keep fiber-cement siding
be covered. Note: Use only one nail per stud
blocks of cedar to China to be milled into siding—
covered. It’s cement based and
crossing, preferably 13⁄4-in. large-head nails,
will absorb water, even when
one can argue that fiber cement is a viable green
which look somewhat like roofing nails.
preprimed. Moreover, if you
alternative to wood siding.
Another important detail: Leave 1⁄8-in. gaps
install it wet, the outside will dry
Fiber-cement clapboards come in planks
between the butt ends of boards to allow for
faster than the back, which could
51⁄4 in. to 12 in. wide and from 5⁄16 in. to 5⁄8 in.
expansion and contraction. Behind each butt
result in paint bubbling later on.
thick. Because FC is roughly three times the
joint, affix a piece of flashing tape to the building
weight of wood, 12-ft. planks are an optimal
paper, then caulk the joint with a siliconized
length to work with.
acrylic caulk, which is paintable and typically
comes with a 45-year rating.
WORkIng WIth FC ClAPBOARDS
Unlike wood clapboards—which are lightweight,
SPECIAltY tOOlS
long-fibered, and springy—fiber-cement siding is In theory, you can cut fiber-cement planks with
heavy, short-fibered, and brittle. So although its
hand tools and all but eliminate harmful dust.
layout is essentially the same as that described
But if you’re siding a whole house, a few special-
for wood clapboards, handling fiber-cement
ized power tools will speed the job while greatly
planks is quite different.
reducing the dust.
Whenever possible, carry fiber-cement boards A circular saw with a dust-collection container
on edge—with the width of the board perpendic-
will ideally have a housing over the blade, with a
ular to the ground. Boards will flex less and crack dust port at the rear that connects to a large can-
less if carried that way. For the same reason,
ister vacuum. Makita® has a 71⁄4-in. corded fiber-
always have help when handling or installing
cement saw that is among the priciest available
long boards—it’s not a one-man job. Especially
Exteriors
171
P R O T I P
When you get fiber-cement
siding delivered to a job site, ask
the supplier to unload the truck
by hand rather than rolling the
load off, which could crack the
clapboards. If your shipment is
Use electric shears—also called nibblers—for cutouts in
too large for hand-unloading, ask
fiber cement. Cordless shears are especially helpful when
the supplier to put a layer of
you’re working up on scaffolding, angle-cutting boards to
framing lumber—2x8s or
fit under rake trim, and you don’t want to climb down to
2x12s—under the banded bun-
use a circular saw.
dles to protect the siding as it
rolls off the truck.
Minimizing airborne silica dust is the key to working
safely with fiber cement. Specially designed to contain
such dust, this circular saw features a plastic cover with a
back port that connects directly to a canister vacuum.
Always wear a respirator and safety glasses to further
reduce exposure.
Once you’ve correctly set the air pressure of a pneumatic
coil nailer, you’ll be less likely to crack brittle edges. When
but also one of the most effective in collecting
using a pneumatic nailer, it’s not necessary to predrill
siding nail holes.
dust. Of course, you should still wear a respirator
while using it. FC circular-saw blades typically
have four to eight polycrystalline diamond
nibblers) don’t create much dust, some installers
teeth, which are far more durable than carbide-
argue that you can do without a circular saw. But
tipped blades.
I beg to differ: A nibbler can cut across a plank,
Electric or pneumatic shears are another must- but a circular saw is faster and yields a cleaner
have tool for cutting curves or inside corners in
edge. For those not siding a whole house, the
fiber-cement siding. Because shears (also called
Malco TurboShear™ attachment converts most
drill/drivers into FC shears for about half the cost
of dedicated shears.
A pneumatic coil nailer designed for fiber
nibbling iN thE Air cement is a big-ticket item, but it’s worth the
money on a whole-house job. This nailer is also a
acircularsawproducesthecleanestcutsina
great asset when working with fiber cement:
fiber-cementplank.butsometimesitismore
Once you’ve established the correct air pressure,
convenienttouseacordlessnibbler.Forexam-
you’re unlikely to crack this brittle siding.
ple,ifyou’reworkingundertheeaves,notching
Moreover, although predrilling is recommended
aroundrafters,ormakinglong,triangularcuts
when you’re hand-nailing FC siding, that’s not
inraketrim,abattery-powerednibblerisper-
necessary when pneumatic-nailing if the air pres-
fect.Smallandportable,ittakesupnoroomon
sure is correct and you place nails far enough
thescaffold.Soyoucanmarkandcutboardsin
back from the edge. Pneumatic nailers also have
placeratherthangoingupanddownaladder,
exposure gauges that enable you to quickly posi-
whicheatstimeandriskscrackingFCboards.
tion siding courses before nailing them up, much
as roofers set shingle courses (see p. 79).
