2007 Yearbook

INSTITUTE OF HISTORIC BUILDING CONSERVATION YEARBOOK 2007 26 I N R E V I E W REDSAND FORT The last in a long history of British marine defences, Redsand Fort is one of three army forts built between May and December 1943 under the direction of civil engineer Guy Maunsell. Their purpose was to provide offshore defences to protect the area from air and sea attack, including the laying of mines by German forces. Approximately eight miles off the Whistable coast in Kent, Redsand Fort originally accommodated up to 265 men at any one time in seven towers. These are arranged in a cruciform – Searchlight Tower, G2 Tower, Control Tower and G1 Tower are aligned linearly north to south, with Towers G3, G4 and Bofors bisecting this line east to west at the Control Tower location. Each structure is made up of four hollow reinforced concrete legs which measure three feet in diameter and support a concrete slab and a 36 foot square two-storey steel house. At one time, these had military equipment installed on the top deck. Troops stationed at the Thames forts shot down 22 enemy planes and 30 German flying bombs, and were instrumental in sinking one U-boat. After the war, the forts were abandoned and the guns were removed in 1956. During the 1960s, the forts were best known for their use as the bases for several pirate radio stations; Redsand Fort was home to Radio 390. In the 60 years since their construction, the structures have remained largely unchanged and none has received significant maintenance or repair. Shipping collisions, organised dismantling and collapse caused by damage from salt water and severe weather have since led to the loss of some of these historic Thames forts. Further exposure to these extreme conditions places the remaining buildings in grave jeopardy if left in a continued state of neglect. SAVING THE FORT In 2004, the chairman of Project Redsand and former Radio Caroline sound engineer Robin Adcroft approached me to see whether Taylor Woodrow’s Technology Centre would carry out an investigation to appraise the fort’s overall condition, as well as to comment on what would be required in terms of repair, as considered necessary to stabilise the towers’ condition. I arranged for one of our specialist materials consultants to carry out a preliminary inspection by boat in July 2004, which focused mainly on Control Tower. We found the concrete above the low water level to be in generally good condition for its age and exposure. However, some defects were observed, including vertical cracks and some incipient spalls (areas of delaminated concrete cover that would soon detach from the main body of concrete). Most damage was visible at the tops of the legs and around the capping slabs which support the steel superstructure. A closer inspection was recommended, and this took place in June 2006, led by Richard Norwood- Grundy. This examination was carried out principally from G1 Tower, which now benefits from a permanent berth and ladder access up into the enclosed steel structure above. In addition to viewing this fort at close quarters, the remaining forts were viewed using binoculars from the top of the steel structure, while a water level view was also provided by boat. Our investigation found clear evidence of reinforcement corrosion to G1 Tower, which manifests as linear cracking with occasional rust staining observed at the top of the raked legs. The exposed reinforcement on the underside of the capping slab showed further evidence of corrosion and spalling, which would be expected given the age of structure and its aggressive marine environment. In this case, the cracking may have been affected by torsion, as it is understood that the original design of the towers accommodated the recoil from the anti-aircraft ordnance secured at the top of the steel structure. This design allowed the raked legs to twist slightly to absorb some of the impact that occurred when the guns were fired. It is possible that these cracks have propagated in response to these forces. However, with the passing of time, salt-laden seawater has penetrated to the reinforcement via these cracks and hence corrosion has developed, causing the cracks to widen still further in response. Our inspections of G1 and Control Tower provided a good indication of the condition of the Redsand Fort as a whole. It is considered that the existing defects are gradually worsening with time and remedial work is strongly recommended to preserve the historic structure. Given the age and exposed location of these buildings, their condition is considered reasonable and as such fully salvageable providing that repairs are instigated in the short term. With modern technologies now at our disposal to assist with the conservation of Britain’s historic buildings, a number of options are now available in order to safeguard Redsand Fort for the long-term, ranging from patch repairs to electrochemical protection. More in-depth inspections, sampling and testing are recommended to be carried out in the near future. Tests, such as cover measurement, chloride content, carbonation depth, half-cell potential and concrete resistivity will be required to determine the scale and nature of material deterioration. In addition, these tests will help us to evaluate what type of repair will be most successful in the long-term and will guide us in the provision of a bespoke solution to this unique and fascinating building conservation challenge. I and the rest of the Taylor Woodrow team look forward to offering our continued support to Project Redsand and to seeing this significant piece of our heritage preserved for generations to come. Further information TaylorWoodrow Technology Centre: www.taylorwoodrow.com/ technologycentre Project Redsand: www.project-redsand.com The view from G1 Tower, Redsand Fort (Photos: Project Redsand)