Many homeowners using slab counters of granite, marble, and quartz in their kitchens also use these materials on breakfast bars and other seating areas. To make room for the chairs and the person seated there, the countertop needs to extend outward a certain amount past the cabinets or knee wall. Because granite and marble are stone and naturally hard and durable, homeowners may consider extending the counter well past the point of stability, where the stone could begin to bend or break.
Most stone for countertops is sold in either 2cm or 3cm thicknesses. No 2cm counters should be extended past 6- to 8-inches without being reinforced with a steel plate below the stone, or with corbels coming off the counter to add support.
3cm and thicker counters may be able to be extended 12-inches or more past the cabinets without support, but this depends largely on the stone. Very hard Class A stones such as Absolute Black can be extended 12 or more inches without issues. Some Class C and D stones, however, can’t be extended even 12-inches without eventually beginning to bend or break. In many installations, a level placed on this area of the counter after a few months of use will show that the stone is beginning to bend without the support that it needs.
For homeowners that want to maintain a contemporary look in their kitchen without corbels or visible supports, the stone thickness can be increased for these counters to help support it. Otherwise, a thin sheet of stainless steel can be bolted to the top of the cabinets, extending to within 6-inches of the edge of the counter, and the stone can be installed on top to prevent the eventual bending and cracking of the counter.
For homeowners with formal, Country, and transitional kitchens, corbels or supports built into the cabinets can help prevent the counter from breaking over time.