TM 5-805-6
1. Purpose. This manual provides criteria for the
the sealant; i.e., the sealant will remain bonded to
the substrate and to itself for the expected service
design of building joints and for the selection of
life. Joints open and close as the adjacent materi-
sealants to prevent entry of water, air, dust, light,
or sound through the joints.
als are moved by structural instability, thermal
expansion and contraction or (sometimes) changing
2. Scope. This manual describes joint configura-
moisture content.
tions and the selection and use of sealants, back-
a. Structural movement. The scope of this man-
ing, bond breakers and primers for joints in vari-
ual does not include calculation of movements due
o u s construction materials and in various
to structural loads and moisture changes. How-
environments. Design procedure is limited to joints
ever, the extent of such movements can be used to
between parallel materials and does not include
calculate the joint size and to determine the proper
structural design of joints. This manual supple-
sealant.
ments ASTM C 1193 which covers joint design,
b. Temperature movement. For temperature
sealants, primers, backing and bond breakers, as
changes, joint movement depends on the tempera-
well as the application and tooling of sealants.
ture change and effective length of the adjacent
material from the anchor, i.e., the part of the
3. References. Appendix A contains a list of
material free to move in the direction of the joint.
references used in this manual.
When no anchor exists, the joint should accommo-
date the movement of both adjoining materials.
4. Terms. A joint consists of a space between two
c. Butt and shear joints. Butt joints are designed
or more adjacent materials. The joint is sealed
to allow movement at right angles to the plane of
when filled with a caulking or sealant. The terms
the joint faces. When the plane of movement is
"caulking" and "sealant" are often used inter-
skewed or deflected, shear forces must be consid-
changeably in the construction industry. Techni-
ered in the joint design. A shear joint will hide
cally, a "sealant" is anything that "seals," and
and protect the sealant and will put less strain on
this includes caulking compounds.
the sealant as the joint moves. Shear joints are
a. Caulking. In this manual, the term
difficult to design, prepare, prime, seal, and repair;
"caulking" is limited to oil-and resin-based caulk-
however, a shear joint may move laterally a
ing which hardens as it cures and will accommo-
distance equal to the joint width when an elasto-
date little or no joint movement.
meric sealant is used.
b. Sealants. In contract to caulking, the more
d. Width to depth ratio. The general rule is that
resilient "sealants" are rated to stand joint move-
a joint should be at least twice as wide as it is
ments of 12.5, 25, or 50 percent of the joint width.
deep, and never less than 6 mm ( inch) deep. A
c. The sealant system. A sealant is usually
joint that moves should be wider than it is deep
installed as a system which includes a bond
because the sealant must move to, or away from
breaker or backing, and sometimes requires a
the edges as the joint opens or closes. The effect
primer. The adjacent materials are the substrates
can be seen for joint extension in figure 1 and for
to which the caulking or sealant must adhere. A
joint compression in figure 2. In both cases, joints
bond breaker may be required to prevent the
with the same cross-sectional area and different
sealant from bonding to the bottom of the joint.
width-to-depth ratios each move 13 mm (-inch),
The backing supports the sealant from penetrating
either elongating or compressing the sealant.
too far into the joint and may also act as a bond
(1) In figures 1 and 2, two joints are shown
breaker.
with the same cross-section of 1290 sq. mm. (2
d. Field formed and preformed. Both caulking
square inches). As the joint extends or compresses,
and sealants may be "field-formed" from a liquid
the faces, or outer edges of the sealant, are pulled
or paste, or they may be "preformed" as beads,
in or pushed out by the movement of the sealant.
strips or molded parts. Cure time and pot life of
In either case the faces are elongated. However,
field-formed materials are shortened by increasing
the different width-to-depth ratios produce very
temperatures.
different surface elongations.
5. Joint Movement. Joints must be designed to
(2) Figure 1 shows how a 13 mm ( inch)
extension of a narrow joint elongates the sealant
allow for both cyclical and permanent changes in
surface about 3 times as much as a similar
the length, volume, and plane of building materi-
als abutting the joints. A properly designed joint,
extension in a wide joint.
with an appropriate sealant, will accommodate
(3) The difference is even greater when the
movement of the adjacent (or substrate) building
joint is compressed 13 mm ( inch) as shown in
materials with no loss of adhesion or cohesion of
figure 2. Here the surface elongates about 250
1
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