Page 67 - Handbook of Adhesives and Sealants

An Introduction to Adhesives and Sealants 35

that it does not adhere to all surfaces. To achieve this affect, a bond-
breaker or release material at the bottom of the joint is generally used,
as shown in Fig. 1.9.
Conditions that will influence the adhesion of sealants include water
exposure, temperature extremes, movement considerations, and sur-
face cleanliness. Often a surface conditioning process or a priming step
is necessary to make a substrate compatible with a specific sealant.

1.5.3 Design considerations
When working with sealants, concerns such as crack bridging, cover-
age rates, color, practicality of placement, order of placement, unusual
movement conditions, and aesthetics must be addressed. One consid-
eration that is required of sealants and not generally with adhesives
is appearance. A sealant material may be acceptable in all respects,
but appearance problems could make it aesthetically unacceptable.
Usually, sealants are easily visible whether the application is in the
automotive, construction, or appliance industries. Adhesives, on the
other hand, are often hidden by the substrates. The sealant material
could also contain compounds that discolor surrounding areas. They

Sealant

Release Tape

Joint Movement

Figure 1.9 Corner sealant joint showing release tape. 11