Hang the Board
The Durock we use is the same cement-based product tile
installers use on floors and walls under ceramic tile.
Typically, we score and snap the panels using standard drywall
or utility knives with a heavy-duty blade or carbide scoring
tip; for crisp edges, we cut it with a circular saw equipped
with either a dry diamond or carbide blade. (We’ve tried
using standard masonry "mesh" type blades, but they don’t
last.) Sawing creates a lot of dust, so dust masks are standard
equipment for the crew.
We use 4x8 sheets for the first two courses, which we can
reach from the ground, and 32-inch-wide sheets for everything
higher (Figure 8).
8. With the drainage plane and scaffolding in
place (top left), the Durock cement board panels are
applied in a staggered pattern (top right). Spaces
between panels provide a keyway for the stucco. A vinyl
starter bead maintains a clean reveal along the exposed
bottom edge of the cement board (left).
It generally takes two men to handle a 4x8 sheet, plus an
additional man per level of scaffolding to pass it up. The
smaller panels can be managed by one man.
Durock installation begins with a starter track, a vinyl
accessory with weep holes that allow water to escape from the
bottom. Starter track is optional at the base flashing, but we
use it to ensure a clean line at the bottom of the Durock. We
use a water level to make a level line at the foundation and
check the concrete or block for stray mortar and any other
obstructions. Then we nail the track using 11/4-inch hot-dipped
galvanized roofing nails.
We seat the first course into the starter track
perpendicular to the framing, taking care not to distort the
track or block the drain holes. We use nails to space sheets
both horizontally and vertically, creating a 1/16-inch
mechanical key like with plaster systems.
We use hot-dipped galvanized roofing nails to attach the
cementboard and all the accessory channels. We tried the
special Durock screws, but found them difficult to use. We
follow the recommended fastening pattern and stagger the butt
joints as we go. As with drywall, we avoid seams at door and
window jambs; instead, we run sheets past the top and bottom of
the openings by 6 to 12 inches.
To accommodate expansion and contraction, the Durock layer
is divided into sections with 3/4-inch-wide control joints that
are filled with foam backer rod and caulking. Many homeowners
and building designers object to the obvious spaces, which are
visible from the street, but they are necessary evils of this
system. The effect can be minimized, however, with
At floor framing lines and at the intersection of dissimilar
materials, we use either a vinyl casing bead or L-bead. At the
heads of windows and doors, we use a vinyl drip flashing. The
edges of openings receive either a 45-degree bead or a casing
bead. Any non-reactive metal would work for these flashings,
but we typically stick to the vinyl flashings that come with
the system to avoid any galvanic reactions with the Portland
cement in the base coat, like you would get with aluminum or
On this house, as is true with many houses using a synthetic
stucco system, most openings called for built-up foam detailing
9. Hand-carved foam details are common in synthetic
stucco systems (left). For extra durability, the foam trim is
either bedded in mesh tape or capped with vinyl beads, as shown
To strengthen these foam details, the system calls for
either applying trim bead along the edges or "back-wrapping"
the foam using an exterior-grade fiber mesh. For typical
rectangular foam details, the mesh is cut wide enough
so that it extends 2 inches under the trim, wraps completely
around the three exposed faces, and then extends 2 inches onto
the face of the Durock. It’s left loose on the face of
the foam buildup until the base coat is applied, at which time
it will be embedded in the base coat.