Simon coughed up some electrons that declared:



Yeah, if someone barged into the edge of the opening by accident (2
people passing in doorway etc), I would be concerned the whole thing
could come down. I've seen builders use nails banged into the mortar
courses to hold new additions, which really does a poor job - maybe he
did something like that.
Simon.

Or just banging the door. Even if the plaster firms it up, I personally
would be concerned about cracking the plaster in both cases.

I really hate celcon (etc) blocks. I've never seen ones where the mortar
actually bonds well to them, unlike brick.

With a whole wall, there's plenty of overlap and friction to mitigate but
for random bits like this, bricks wouldn't have taken much more effort...

Cheers

Tim