I have tried in the past to have our cavity walls insulated but to no avail as the surveyor deemed our outer stone skin to have too rough/irregular an inner surface for the either fibre or bead materials available to work properly. One said it might work with beads but said they would not guarantee the work for the same reason.
I have now come across "Foamseal" and have their brochure in front of me where "Random stone walls" are one of the ticked applications.
Have any of you used or heard of them?
Mike