Types of Joints (galvanized, zinc
alloy, vinyl, anodized aluminum)
- One-piece Joints (control joints)
a. V type one-piece expanded flange
b. J type one-piece expanded flange
c. J type one-piece without expanded flange (AKA Control
Joints)
d. V and J type inside corner expanded flange
- Two-piece Joints (expansion joints)
a. Two-piece male/female #40 type expansion joint.
b. Double casing beads with stretchable membrane flashing.
- Three piece specialty joints.
a. three-piece exterior corners
b. three-piece interior corners
c. three-piece soffit vents
d. three-piece special modifications
Placement Requirements:
The international Building Code (IBC) and most model building
codes reference ASTM C 1063, The Standard Specification
for the Installation of Lathing and Furring to Receive Interior
and Exterior Portland Cement-Based Plaster as the lath installation
specification. C1063 requires that control joints (C1063
makes no differentiation between control and expansion joints,
however I will consider control joints to be one-piece joints
and all two or three-piece joints, including back to back
casing beads to be expansion joints). Generally the industry
uses the terms interchangeably.
ASTM C1063 states that “Control joints shall be formed
by using a single prefabricated member or fabricated by
installing casing beads back to back with a flexible barrier
membrane behind the casing beads. The separation spacing
shall be not less than 1/8 in. or as required by anticipated
thermal exposure range (per author and to accommodate stucco
shrinkage).” It goes on to state that it has to conform
to the previous section that states the following: “Lath
shall not be continuous through control joints but shall
be stopped and tied at each side.”
The specification continues by stating, “Control
(expansion and contraction) joints shall be installed in
walls to delineate areas not more than 144 square feet and
to delineate areas not more than 100 square feet for all
horizontal applications, that is, ceilings, curves, or angle
type structures. The distance between control joints shall
not exceed 18 feet in either direction or a length-to-width
ratio of 2 1/2 to 1. A control joint shall be installed
where the ceiling framing or furring changes direction.”
Finally it states, “A control joint shall be installed
where an expansion joint occurs in the base exterior wall.
Wall or partition height door frames shall be considered
as control joints.” 1 ASTM C1063
While this is a mouthful it covers a lot of territory in
just a few sections of the specification. Control/expansion
joints are considered to be a major part of the stucco installation
and necessary in almost every installation. 144 square feet
translates into an area of 12 foot by 12 foot, which in
the scope of things is a relatively small area in most walls.
I have heard many architects state that they didn’t
like to use control joints because they destroyed the look
of the finished product and give it a chopped up appearance.
While this may be true, it is like a concrete contractor
once said about my driveway. “I would have green cut
grooves in you driveway but I didn’t think you would
want all those cracks.” I responded, “But I
have cracks all over the place and if you had cut them at
least they would have been straight.” The same is
true of stucco; you either plan your crack locations using
a control joint or expansion joint or you take the cracks
where ever they happen in the cementitious membrane. Structural
cracks can be a huge source of water intrusion when they
occur. It is far better to have a bunch of straight and
symmetrical lines than to have random structural cracks
as are shown in some of the accompanying photos.
|
Types of Control Joints and Their General
Uses:
One Piece Control/Expansion Joints:
“V”, “M”, or number 15 types of
this joint are generally considered to be control joints
by the industry. This bead is designed to deal with normal
initial stucco shrinkage during the hydrating and curing
stage of the portland cement stucco (generally exterior)
or gypsum plaster (interior) coats and minor thermal expansion
and contraction. These beads all have expanded flanges for
extra bonding of the bead to the lath below. The other aspect
of these beads that they all have in common is the sloping
angular shape of the downward leg of the “M”
shape. The disadvantage to this shape is that since there
is no chemical bond of the stucco to this leg, if installed
incorrectly a stucco separation crack can result at the
juncture of the stucco to the leg of the bead. This will
be explained further in a later section of this newsletter.
“J”, “XJ” or “Griplock J”
types of control joints with expanded flanges and the narrow
wing control joint with the “J” type shoulder
or nose are all grouped together because of the commonality
of their shoulder shape. They are also considered control
joints and are one-piece joints The advantage to this shape
is that the down turning shoulder bites into the stucco
and as a result the crack described in the above paragraph
is less likely to occur or be exposed. The plasterer must
force stucco under this upside down “J” shape
in order for this bead to perform optimally. These products
are also generally available with a continuous piece of
tape masking over the groove making clean out of the joint
less tedious and more likely to be performed as required.
This requirement will be discussed later in this article.
Two-Piece and Three-Piece Expansion Joints:
Two-piece mechanical male/female sliding expansion joints
are currently manufactured to slide in and out and up and
down allowing them to move in two planes. They also can
move to a larger degree than one-piece joints and therefore
allow for a greater degree of movement at such locations
as through wall expansions. The female should be on the
bottom in horizontal applications and a flexible membrane
should be installed behind the joint to help prevent leakage
that is somewhat common with these beads.
Two-piece expansion joints formed with back to back double
casing beads with a flexible membrane mounted behind the
joint also moves in two planes and when caulked utilizing
backer rod and a quality silicone caulking material it is
generally much more water resistant than the standard mechanical
two piece.
Three-piece joints, though rarely used do have their place
in stucco construction and each should be approached based
on its intended use and application. These would include
such items as inside and outside corners and soffit vent
expansions.
Just How Much Movement Does a Control Joint or
Expansion Joint Control?
These joints deal with minor movement and minor stress
on the stucco membrane. The control joint was designed to
deal with initial stucco shrinkage, minor thermal movement
and some minor stresses imparted on the stucco membrane.
How much movement are we talking about? Not more than 1/32
to 1/8 inch for shrinkage and approximately the same for
all other movement. If it moves more than that due to settlement,
seismic movement, wood shrinkage, or any other reason then
you have the wrong bead. A one piece joint is limited in
the amount of movement it can handle and it can only move
in one plane.
The two and three piece joints are usually employed where
larger amounts of movement that was explained in the preceding
paragraph. The typical two piece can move in two planes,
in and out and up and down and it can be expected to deal
with a grater degree of movement. However, it is not that
much greater but can range from 1/4 inch to just under 1/2
inch. This is a cumulative measurement of closing 1/4 inch
and opening 1/4 inch since it is usually installed in the
already open position of 1/4 to 3/8 inch. Movement of the
sections an additional 1/2 inch would most likely separate
the two sections.
Types of Materials Available for Control/Expansion
Joints:
Control/expansion joints are available in roll formed G60
galvanized steel and zinc alloy (99% pure zinc), extruded
Polyvinyl Chloride (PVC) vinyl and the two-
Expansion/control joints are an essential part of a proper
stucco installation and in the next monthly issue we will
address some of the things that can happen when they are
not used or when they are installed improperly.
|
|
SPONSORS
PHOTOS
Photo 1-B Note the mitered end of the
expansion joint at the junction with the
sloped edge of the foundation weep screed.
Photo 2-B Note the mitered end of the control
joint were it meets the sloped corner bead.
Photo 3-B This photo depicts the junction of
control joints with the casing beads that
surround a window. Note that they slip into
the casing bead because they are !/8 inch
smaller than the casing bead.
Photo 4-B This photo shows a double casing bead used as
an expansion joint. Also, note the junction with the corner
bead.
Photo 5-B Lath that is uncut behind the control joint will
often try to allow expansion. Note the broken strands of
lath.
Photo 6-B ASTM C926 states that control joints must be cleaned
out after the stucco is applied. This joint can’t
function with all of the hardened portland cement in the
joint.
|
