By Peter "Columbus"
I'm a masonry contractor in Truro, Mass. Recently, my crew and
I laid a series of stone arches below the wood-framed terrace
of a new residence. The deck above was independently supported
on structural steel columns that would be concealed within the
stonework, so in this case the arches were decorative.
Nonetheless, they were traditionally built and totally capable
of supporting a structural load. Before trusses, steel beams,
and reinforced concrete became commonplace, nothing beat the
durability and bearing capacity of a stone masonry arch.
A masonry arch gets its structural quality from wedge-shaped
"ring stones" placed in compression around the perimeter. The
overhead pressure is redistributed to the ring stones and down
to the springer stone at the base of the arch (see "How Arches
I always work from plans prepared by a qualified engineer,
so I'm spared the headache and risk of making structural
On this job, we set a series of elliptical arches between core
walls of concrete block built on 12-inch-thick reinforced
concrete footings (see Figure 1).
Concrete block walls provide lateral
resistance to the outward forces at the arch's base points
(left). Structural steel posts, visible at either end of the
block work, support the overhead deck load
We used stainless-steel wall ties, about one per square foot,
to provide a strong connection between the concrete and stone.
After bringing the veneer up to the specified spring line, we
capped it with level granite slabs. The arch construction began
at this point.
Enhancing the Stone
We worked this job with quarried granite veneer stone; flat,
randomly broken pieces of widely varying size and irregular
shape and about 3 to 4 inches thick. The architect specified an
ashlar pattern, in which the stone is dressed to have straight
geometric lines and is laid in angled patterns. My favorite
look in stone masonry is called dry stack, after the original,
mortar-free method of laying closely fitted stone. I always
work with mortar but back-cut the stone to minimize the face
joints. Although the sizes and shapes of the stones appear
random, I consider each one for its size and place in the
overall pattern and cut it to fit. You have to continually
visualize the total installation as you work, which is part of
the reason each stone mason's work is distinctive.
I precut a big stack of 15-pound felt paper into sheets of
various sizes and use those to pattern the individual stones. I
trace the pattern onto the face of a suitable stone with a
lumber crayon or permanent marker. After a few years, you
develop an eye for selecting a rough stone that'll require the
least amount of cutting, but it's still slow going. Each stone
takes an average 10 to 15 minutes of prep before setting it in
place. We processed 196 tons of granite and worked a little
over a year on this one job. And from all that cutting and
dressing, we hauled away around 78 tons of rubble at the end of
the job, a waste factor of about 40% (Figure 2).
Figure 2.An ashlar pattern requires each stone to
have straight, man-made edges and be laid in a close-fitting,
angular design. The waste factor runs as high as 40%, producing
a considerable pile of rubble as the work
It's worth remembering that stone masonry requires a large
staging area for material storage and processing, for a long
time. You may think you've got adequate parking for all the
other trades, but with stone work going on, you may be
surprised. Sometimes I have to park off site, too.