Jadestone Architects on Instagram: "Undermount Sink Installation Guide | Step by Step Kitchen Sink Fitting Tutorial 🔧” Installing an undermount sink during your kitchen renovation? If not done correctly, you’ll face water leakage, visible joints, and countertop damage. Here’s the professional way to install it for a seamless, durable, and modern kitchen design: Step 1 – Plywood Cutting: Take the exact measurement of the inner top of the kitchen sink bowl and cut the same size on plywood.