In the 1920s and early 30s three pre-radar early warning sound mirrors and a 61m parabolic sound wall were constructed along the Kent coast to pick up the distant sounds of enemy bombers approaching across the English Channel. The acoustic detectors were some of the most advanced concrete structures of their time and are now listed by English Heritage as Scheduled Ancient Monuments.

Scope of Works:

• Reinstate deteriorated areas of concrete using site batched concrete repair materials to match the original concrete
• Install new reinforcement to stabilise the structures

They structures are in a very exposed marine environment but they have survived remarkably well which is testament to the quality of the original construction. However there was some concrete deterioration which put the structures at risk of collapse so English Heritage instructed CRL to undertake repairs.

The Ancient Monument listing meant that the repairs were never intended to fully restore the mirrors but to stabilise the structures for the future.

CRL developed a site batched concrete to match the original concrete for density, colour and texture. With the agreement of English Heritage the repairs areas were identified and repaired using hand placed mortars and cast flowable concrete. In some instances new steel was added by grouting bars into hand cut chases to minimize damage to the original concrete.

Client: English Heritage

Value: £62,000