Before any renovation project, check the foundation walls to ensure there is no indication of deterioration of the concrete such as spalling – that is, where pieces of concrete have broken off the wall to reveal the reinforcing, which can then rust.
If minor spalling has occurred, it can be repaired in the following process:
- Chip out the edges of the spalled area removing all dirt, laitance, and loose or deteriorated concrete.
- Any reinforcing steel that is exposed should be treated with a rust prevention product before the concrete repair mortar is placed.
- Thoroughly saturate the concrete before placing new material.
- Prepare a concrete repair mortar with a bonding agent added.
- Apply the mortar to the saturated concrete and and brush finish to match existing concrete.
- Ensure that the patched concrete does not dry out too quickly by covering with a damp cloth or by keeping a sprinkler on it for a few days.
If the spalling is more severe, apply a bonding slurry consisting of a 1:1 cement/fine sand mix with a bonding agent added, in a layer that is no more than 3 mm thick, to the cleaned, saturated surface of the concrete before applying the repair mortar. If the spalling is extremely severe, the section of the wall may need to be replaced. Call in an experienced engineer or specialist repair contract to advise.