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Joint Preparation: A Job for Pneumatics
Marshall, Philip and Michael Watson. "Joint Preparation:
A Job for Pneumatics" in Restoring and Repointing Brick Masonry.
New England Builder, June 1988.
Proper joint preparation is at least as important as the actual
repointing work. Joint preparation consists of carefully removing
deteriorated or inappropriate mortar from between the masonry or
stone units. Deteriorated mortar, by nature, is not difficult to
remove: The challenge is to remove it carefully to a sufficient
depth. Inappropriate mortar, on the other hand, is typically hard
portland-rich mortar, which can cause irreversible damage to the
Keep two things in mind: (1) all materials eventually fail and
(2) historic mortar does not keep bricks together, it keeps them
apart. With historic masonry, soft lime-rich mortar acts as a sacrificial
material protecting surrounding brick. The point to repainting is
to replace this material in-kind without changing its purpose. It
is inexcusable for masons to sacrifice the bricks – rather
than mortar – by using the wrong materials and techniques.
There are two prevalent methods of raking out mortar joints: the
hand method and the use of electric grinders. You would do well
to consider a third option: We’ve had great success with certain
pneumatic carving tools described below.
Many contractors consider the use of hand tools — a mason’s
hammer and chisel — as the best way to remove mortar, If
you are among those, you’ll have plenty of time to consider
other options while using this slow, imprecise method. Laborious
hand tooling is not simply a matter of time and expense but —
more importantly — of worker fatigue. A weary body and mind
is prone to mistakes, here in the form of irreversible damage.
At this point electric grinders might seem a viable option. Per-haps
they are, but only on moderately wide horizontal joints uninterrupted
by decorative elements such as brick window lintels or decorative
terra cotta. And only if you have the skill to match the power
of this tool.
Rotary electric grinders are frequently dangerous to both the
building and the builder. Work cannot be properly viewed under
the clouds of dust and fast-moving debris generated by a blade
spinning at speeds as high as 6,000 rpm.
A major limitation of electric grinders is that they tend to
overcut into neighboring courses when used on vertical mortar
joints. Also the depth of removal is limited by the working radius
of the blade. A 4-inch blade offers only 1 1/2 inches maximum
raking depth. Yes, grinders have their place, but it is usually
as second or third fiddle to other methods, and always in conjunction
with these preferred methods.
The use of pneumatic tools has had a tremendous impact on the
restoration of historic masonry. Why?
Exactly because of the precise manner and controlled impact of
these air-powered instruments. They remove mortar by causing it
to crumble and fall, First let’s distinguish those tools
that are just “full of hot air” from the precision
instruments that can be employed for masonry restoration.
When most people think about pneumatic chiseling tools, they
en-vision the implements used to re-move mufflers from cars, or
to scale steel, or worse yet, to drill post holes into sidewalks
for “No Parking” signs.
We wish to separate the pneumatic tools described above, which
are totally unacceptable for any restoration work, from the tool
Trow and Holden “Barre” Pneumatic Carving Tool
You might think there is a choice of proprietary pneumatic tools
on the market. Not so, While there is a wide range of tools and
the opportunity to have any tools custom-made, they are all made
by one company, the Trow and Holden Company, a firm that has specialized
in tools for the stone industry since 1890. The company is located
in Barre, Vt., the center of the world’s largest granite
quarry and this country’s finest stone sculptors.
The Trow and Holden pneumatic carving tool was designed as a
precision sculpting instrument and has been used by the arts and
industry since 1890. It made its debut to the public at the World’s
Columbian Exposition of 1893 in Chicago; it carved Daniel Chester
French’s Lincoln Memorial in 1922. Today it details limestone
figures at the Cathedral of St. John the Divine in New York, and
it carves granite angels in Vermont. It is also employed by restoration
masons for removing mortar on properties listed in the National
The reasoning behind its application to restoration work is simple;
if the tool is precise enough to sculpt the face of Abraham Lincoln,
why shouldn’t it be able to rake out loose mortar from masonry?
The difference between the “muffler remover” and
the “countenance carver” tool is this. The Trow and
Holden tool has neither a retainer nor a throttle. This is somewhat
at odds with conventional tool design but does provide for some
unique control characteristics not available with other pneumatic
The Trow and Holden tool has a chisel with a round shank, hand-held
in place in the carving tool with no retainer. A round shank permits
the chisel blade to be oriented independent of the tool, an essential
feature that is impossible with square-shank tools. The absence
of a retainer, or any mechanical connection, enables the mason
to defeat the power of the tool immediately by pulling the chisel
away from the piston, without any other action. Precision is effected
by the tool design which enables one hand to operate the tool
while the other controls the chisel. The elimination of retainer
and throttle hardware has resulted in a surprisingly light tool.
Remember, this tool was developed as a finishing instrument to
sculpt stone for hours at a time without fatigue to the artist.
The chisel blades are tempered and available with carbide tips.
They can be custom-made to any length or width, Even very thin
“butter” joints can be cleaned, and a joint whose
width is the distance between the lines on this page can be easily
raked out. As with other raking tools, the width of the chisel
should not exceed three-quarters of the width of the mortar joint.
This pneumatic tool is available in a range of sizes from those
suitable for fine stone sculpting (or re-moving mortar) to those
suited to heavier and more demanding jobs such as roughing-out
blocks of masonry (or removing failed units). All tools require
a compressor with only 8 cfm at 110 psi for full power.
Once mortar joints have been carefully raked out, any remaining
debris can be easily cleaned with a regulated, light application
of com-pressed air.
The Trow and Holden pneumatic carving tool is about three times
faster than hand raking in removing loose mortar, hard mortar, and
damaged bricks. Keep in mind, the object of masonry restoration
is to restore only that material that actually requires work, with
as little “intervention” as possible.
As with any instrument it takes time and practice to master the
correct use of this tool and its potential. For product and technical
information contact: Trow and Holden Company, Inc., 45 South Main
Street, Barre, VT, 05641; 800/451-4349 (out of state), or 802/476-7221.