Concrete Repairs on School Window Sills

The problem

We were called in to restore 11 concrete window sills on a school building on Hayling Island, all of which had deteriorated due to corroded reinforcement inside the concrete — a common issue in coastal environments, where salt and moisture penetrate the concrete surface and attack the steel within.

The cause

Window sills sit fully exposed to the weather on every side, which makes them one of the first places coastal corrosion shows up. Once moisture and salt reach the embedded steel, it corrodes and expands, cracking and pushing away the surrounding concrete — exactly the spalling pattern we found across all 11 sills on this building.

What we did

1. Identifying and preparing the repair areas. We inspected the full structure and marked every sill where the concrete had failed, then cut back the damaged sections to clean, square edges — essential preparation so the new repair material bonds securely to sound concrete.
2. Exposing and treating the corroded rebar. All loose and compromised concrete was chipped away to fully expose the corroded reinforcement underneath. The exposed steel was cleaned and coated with a specialist primer, both to stop further corrosion and to help the new repair mix properly adhere.
3. Reinforcement and moulding. Additional Helibar reinforcement was installed alongside the existing rebar to improve durability and crack resistance, then custom timber moulds were built to support each repair area and hold the new material in shape while it cured.
4. Applying the repair mix. The concrete repair mix was built up slowly in controlled layers to avoid slumping, then each sill was trowelled smooth to match the original finish — restoring both function and appearance.

The result

All 11 sills were brought back from heavily deteriorated to fully restored, with the timber formwork and reinforcement work giving each repair the structural integrity to last. This job is a good example of how proper diagnosis and methodical execution can rescue even badly corroded concrete — sills, lintels, or any other structural element exposed to the weather.