I have a 1930 semi-detached bungalow in the east of Scotland. The walls are two leaves of brick with a finger-width cavity between, tied occasionally with a course of brick. 100mm cork IWI has been added, with Secil lime-based adhesive and finish. The existing harling (wet dash) is cement-based, with what I presume is a modern 'non-breathable' paint finish. The harling seems sound apart from where building work requires patching. My question is whether the harling should be replaced with a lime-based finish (K Rend's K Lime Roughcast has been suggested) + silicate paint to allow any moisture in the wall a route out to the exterior as well as the interior. Or do I ensure the existing harling is meticulously repaired in an attempt to eliminate rain getting in? One traditional lime harling company has suggested that as we get more and more rain a lime-based exterior could at times let damp right through the brick tie courses. The IWI supplier advises leaving the existing (made good) - that would certainly save a lot of money. Thoughts?