The cracks on the edge are probably OK as long as the
mortar bonded fine to the block.
from a reader in Florida:
No, this isn't a stucco expansion joint.
It is a drywall expansion joint.
It can still be used. The mortar would need to
be struck off flush with the
inside edge of the joint.
A joint made for stucco
would leave a much nicer job.
The cracks will fill in with the brown coat.
Note how the stucco expansion has larger holes
for a good key for mortar. The mortar should
Drywall expansion joint with an
Expansion joint for stucco with a 3/4"
squish through nicely for a good bond to the block.
Also, the raised flange has a nice casing for
locking the mortar in place, and provides a neat,
finished edge.On framing where metal lath is
required, the joints should be put on first, overlapping
the side flange with metal lath.