shear capacity and rigidity of the
anchors. The rigidity may be partially
overcome by using 1/2-inch-long
compressible (60 durometer) rubber or
elastomeric grommets or sleeves on the
anchor at the back surface of the stone,
as seen in Fig. 7.
Differential thermal expansion of the
stone and unfilled epoxy may cause
cracking of the stone veneer. The
coefficient of expansion of epoxy and stone
should closely match. It may be more desirable to fill the anchor hole with a low modulus polyurethane
sealant. The overall effect of either epoxy or sealant materials on the behavior of the entire veneer should
be evaluated prior to their use. At best, the long-term service of epoxy is questionable, so any increase in
shear value should not be used in calculating long-term anchor capacity.
The stone trade associations and the suppliers of different kinds of building stones recommend safety
factors. Because of the expected variation in the physical properties of natural stones and the effects
of weathering, recommended safety factors are larger than those used for manufactured building
materials, such as steel and concrete. The minimum recommended safety factor, based on the average
of the test results, is 4 for anchorage components. If the range of test values exceeds the average by
more than ±20 percent, then the safety factor should be applied to the lower bound value. (See Appendix
to ASTM C1242 for a discussion on safety factors.)
Finite-element analysis is a useful technique for
evaluating stress in a veneer panel system. This
necessitates testing to determine the spring constant
values for the panel’s material components to model the
assembly. Stone veneer should be tested in flexure, (ASTM
C1352). The section properties and modulus of elasticity
also should be determined. Granite rift (bedding) planes,
direction and grain size influence modulus of elasticity. Shear
and tensile tests are required for the anchors. The spring
constant of a compressible bondbreaker should be determined.
For insulation, compressive-spring and shear-spring constants
should be determined if no bondbreaker is used
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