Page 264 - Construction Waterproofing Handbook
P. 264
SEALANTS 5.23
Cohesive failure is when a sealant tears or splits apart due to excessive joint move-
ment or improper installation (Fig. 5.29). Excessive movement failure occurs whenever
the material selected does not have the movement capability of expected life-cycle
movement or if the joint is designed too small to handle the actual movement that
occurs.
Installation problems that facilitate cohesive failure include the sealant being applied
too thickly to permit proper movement at the joint. Also, not properly installing the sealant
in the “hourglass” shape will often result in cohesive failures.
Shore hardness
Shore hardness is resistance to impact, measured by a durometer gage. This property
becomes important in choosing sealants subject to punctures or traffic, such as horizontal
paver joints. A hardness of 25 is similar to a soft eraser; a hardness of 90 is equivalent to
a rubber mallet.
FIGURE 5.29 Cohesive failure of sealant; exceeds three inches. (Courtesy of
Coastal Construction Products)
