Page 283 - Construction Waterproofing Handbook

5.42 CHAPTER FIVE

FIGURE 5.38 Typical bulk gun sealant applicator tool. (Courtesy Albion
Engineering Co.)

underfilled if proper nozzles are not used, causing tooling problems, improper depth-to-
width ratios, and adhesions problems. Figure 5.40 shows the proper placement of a nozzle
while sealing.
Joints must be tooled to eliminate voids or bubbles and to ensure that the materials press
completely against the sides of joints. Joints are tooled in a concave finish as shown in
Fig. 5.41. This hourglass structure allows material to move properly and enhances the
physical properties of a sealant.
Many types and sizes of tools are available for joint finishing, including those required
for recessed joints. Soaps or solvents should never be used in tooling a joint because they
will cause improper curing, adhesion failure, or color change (Fig. 5.42).
Proper mixing, application, and tooling of sealants includes:
● Applying only in recommended temperature ranges, typically 50–80°F
● Mixing only complete packages of materials
● Using the appropriate mixing equipment
● Mixing for the proper amount of time
● Keeping air out of sealant during mixing
● Using properly sized nozzles and slopes to fill joints
● Tooling joints by compression, for adequate adhesion
● Avoiding use of soaps or solvents in finishing joints

When the hourglass shape, as described previously, is not properly created, failures
often occur because the sealant is either too thick or thin to function as intended and test-
ed. Sealants that are applied too thick, often when the backer rod is installed too deep into
prepared joint, will promote cohesion failure.
Cohesion failure results when the sealant is so thick that it can not elongate when the
substrate is experiencing expansion movement. The sealant literally rips itself apart, usu-
ally in the middle of the joint, when the substrate separates. This is reflected in Fig. 5.43.
Likewise when the sealant is installed in too thin an hourglass shape, again often due to
misplacement of the backer material, the joint will likely fail in an adhesive manner.
Adhesive failures occur when there is insufficient sealant material adjacent on the sides of
the substrate to permit proper movement in the expansion mode. When the substrate moves
apart the sealant is ripped off the side or sides of the joint, due to insufficient bonding