Page 244 - Construction Waterproofing Handbook

SEALANTS 5.3
● Glass
● Plastics, including acrylics, waterproofing sheet goods, PVC, fiberglass
● Substrate finishes such as fluoropolymers on aluminum, paints, primers, and admixtures
● Roofing and waterproofing products
Each of these substrates must be reviewed and an appropriate sealant chosen to facili-
tate closure of the building envelope and effective watertightness. Contrary to popular
belief, there is no one sealant for every purpose. Many substrates require primers before
sealing; therefore, it is imperative that the sealant manufacturer be consulted to confirm
that the substrate is acceptable for use with the specified product; and in addition, if needed,
what type of primer is required to guarantee adhesion.
Actual selection of a sealant product is one of many important steps required to ensure
successful installations, including:
● Joint design
● Material selection
● Substrate preparation
● Joint preparation and installation

Each step is critical for sealant systems to perform successfully for extended periods of
time. Better sealant materials will perform for 5–10 years. But because of improper design,
incorrect material choices, poor installation, or a combination of these factors, sealant
joints rarely function within these time parameters.

JOINT DESIGN

Joint design failures are often attributable to improper spacing and sizing of joints. Joints
are frequently arranged for aesthetic purposes, and actual calculations to determine opti-
mum number and spacing of joints are overlooked. Precast and prefabricated panel joints
are often determined by panel size of an individual precast manufacturer rather then by
sound joint design.
Even if joint size requirements are actually determined, far too often panel erectors are
primarily concerned with the installation of panels, with joints being used to absorb instal-
lation tolerance during erection. Often these joints end up varying greatly in width from
those originally intended, with no procedures followed for maintaining proper tolerance in
joint width.

Joint type
The first step in proper joint design is to determine areas and joint locations required
within a building envelope. Areas of change in materials (e.g., from brick to concrete), of
changes in plane, of differential movement potential (e.g., spandrel beams meeting
columns), of protrusions (e.g., plumbing and ventilation equipment), and of thermal move-
ment all must be studied to determine location requirements for joints.