freddymercurystwin, hi
The all singing all dancing completely buildings savvy Cavity Wall installer will, it is claimed insert a Baloon to prevent the beads or what ever crap they are now telling us is the best thing ever from filling the cavity below the DPC so that the DPC is not bridged inside the cavity, what these ExPeRt Installers fail to note is that the DPC is already bridged by the external render, must be the very dark sun glasses they all wear???
Why? because the installers are slowly coming under very, very serious pressure from their Guarantor Insurers to ensure that they try to cover all the bases to mitigate a future Claim for a failed installation where the internal walls become complete saturated by the fill failing and causing, very expensive problems?
OK if the Installer installs a balloon to stop the fill dropping below the DPC, FINE, but? how do they ensure that the balloon remains level in the cavity? must have X-Ray Sunglasses? then what happens when the balloon is removed? it appears that Gravity does not affect the bead fill? in that the bead fill will somehow remarkably remain in place, that is it will not fall into the void, however deep it is, which will disturb all the bead fill above to induce voids in the bead fill in all sort of places in the wall?
There is a recent trend for the one time installers to close down the installer business and pop up again as removal so called specialists??? the really nasty and oft time failing Cavity Fill is the dreaded Blown Fiber, this combined with an even moderately porous external brick = you would not believe the cost to repair.
One bit of advice to the original post
chris_o is to ensure that the installer is fully and completely and totally backed up by an insurance product. Check the provenance of the insurer, and Please, Please retain the papers and especially the insurance guarantee, if, and I really hope it does not go wrong this sort of detail may, I stress MAY! be needed if the fill fails.
Then again as I work as an Insurance Claims Surveyor, who knows I may pick up some Surveying work to rectify failed Cavity Wall fill.
There is a burgeoning lucrative industry growing around failed Cavity Wall Insulation, both on the removal side and the associated insurance claim for extensive damage to the property, both internal walls and external render and all associated finishes, believe me an insurance claim like this has an astronomical cost.
Ken.