We are planning an overhang on our kitchen island and will be using Silestone. I have learned that Silestone can be unsupported for up to 12 inches. If we extend the overhang to 12 inches or more, we will need to add support.

My question is: can you cut grooves into the bottom of Silestone to accommodate a half inch flat bar support? My cabinets are frameless and as such, we will need to create a support structure that lies on top of the cabinet top. In order to keep the Silestone flush with the top of the cabinets, the Silestone must be grooved so that the flat bars can sit inside the grooves, keeping the Silestone even with the top plane of the cabinets. I am hearing mixed opinions on whether you can / should do this.

Any recommendations? Thanks in advance!

Why not notch the tops of the cabinets, and by the way, who will do the calculations required to ensure that the bars and their connections can carry the loads of the overhang? Or else, why not just limit the overhang to 12 inches?

Just how far are you looking to overhang the top? One inch more or 10? Without that information the flat bar answer would be yes and no. Also how well will the island that is supporting this top support it. Typical side walls on cabinets are 1/2" to 3/4" thick. The weight that is placed on them is distributed equally on all sides. Once you begin to place more weight on one side because of the overhang the wood no longer can handle this pressure and the cabinet can begin to warp, twist, and perhaps fail. I know its nuts when you just want to go out a few inches but there are a lot of factors to consider both for safety and to assure that the cabinet will not fail