When re-pouring after a gap, what surface preparation is required to ensure bonding?

• A. Apply the same finishing method as the original pour and skip surface prep.
• B. Roughen or clean the old surface, remove laitance, moisten, and ensure bonding; saw-cut or preformed joints as specified.
• C. Remove all old concrete entirely.
• D. Add extra cement to the surface.

Answer: (B)

Bond between old and new concrete relies on creating a clean, rough, and properly moistened surface so the fresh concrete can mechanically interlock and bond effectively.

Roughen or clean the old surface to expose sound concrete, remove laitance (the weak, sugary surface layer), and keep the surface damp but not standing wet. This ensures the new concrete can grips the substrate and develop a solid bond. Saw-cut or preformed joints should be placed as specified to define the bond line and control cracking, helping the repair transfer loads properly.

If you skip this preparation and simply pour over the old surface or fail to remove laitance, the bond will be poor and the repair is prone to debonding. Removing all old concrete is usually unnecessary for a bonded repair and adding extra cement to the surface doesn’t address the weak surface or enhance bonding.