Levelling and Why Cabinets Are Shimmed First
The Base Is the Structure
A worktop does not span between cabinets in any engineered sense. It rests on them, and it transfers everything it carries straight down through whatever is underneath. That makes the cabinet run the structural element and the stone the finish, which is the reverse of how most people picture it.
What Is Actually Measured
A long straight edge and a spirit level along the front of the run, across the depth at intervals, and diagonally on an island. The crew is looking for deviation from a plane, not for absolute level. A run that is uniformly two millimetres low at one end is fine. Two millimetres of dip in the middle of a span is not.
Shims, Packers and Where They Go
Correction happens at the cabinet feet where there is adjustment, and with thin packers on the top rail where there is not. Packers must sit under a load path, which means over a side panel or a rail, never floating in the middle of an unsupported top edge. A packer in the wrong place moves the problem rather than fixing it.
Old Floors Complicate It
In a house with a settled timber floor the cabinet feet may already be at the end of their adjustment before the run is flat. At that point the honest answer is packing under the carcass, which is a joinery job, not something to be absorbed by the worktop installer on the morning. It is worth checking during the template visit.
The Substrate Question
Thinner materials and some engineered surfaces are fitted onto a continuous ply or batten substrate rather than directly onto rails. Where that is specified, the substrate has to be flat too, and it has to be fixed down. A substrate that is itself following a dipped cabinet run has achieved nothing.
Why Rushing Here Costs Later
Every hour spent levelling is invisible in the finished kitchen, which is why it is the first thing compressed when a schedule slips. The failures it prevents are also invisible until they are not: a cracked cutout corner, a seam that opens, a sink that pulls away. None of those are repairable to as-new.