Page 262 - Construction Waterproofing Handbook

SEALANTS 5.21
● Adhesion strength
● Cohesion strength
● Elasticity
● Expected life
● Modulus
Additional desirable features or charac-
teristics include color, availability,
paintability, substrate compatibility, ultravi-
olet resistance, and presence of one or two
component materials.

Elongation
Elongation is the ability of sealants to
increase in length, then return to their
original size. Limits of elongation are
expressed as a percentage of original size.
A material with a 200 percent elongation
ability is, therefore, capable of stretching
to double its original size without splitting
or tearing. Since this is an ultimate mea-
sure of failure, joints are not designed to
perform to this limit of elongation, rather
to a portion of this capability including a
safety factor consideration. A joint
stretched to its limit will not return to its
original shape or size. Thus, a joint will
FIGURE 5.27 Envelope-joint construction for cease to function properly if elongated to
effective sealing. its maximum elongation capability.

Modulus of elasticity
The modulus of elasticity is the ratio of stress to strain and is measured as tensile strength,
expressed as a given percentage of elongation in pounds per square inch. Modulus has a
direct effect on elongation or movement capability. Low-modulus (tensile strength under
2
60 lb/in ) materials have a higher ability to stretch than high-modulus sealants. High ten-
sile strength results in lower movement capability. More simply, soft materials are more
easily stretched than harder materials. Low-modulus sealants with high-elongation factors
are required in high-movement joints.
Elasticity
Elasticity and recovery properties are measures of a sealant’s ability to return to its origi-
nal shape and size after being compressed or elongated. As with elongation, elasticity is
measured as a percentage of its original length. In high-movement joints, a sealant with
sufficient recovery ability is mandatory. A sealant that does not continually return to its
original shape after movement will eventually fail.