What are the Standards for the Fabrication and Installation of Stone Countertops?


What is the industry standard in regards to seam placement for granite countertops in the kitchen? I just bought a new construction house 4 weeks before its completion. I paid to upgrade builder grade countertops to granite. I was not told that the countertops would be seamed in the front and the back of the sink. I’ve been told by several other granite companies that granite should not be seamed less than 6 inches from a water source unless there are “extreme” circumstances and the buyer is made aware of the seam placement beforehand. What is the correct way?


ANSWER - There is no mandate on where seams can or cannot be placed on a stone countertop, although the standards do state that the layout of the joinery of the countertops is extremely important to the overall appearance.

Layout of joints/seams can be driven by the size and type of stone being used.

The Natural Stone Institute's Dimension Stone Design Manual shows in their Drawing 17-D-1 where the seams near a kitchen sink are in front and back of the sink on both the right side and the left side of the sink.  The drawing notes that there should not be any seams in the countertop over the dishwasher area. They do recommend installing stainless steel reinforcement washers embedded in a resin at each of the front and back joints at the sink.

The span between supports for 3/4" (20 mm) thick stone is limited to 2 feet and 3 feet for 1-/14" (30 mm) stone.  Stone cantilevered beyond the supports (overhanging) shall be limited to 6" (150 mm) for 3/4" (20 mm) thick countertops and 10" (250 mm) for 1-1/4" (30 mm) thick countertops.  But never cantilever a a portion of the stone that represents more than 1/3 the width of the countertop.  Otherwise use corbelled supports.

Lippage at stone joints should not be more than 1/32" (0.8 mm).

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