hurry the night before the installers arrived so just rammed the mineral wool into the exposed cavity from inside the loft. Worked a treat. What I must do now is go back and fluff it up a bit as when compressed it loses its insulation properties. I didn't want it to be forced out by the beads under pressure though. While they do use around 100psi at the nozzle it's fairly diffuse when spread around the cavity. Having said that, if there is a gap, it just keeps on coming and coming and coming...