Page 252 - Construction Waterproofing Handbook

SEALANTS 5.11
OPEN-CELL
BACKER ROD

Open-cell backer rod is manufactured with
polyethylene or polyurethane foam, but its
cell structure remains open to permit vapor
or air transmission. Open-cell rod can easily
be compressed (like foam rubber), making
it readily differentiated from closed-cell
material that is not so compressible.
Open cell is specifically designed for
sealant materials that are moisture- or air-
cured products and not recommended for use
with urethane materials or moisture-sensitive
sealants. Open cell is generally used with low-
FIGURE 5.12 Backer rod is manufactured in fillet
shapes for cant type applications. (Courtesy of modulus, slow-curing, high-performance
Nomaco) sealant materials. Moisture curing is only
applicable with airborne moisture and not
with visible standing moisture that deteriorates sealant material. The open-cell material pro-
motes curing on both sides of the joint and should be used whenever double seal joints are
required to facilitate proper curing of all joint faces.
Open-cell rod is not generally used on horizontal joints, due to the probability of mois-
ture accumulating in the joint before and immediately after sealant application that can
cause the material not to cure properly. Open cell was developed to eliminate the problems
associated with gassing of the joint as described above. However, the resulting open-cell
structure permits moisture entrapment that can equally destroy sealant materials. Open-
cell materials are typically not compatible with EIFS systems; when installing EIFS sys-
tems, the manufacturer should provide specific recommendations for sealants and the
required backing materials.

1
1
TABLE 5.2 Typical Sizes of /4 and /2 Round Backer Rod Available. (Courtesy of Nomaco)
HBR® 1 4 AND 2 ROUND AVAILABLE
1
SIZES
1 4 ROUND 1 2 ROUND
A B A B
Dimension in.—mm Dimension in.—mm Dimension in.—mm Dimension in.—mm
1 1 5 5
4 6 4 6 8 16 16 8
3 3 3 3
8 10 8 10 4 19 8 10
1 1 1
2 13 2 13 1 25 2 13
3 3 1 5
4 19 4 19 1 4 32 8 16
1
1 25 1 25 1 2 38 3 4 19
1 1
1 4 32 1 4 32 2 51 1 25
1 1 1 1
1 2 51 1 2 51 2 2 38 1 4 32
1
2 51 2 51 3 51 1 2 38