Our company has been using fiber-cement siding for more than
10 years. While we like its durability, we don’t like
breathing the dust generated by cutting it — not to
mention the potential for developing silicosis or lung
OSHA has established permissible exposure limits (PEL) for
silica and other types of dust. Because levels are measured in
milligrams of dust per cubic meter of air, there’s no
practical way for carpenters to determine their exposure, so
it’s best to avoid breathing the dust altogether. In
Washington state, where I work, the Department of Labor and
Industries suggests the following rule of thumb: If you are
breathing air that contains visible silica dust, you are almost
certainly over the PEL.
Fiber-cement manufacturers are aware of the dust problem and
make some recommendations: Work in a well-ventilated outdoor
area; cut with shears or by scoring and snapping; and if you
have to saw, wear a NIOSH-approved respirator or use a
dust-collecting saw — preferably one connected to a HEPA
vac so that no dust escapes with the exhaust air.
We tried cutting fiber cement with electric shears, but
ultimately we switched to sawing because shears are slow, leave
rough edges, and can’t be used to gang-cut pieces.
Respirators are only a partial solution; they don’t
always fit properly and anyone on site who walks by not wearing
one ends up breathing the dust.
About a year ago we began to seriously deal with dust
collection. We did it both to protect our health and because we
got news of a nearby site where the state fined the siding
contractors for exceeding the PEL while cutting fiber
Get a Good Vacuum
After considering a number of vacuum systems, we purchased the
16-gallon wet/dry model from Dustless Technologies
I chose this machine after seeing it at a trade show: It was
very quiet and I could see that dust did not escape with the
To fully comply with the fiber-cement manufacturers’
recommendations we’d have had to buy the HEPA version.
But because we work outside, we bought the less expensive
standard model, which is designed for drywall and general
cleanup and collects nearly as well as the HEPA model.
Anyway, in most cases, the weakest link is not the vacuum;
it’s the inability of the saw to direct all of the dust
into the hose.
Our cut station consists of a pair of sawhorses with a work
surface — a couple of sacrificial planks — on top.
The vacuum and saw plug into an I-socket 110m (DGC Products,
switch that activates the vac when the saw comes on. In order
to clear the hose, the switch runs the vac for several seconds
after the saw cuts off.
The addition of the vac and hose makes the cut station harder
to move, so we cut as much siding as possible — an entire
side of a house, for example — before changing locations.
To save time we stack the material and gang-cut
The Saw Muzzle (Dust Collection Products, 877/223-2154,
dustmuzzle.com) is an
ABS plastic shield that bolts to the front of a worm-drive saw.
For $60, this is an economical way to adapt a saw you already
own for dust collection. I had high hopes for this attachment
because we much prefer to use worm-drive saws.
We put a Saw Muzzle on the Bosch worm drive that we normally
use to cut siding (see Figure 1). Attached to our vacuum, the
muzzle captured most of the chips and dust we generated. The
problem with the Saw Muzzle, however — at least for us
— is that it blocks the view through the base of the saw.
This isn’t a problem if you use the cutting guide on the
base of the saw, but we prefer to see where the blade hits the
Figure 1.A carpenter cuts first
with a Saw Muzzle attached but the vacuum turned off (left).
When the vacuum is on, some of the heavier dust falls out the
back at the beginning of the cut, but the fine respirable dust
is collected (center). With the vacuum on and the blade buried
in a stack of siding (right), nearly all of the dust is
Other than obscuring the blade, the device does a good job of
collecting dust — in addition to allowing you to use a
The 5057KB was clearly designed for collecting dust: Without
obscuring the cut line, its plastic shroud almost completely
covers the blade, kicking the particles and dust to a
compartment in the rear that can be emptied through a flip-up
door. The saw can be used with or without a vac. Connected to a
good vacuum, it captures probably 90 percent to 95 percent of
the dust. You can use it without a vac by covering the port
with the included cap, but you’ll mainly collect only the
heavier particles; the finer stuff still gets into the air
The plastic shroud on the Makita
5057KB makes for effective dust collection when attached to a
vac (left). When it’s used without a vac, the heavier
dust collects in a built-in dust compartment but finer dust
escapes (above left). The dust box is emptied through a flip-up
lid on back (above right).
Ergonomics. Compared with a worm
drive, this saw is small and light, but for a sidewinder it
seems somewhat bulky. For plunge-cutting, you have to push a
lever near the front grip of the saw to retract the blade
shroud. At first this seemed awkward — it’s not
what I’m used to — but after a while I hardly
Most 7 1/4-inch fiber-cement blades have four teeth to cut
down on dust: Fewer teeth means larger chips and less
respirable dust. The Makita comes with a 24-tooth blade
designed for fiber cement. In this case, the number of teeth is
not an issue because with a vac the saw does an excellent job
of collecting dust.
Although I would prefer to cut with a worm drive, I
can’t cut effectively with the Saw Muzzle in place. So
for now the Makita is my favorite saw for cutting fiber
Except for the unusual dust port on top of the blade housing,
the C7YAK is a conventional looking saw. The port can be
connected to a vacuum or to a dust-collection bag.
Among the qualities that I like about this saw are that
it’s more compact and slightly lighter than the Makita.
An oversize lever makes it easy to retract the guard for plunge
cuts, and there’s no blade shroud to obscure the cut
Unfortunately, though, it collects only about 80 percent of
the dust — even when it’s connected to the vac.
That’s noticeably less than either the Makita or a worm
drive equipped with a Saw Muzzle. When used with the bag
instead of the vac, only the heaviest dust particles are
captured; most of the fine dust escapes (Figure 3). Based on
the amount of material collected in the Hitachi’s bag vs.
the amount collected in the Makita’s dust compartment,
the Makita is also more effective at collection than the
Hitachi when the saws are used without a vac.
Figure 3.With the dust bag in
place, the Hitachi C7YAK allows finer dust to escape (left).
Even with a vacuum attached (right), the saw captures less dust
than the Makita or the worm drive equipped with a Saw
Recently we began cutting fiber cement with a miter saw
equipped with a 12-inch HardiBlade (Hitachi, 800/706-7337,
This method is faster than cutting with a hand-held circular
saw, but dust collection is problematic. With the vacuum
attached, we are able to trap at most 70 percent of the dust
— far less than I expected.
Our current practice is to use the Makita saw, connected to
the vac, for ripping, notching, and any other cuts that
aren’t simple 90-degree crosscuts.
Figure 4.A sliding-compound
miter saw equipped with a Hitachi fiber-cement blade cuts
quickly but does a poor job of directing dust into the vacuum
hose (left). A powerful fan (right) directs dust away from the
operator toward an area where no one is working.
For crosscuts, we use the miter saw and set up a powerful fan
to blow dust away from the sawyer and crew (Figure 4). Although
this technique probably would not be acceptable in an urban
setting, it works for us because we build in a semirural area
with large lots. It’s not perfect, though: While the fan
is a plus in hot weather, it will be a different story when it
Tim Uhleris a lead framer for
Pioneer Builders in Port Orchard, Wash., and a JLC contributing