/Ah, that's interesting, thanks Jim: cladding the outside is something I've
considered (both on this new wall and the existing one that I mentioned in
an earlier thread). So whatever you used to fix the shingles (mortar?
adhesive?) wasn't affected by the penetrating damp/q
Nah stainless steel screws into plugs in wall, with breathable roofing membrane between wall & shingles...
You need to include a vertical dpm or somesuch in your wall construction to hopefully avoid all that!
Good drainage under the raised bed, and some good dpm lining the 'back' of the wall, lapping a bit away from the wall at the base to 'steer' moisture away from the blockwork?
You can get black dpm if you look about, rather than green or blues that seem to prevail.
Or how about a vertical layer of gravel to form a French drain around the inside of the wall??
Coping stones to reduce rain penetration from above maybe laid with mortar mixed with a waterproofer for belt & braces!?!