First of all, unless the existing substrate (such as a formica countertop) is no longer viable, or the sink placement is changing, there is probably no reason to rip out the old countertop. KreteKraft can install the new look right over the old countertop. This reduces cost, and keeps some garbage out of the landfills.
But in the case of new construction, when the existing substrate is no longer structural, or when the sink is being moved or resized for instance, a new substrate is needed.
The best material for a new substrate is MDF (medium-density fiberboard) which is available from most home improvement stores. (Be sure to wear a dust mask when working with any substrate material, and MDF is no exception.)
For a typical countertop thickness of 1.5 inches, we suggest two layers of 3/4 inch material. The top sheet should be glued and screwed to the bottom sheet. Be sure to countersink the screws so that the head is slightly lower than the surface. Screws should be placed every 4 inches, including around all the edges, even the back edge. This will ensure that the two sheets act like one. Make sure that the substrate is tight against the wall with no gaps greater than 1/4 inch.
There are two ways to get the overhang you want. The first is to simply cut the MDF to include the overhang. As long as the screw and glue instructions above are followed this will work fine. The other option is to attach a 1x2 furring strip around the edges. This should also be screwed and glued, and it helps to pre-drill the attachment holes so you don't split the lumber.
It should be noted that some very interesting looks can be achieved with even wider edge material on breakfast bars and such. This gives the look of an enormous piece of rock!
We suggest that the substrate be attached from underneath the cabinet into the bottom of the substrate rather than from above. This is standard practice for the pros, but sometimes homeowners miss this, and it makes it impossible to remove the countertop in the future without destroying the finish layers. Oops!
We will provide you or your contractor specifications that articulate the above in writing for cases where a new substrate is required. It's not hard to do, nor is it costly.
If you would prefer for KreteKraft to provide the new substrate, we will be happy to coordinate with one of our preferred contractors.
Depending on the location, size, and cabinet style, additional reinforcing may be required. KreteKraft can provide some additional information and tips for your specific situation.