Page 196 - Handbook of Adhesives and Sealants

166 Chapter Four

Figure 4.19 ASTM C 719 test method for measuring adhesion and cohesion of elasto-
meric joint sealants under cyclic movement. 19
is a quick and easy way to determine adhesion either in the laboratory
or at a job site. Minimum values of 5 piw are considered satisfactory
in ASTM C 920.

4.5.3 Tear strength
The tear strength of a sealant is important because often the sealant
must resist abrasion. Abrasion can come from outside sources, such
as automobile tires continually running over a concrete sealant. Ab-
rasion can also come from internal sources, such as when dirt particles
become trapped in the sealant and then cause abrasion each time the
sealant goes through an expansion-contraction cycle.
Tear strength is measured by ASTM D 624. This is a general mea-
sure of the toughness and abrasion resistance of the sealant. However,
one can also get a general idea of the tear strength of a sealant by
simply scraping at it with a fingernail.