Why Not Do
It Yourself?
There are many good reasons not to rent a cutoff
saw and tackle the job yourself. A major difference
between dry and wet sawing is that a dry blade cuts
by grinding. Forcing the blade to cut too deep or
too fast will quickly wear it out. In fact, the
blade should never become hotter than you can touch
with your bare hand, demanding a slow, measured
technique and repeated shallow passes. New blades
cost $200 and up. Burn one out and you buy it.
Unless the rental outfit thoroughly instructs
you in the proper cutting techniques, you could end
up damaging the tool, the saw blade, or worse,
yourself. A hand-held saw weighs 25 to 30 pounds
and becomes harder to control as you get tired. And
if you should encounter a piece of rebar that just
happens to align with the cut, forget trying to get
through it. Without the surrounding concrete
particles present in a cross-cut to mix with and
clear the metal filings from the abrasive segment,
you'll soon destroy the blade. But how eager are
you going to be to relocate the cut and start
over?
By contrast, wet sawing is just that — a
steady flow of water flushes the slurry from the
cut, allowing the diamond abrasives to aggressively
and rapidly saw the concrete. It's a faster,
cheaper, and higher-quality method.
Another issue is that the type of aggregate used
in concrete varies in hardness by region. In
Florida, for example, soft limestone is the local
material, and saw blades go through it like butter
compared to concrete mixed in New Hampshire, where
hard, igneous rock is plentiful. The saw blade that
comes with your rental saw may or may not be suited
to the local aggregate. A concrete sawing
specialist will have the right blade for local
conditions.
A concrete saw blade's segments are produced in
three hardness groups. Segments are made with a mix
of relatively soft metal and industrial diamonds in
various degrees of friability. When the segment is
properly matched to the material being cut, fresh,
sharp diamond surfaces are continuously exposed in
the process of sawing. Interestingly, the harder
the material, the softer the segment should be.
Green concrete calls for a hard segment, because
the sand and aggregate are not yet fully settled
and locked into the mix and so produce an abrasive
grit that would rapidly degrade a too-soft segment.
Fully hardened concrete presents a homogenous mass
that yields more readily to the cutting action. A
soft segment wears better in hard material,
exposing fresh cutting edges.
It's also important to have a sufficient,
directed flow of water in the cut. Merely wetting
the surface to control dust can actually create an
abrasive slurry in the groove that will kill a
blade in short order. A wet saw is designed to
throw water into the cut by centrifugal force. The
slurry is constantly flushed out, effectively
cleaning and lubricating the segments as they
cut.
The dust produced by dry cutting is a health
hazard. Silicosis is a chronic disease of the
lungs, caused by inhalation of silica dust, which
is often present in the aggregates used in
concrete. A good dust mask is a must when you're
grinding concrete. Protective eyewear is just as
important.— C.S.
"Jack" Parsons, Jr.
Jack Parsonsis a concrete sawing and
drilling consultant for P.M.A.C. and a U.S. agent
for Dimas Lamage, an industrial-grade diamond
tooling manufacturer. He can be reached via e-mail
at
jackpmac@capecod.net.
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