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I recently repaired two granite countertops that had failed reinforcing rods at the kitchen sink cutout. One was an Uba Tuba top, and the other was a Bordeaux top. In each case, the cause was a compounding of failures rather than just a single problem: Latex caulk was used instead of silicone between the undermount stainless steel sink flange and the underside of the granite; particle-board scraps glued with polyester adhesive were used to support the flange of the undermount sinks instead of a Hercules Universal Sink Harness from Braxton-Bragg (braxton-bragg.com); and plain steel rods, instead of stainless or fiberglass ones, were embedded in the granite with polyester adhesive instead of epoxy, the material recommended by the Marble Institute of America.
Water from activity in and around the sink had leaked past the failed caulk and ponded on the sink flange until the granite absorbed it. It passed through the polyester adhesive to the steel reinforcing rod, causing the rod to rust and expand, which cracked the granite.