Using a Resilient vs. Rigid Seam Filler
What’s the best way to fill the seams in precast countertops?
We recommend using a resilient caulk to fill seams in precast concrete countertops, such as a siliconized latex acrylic caulk or 100% silicone caulk, in a color that coordinates with or matches the countertop color. Another option is to use a rigid epoxy filler. Although epoxy-filled seams sometimes look better, they do not provide the stress isolation that resilient caulk-filled seams do.
Seams in precast countertops are control joints, allowing adjacent slabs to move or deflect due to structural movement of the house and cabinets (often driven by seasonal humidity changes or simply due to settlement of a new structure). A resilient seam filler allows movement without stressing the concrete. A rigid epoxy filler, on the other hand, may actually be too strong and rigid in some cases. Because the ends of abutting slabs are glued together with epoxy, any flexure or deflection is transferred across the joint, causing tension and compression in the concrete. But since the countertop reinforcement is not continuous across the joint, any tension forces are resisted by the concrete alone. The common result is a crack that forms immediately adjacent to and parallel with the epoxy joint.