A.Steve Thomas, who worked for 15 years in the
stucco and masonry industries, responds: First, in my
opinion, you’ve done nothing wrong in not turning the
corner with your lath. I’m not familiar with your mix,
but the work looks very proper, given the photos you provided.
The north-facing porch (with a 6-foot bottom chord and no
“seasonal” sun hammering) as well as the chimney
escaped scot-free. So you have to look at conditions that exist
only on the south (sunny) side.
Your notes indicate that the stonework was done in the spring,
so I assume that the framing took place over the winter months,
when it was cold and snowy.
It’s conceivable that when the sun started beating down
on the porch roof in the spring, moisture trapped in the
unvented porch ceiling all winter started to “cook
off” and shrunk the 10-foot-long bottom chord of the
partial truss that makes up your porch roof. It’s
possible that the leverage exerted as it shrank flexed the
south (outboard) faces of the columns that support the porch,
and that that movement was adequate to cause a fracture at the
area of maximum extension — on the outside face of the
column but not the inside. Presumably, the north porch
didn’t react the same way because it’s not in the
direct hot sun, plus the bottom truss chord/porch ceiling is
only 6 feet long.
It’s possible, too, that the stone corners themselves are
a minor player in this scenario. I’ve been involved in
stone manufacturing, and corners are no fun to make. An outside
90-degree corner with inadequate “beef” — for
lack of a better word — is much more likely to cause
problems than a thicker product (see illustration). I’m
not intending to criticize your stone vendor, but it might not
hurt to eyeball a box of his corners and see which category
they fall into.
Also, I assume you’ve had the stone manufacturer’s
rep out to look at the job. If your installation details and
mortar mix are endorsed by the manufacturer for your climate, I
wouldn’t change your process.
Manufactured Stone Corners