Page 265 - Construction Waterproofing Handbook

5.24 CHAPTER FIVE
MATERIAL TESTING

All of the properties discussed must perform in unison for materials to function as neces-
sary during joint life-cycling. Weathering, ultraviolet resistance, amount of movement, and
temperature change all affect sealant durability.
Many tests are available for comparison of different materials as well as different man-
ufacturers. Unbiased testing is completed by the National Bureau of Standards (federal
specifications) and the American Society for Testing and Materials. Tests presently used as
standards include:

● ASTMC-920 for elastomeric joint sealants
● Federal specification TT-S-227 for two-component sealants
● Federal specification TT-S-00230C for one-component sealants
● Federal specification TT-S-001543 for silicone sealants
The ASTM C-920 involves a series of tests including adhesion-in-peel, effects of accel-
erated weathering, indentation hardness, and adhesion and cohesion testing under life-
cycling movement. Whenever this ASTM specification is referred to, the specific test the
manufacturer actually included should be detailed in the product literature.
While these standard tests provide a basis to compare the properties of different manu-
factured products, there are serious flaws that are created when using test results only for
selection of sealants for any specific project. Reference to ASTM C-920, while now widely
referred to in the industry, can be easily abused by manufacturers. This ASTM test is made
sufficiently basic to include a wide range of generic sealant types including single- and
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multicomponent products, traffic- and nontraffic-bearing sealants and 25 or 12 2 percent
joint movement capability. This generality leaves a considerable amount of space for man-
ufacturers to only test a product to a specific test it knows the sealant will pass, and omit
the nonpassing grades from its product literature.
It is also important to recognize that these tests are conducted in a very controlled envi-
ronment of pristine laboratory conditions that are rarely if ever duplicated in actual field appli-
cation conditions. For example, ASTM C-920 requires that the testing be completed in the
ideal conditions of 73.4°F, with a plus or minus of only 3.6°F. In addition the humidity must
remain at 50 percent plus or minus only 5 percent during the entire test and curing stage. These
conditions would rarely be duplicated during the application of any sealant in the field.
The test allows sufficient latitude in how the sealant can be considered to pass. Primers
can be used or omitted at the descretion of the manufacturer, and such details are often not
referred to in the manufacturer product literature. The test also permits a loss of complete
adhesion in a limited area, yet still be considered to pass. In addition, the specification also
permits manufacturers to request specific waivers or exclusions (e.g., longer curing time
before adhesion test is conducted) and not clarify this fact in their product literature.
Therefore it is imperative that whenever considering sealant for a project, a sufficient
safety factor should be incorporated into the design rather than depending solely on the per-
formance during these pristine and perfect conditions of a laboratory test. For instance, a
sealant should have a minimum of 100 percent expected joint movement capability rather
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than the 22 2 or 25 percent tested for in C-920 (this results in a safety factor of at least 4).
Fortunately, most sealants produced today are far superior in performance to the minimum
standards produced by ASTM testing. However, proper selection of sealants for a required