When the people of Guernsey decided to build a lighthouse 1 mile off the coast following a shipwreck in 1910, few imagined the difficulties involved in repairing the concrete foundations 87 years later.
The Platte Fougere lighthouse may have survived two World Wars, but years of being constantly bombarded by waves had eroded its walls, leaving it in urgent need of repair. Determined to find a longterm repair solution, the State of Guernsey Board of Administration called in Ronacrete. Previous attempts to resurface the lighthouse failed because the continuous pounding of the sea had attacked the repair material.
Ronacrete had provided valuable technical support on other tidal projects in the region and was aware of how tricky applying repairs 1 mile out at sea would be. It carried out a full analysis of the problem and stressed the importance of using a waterproof and weather resistant material and the need to work in the summer when more favourable tidal and weather conditions could be expected.
It was essential that the repair mortar gained strength quickly because of the threat from the tides, while the dangers involved in working on the exterior of a lighthouse meant six men had to be present while the repairs were being carried out; three in a boat in case someone fell into the sea, two to mix the mortar on the scaffolding, and one to apply the repair material.
Ronacretes rapid set mortar Monoset RX (now available as RonaBond HB40 Ultra Rapid) was chosen because it sets in 1 hour and is designed for hand mixing in small volumes and works best when mixed close to the area of application. As well as achieving rapid strength, Monoset RX is waterproof and continues to function at low temperatures, including below freezing.
As a precaution, Ronacrete recommended that the contractor inserted steel dowels which protruded from the wall so the mortar could bond to them if the ageing substrate was too weak.