172 Chapter 7
Miscellaneous tools include carbide-tooth hole
saws for dryer-vent or electrical-box cutouts and
a carbide scoring knife or hand snips for inciden-
tal cuts when you don’t feel like going back down
zzzzzz Stucco Details
Casing bead
the ladder to get your shears. You should also have
an N95 NIOSH-certified respirator whenever
Lath (either wire
you’re using power tools with FC siding.
mesh or expanded
metal)
Stucco Repairs
Two layers Grade D
Stuccoing a whole house requires skills that take
building paper
years to learn, but stucco repairs are well within
the ken of a diligent novice. If you spend a few
hours watching a stucco job in your neighbor-
Solid sheathing
hood, you’ll pick up useful pointers.
A BASIC DESCRIPtIOn
Stucco is a cementitious mix applied in several
layers to a wire-lath base over wood-frame con-
struction or to a masonry surface such as brick,
Three-coat stucco
block, or structural tile. Like plaster, stucco is
usually applied in three coats: (1) a base (or
scratch) coat approximately 1⁄2 in. thick, scored
horizontally to help the next coat adhere; (2) a
brown coat about 3⁄4 in. thick; and (3) a finish
Weep screed allows
coat (called a dash coat by old-timers) 1⁄
water to drip free.
8 in. to
1⁄4 in. thick. For repair work and masonry-
substrate work, two-coat stucco is common.
the mix. The mix always contains portland
cement and sand, but it varies according to the
amount of lime, pigment, bonders, and other
Stucco Mixes
agents. See “Stucco Mixes” at right, for standard
mixes. The consistency of a mix is easy to recog-
PoRTLandCEMEnT
MaSonRyCEMEnT
LiME
Sand
nize but hard to describe. When you cut it with a
1 part
—
1⁄4 to 1 part
31⁄4 to 4 parts
shovel or a trowel, it should be stiff enough to
retain the cut mark yet loose enough so it slumps
1 part
1 part
—
31⁄4 to 4 parts
into a loose patty when dropped from a height of
1 ft. It should never be runny.
Building paper. Stucco is not waterproof. In
fact, unpainted stucco will absorb moisture and
wick it to the building paper or sheathing under-
neath. Always assume that moisture will be pres-
ent under stucco, and apply your building paper
accordingly.
Basically, you want to cover the underlying
sheathing with two layers of building paper before
attaching the metal lath. Two layers of Grade D
building paper will satisfy most codes, but
you’re better off with two layers of a fiberglass-
reinforced paper such as Super Jumbo Tex
60 Minute. Although 60-minute paper costs
more, it’s far more durable. Typically, the stucco
sticks to the first layer of paper, exposing it to
repeated soakings until it largely disintegrates;
the second layer is really the only water-resistant
The perfect stucco mix is stiff enough to retain a trowel mark yet loose enough
one, so you want it to be as durable as possible.
to slump into a loose patty when dropped from a height of 1 ft. This mason is
using his trowel to load stucco mix onto his hawk, which he’ll carry to the wall.
With a trowel, he’ll apply the mix in sweeping motions.
Exteriors
173
Take care not to tear the existing paper around 8-ft. sheets, is somewhat more work to install,
the edges of a patch. Tuck the new paper under
and costs more. Expanded metal lath is stapled
the old at the top of the patch, overlapping old
or nailed up; there’s no need for furring nails
paper at the sides and bottom of the patch. If
because it’s self-furring.
P R O T I P
the old paper is not intact or the shape of the
Base coat. Here’s how to apply the base
patch precludes an easy fit, use pieces of polymer- (scratch) coat:
Don’t use plastic housewrap as
reinforced flashing strips as “shingles,” slipping
a membrane beneath stucco.
1.Cover the sheathing with building paper and
them up and under the existing stucco and paper
Stucco that comes into contact
attach the lath.
and over the new. Caulk new paper to old at the
with housewrap will bond to the
edges to help keep water out.
2.Establish screed strips, which are guides for
surface, filling its pores and
the stucco’s final surface thickness. Screeds can
allowing water to pass through
lath. Metal lath reinforces stucco so it’s less likely
via capillary action. Stucco also
be existing window edges, corner boards, or
to crack and also mechanically ties the stucco
contains surfactants (surface-
strips manufactured for this purpose.
to the building. Lath is a general term; it encom-
active substances) that reduce
passes wire mesh or stucco netting (which looks
3.Mix and trowel on a thick first coat, press-
the water-shedding qualities
like chicken wire) and expanded metal lath
ing it to the lath.
of housewrap.
