That's external mate!!No cavity wall I suspect Tom
I always float square and use skim beads anyway
A few years back I see a house wall being meshed stuck on with board Addy lol , no fixings I assume as the lot was on the floor about 2 days after it was floated with sand and cement lol , days
As you may know, decay of metal reinforcement in external structures is a major issue, even for plastic-coated rebar, in modern civil engineering projects (bridges, etc.). Not just water but also salt (chloride) ingress, etc.