A photo of the actual sink would help.

Probably not quite the same, but I have an undermount sink with an integrated drainboard and the drainboard sits partially over the DW. My counter seam is at the faucet. Counter is 3 cm stone and no additional supports were needed. The whole sink unit is 18" front to back.

With your sink supported by the sink base cabinet and overhanging it 18", your soapstone counter is only cantilevering 6" past the side of the cabinet at the side of the dishwasher. I'm not seeing where any additional support is required.

Not to be downer Dave but how are you going to waterproof where the two counters meet? Are they going to be flush or will the ss counter be over the stone one?

@HALLETT & Co. they would be flush. I was hoping silicone would work. What are your thoughts?

I'd be concerned that being such dissimilar materials they could move really differently. I'm probably still scarred by a client who installed her farmhouse sink 1" above the counter with a giant caulk seam that always failed.

@HALLETT & Co. what kind of motion are you cincerned abiut? Flexing? Differential change in length with temperature?

The metal will expand from the heat of the dishwasher, the stone won’t. The metal may flex slightly from use, the stone won’t. Again no idea if it’s a reasonable concern or not, but when ever two dissimilar materials join it’s something you have to throughly plan

@HALLETT & Co. how much heat do countertops experience from dishwashers, though? Isn’t the DW insulated?

I have a bosch soundproof well insulated dw and my stone counters are very warm to the touch after.

@HALLETT & Co.thanks. We have a terrible Kenmore under 1950s laminate; I dont know if the DW puts out less heat or if it is due to the chipboard and laminate not conducting much heat, but I never realized it could be an issue.