(heavy, wavy-textured sheets). When nailing up
4.When the mud has set somewhat, screed it
wire mesh, use galvanized furring nails with a
(meaning get it to a relatively uniform thickness)
furring “button” that goes under the mesh. When using screed strips as thickness guides.
you drive these nails in, you pinch the wire mesh
between the nail head and the button, creating a
5.Even out the surface further with a wood- or
space behind the mesh into which the scratch
rubber-surfaced float.
coat oozes, hardens, and keys. Don’t use alumi-
6.Press your fingertips lightly against the sur-
num nails because cement corrodes them. Use
face; when it is dry enough that your fingers no
about 20 nails or staples per square yard of lath,
longer sink in, steel-trowel the surface. Steel
spacing nails at least every 6 in. Overlap mesh at
troweling compacts the material, setting it well in
least 2 in. on vertical joints, and extend it around the lath and driving out air pockets.
corners at least 6 in.
7.Scratch the surface horizontally.
Expanded metal lath is a thicker, stronger lath
used in situations requiring greater strength—for Brown coat. Installing the brown (second) coat
example, to cover soffits, where you’re fighting
requires the most skill, care, and time because
gravity while applying stucco. That is, expanded
this stage flattens the surface and builds up the
metal lath won’t sag. It typically comes in 2-ft. by stucco to within 1⁄8 in. of its final thickness.
Applying the brown (second) coat takes a lot of skill.
The mason starts with an irregular scratch coat and
builds it up until the surface is flat and within 1⁄8 in.
of its final thickness.
After applying the rough, brown coat with a hand trowel,
the mason steel-trowels the surface to make the thickness
uniform and the surface relatively flat. After the mortar
sets, he’ll rough up the surface slightly with a wood- or
rubber-faced float.
174 Chapter 7
hElPFul MAtERIAlS
Diagnosing stuCCO The following materials are particularly useful
PrOBlEMs
for repair work and are available from any
masonry supplier.
Herearesomecommonsymptomsofstucco
Weep screed is a metal strip nailed to the
problemsandtheirprobablecauses.
base of exterior walls, providing a straight
diaGonaLCRaCkSfromthecornersofdoor
edge to which you can screed stucco. Because
orwindowtrimindicateashiftingfoundation;
it is perforated, it allows moisture to “weep,”
callastructuralengineer.
or migrate free from the masonry surface, thus
allowing it to dry thoroughly after a rain. Weep
/>
CRUMbLinGSTUCCoalongthebaseofawall
screeds are an easy way to make the bottom
suggestsstandingwaterandprobabledeteriora-
edge of stucco look crisp and clean. And
tionofthesheathing.Cutbackthedamaged
because the weight of the stucco flattens the
areaandinstallaweepscreedsowatercanexit.
screed down against the top of a foundation,
P R O T I P
LaRGEPaTCHESFaLLinGoFFsuggestfaulty
the screed provides a positive seal against
flashing,rottedsheathing,orlaththat’sinsuf-
termites and other pests. (Stucco’s tendency
two ways
ficientlyattached. Note:ifyouseeashiny
to reduce stucco
to retain moisture makes rot and insect infest-
shrinkage cracks: (1) Add nylon
surfacebeneathasectionofstuccothatfelloff,
ation particular problems.) Weep screed is
fiber to the scratch coat. (2)
theinstallerlikelywaitedtoolongtoapplythat
also a good solution for the frequently rotted
After the top stucco coat has
coat,mistakenlylettingthebonderdry.inthis
intersection of stucco walls and porch floors.
cured at least three weeks, paint
case,roughenthesurfacewithachiselbefore
Weep screed isn’t difficult to retrofit, but
it with an elastomeric paint,
applyingnewbonderandastuccopatch.
you’ll need to cut away the base of walls 6 in.
which flexes as materials expand
to 9 in. high to flash the upper edge of the
and contract.
screed strip properly. Cut the screed with
aviation snips, and fasten it with large-head
8d galvanized nails.
To apply the brown coat, trowel on the stucco,
Wire corners are preformed corners
screed it to a relatively uniform thickness, float
(also called corner aids) that can be fastened
the surface further, and steel-trowel to improve
loosely over the wire lath with 6d galvanized
the uniformity. Then roughen the surface slightly nails. Set the corner to the finished edge,
with a wood or rubber float. As the stucco sets
taking care to keep the line straight and either
up, you will be able to work it more vigorously
plumb or level.
to achieve an even, sanded texture that will
Latex bonders resemble white wood glue.
allow the finish texture coat to grab and bond.
They are either painted into areas to be
Do not leave the brown coat with a smooth, hard- patched or mixed into batches of stucco and
Renovation 4th Edition Page 40
