This is the most important step most DIYers skip. Brush a generous, even coat of concrete bonding adhesive onto all surfaces of the repair area (both the bottom and sides). Follow the manufacturer’s instructions—some require you to apply the patching material while the adhesive is still tacky, others require it to dry first.
Use the wire brush to scrub away all dust, dirt, and small loose particles. For best results, rinse the area with a garden hose and let it dry completely (or use a shop vac). The surface should be clean and slightly damp before applying the bonding agent—not soaking wet. how to repair crumbling concrete window sill
For most homeowners,
Mix your vinyl concrete patcher according to the package directions. Aim for a consistency like stiff peanut butter—it should hold its shape but still be workable. This is the most important step most DIYers skip