Wides. Use a small sledgehammer and chisel to undercut the edges of the. Undercutting the makes it wider at the base than at the surface, providing a mechanical method of “keying” the patch in place for a more secure and permanent repair. Clean the area in and around the with a wire brush and broom..Slab is a water based acrylic latex caulk for concrete repair. Unlike other concrete repair products, it’s not sticky and difficult to apply, nor does it dry hard and. Slab combines excellent adhesion and superior elasticity to result in a concrete repair that lasts..The experts at DIYNetwork.com show how to repair concretes with easy to follow, step by step instructions. Any DIYer can repair concrete, giving it longer life and a better appearance..Concrete Slab Repair How to repair a badlyed concrete patio slab with Emecole for a permanent structural bond..