Castle Drogo Restoration
Granite blocks needed to be removed from a National Trust castle without damage or any marks.
Castle Drogo on the edge of Dartmoor in Devon, was the last castle to be built in England. However, of all the hundreds of castles ever built in Britain, this is one that has never had to endure an attack or a siege as it was only completed in 1930.
Castle Drogo, despite its youth, now faces a far more deadly enemy, “the weather”. Its vast roof is leaking, as well as its 900 windows and the pointing between the enormous slabs of granite are letting in water. The National Trust, has launched a campaign to raise the estimated £11 million needed to make the castle watertight. The work is expected to take around 5 years to complete.
In various areas some of the granite ashlars blocks had to be removed so that repairs could be made to make it water tight. The building is protected by a conservation order so none of the visual elements of the stonework can be altered or damaged. Failure to comply with this is classed as an offence!
The contractor commented:- 'When asked to cut out large individual granite ashlars on Castle Drogo at the start of a £6M contract; we decided to carry out some trials. As the Castle is a Grade 1 listed building, we needed to take special care not to touch or mark the stone. The first job was to remove the pointing to a depth of 20mm with hand tools. This exposed the arises and the size of the joints.
The mortar joints were approximately 10 to 12mm wide and between 250 and 400mm deep. A cut was made through the centre of the joint with a 9" angle grinder, taking care not to come into contact with the stone. Next a hammer drills drill was used with masonry bits to stitch drill out the mortar. This process took between 12 & 19 hrs to free the ashlars. It also used approximately 24 drill bits per stone and took a large toll out of both the drill, and the mason.
The next method tried was a diamond chain saw with blades to suit the depth of cut required. EC Hopkins Ltd, the UK master distributors of ICS based in Birmingham, attended site to carry out the trial cut using the ICS 880 Hydraulic Chainsaw, powered by an EC Hopkins 3 phase power pack. The first ashlar was removed in under 30 minutes. The cut was clean, easy to control and fast making it a major improvement over any other method.
As you can see from the photos a cut was made in the mortar joint all around a block (taking care to avoid contact with the block face and the surrounding blocks) it was then finally eased out with a crow bar. The actual cutting time was 25 minutes, compared to the time and method described in the above quote. the contractor, adopted this improved method and the advice and training that EC Hopkins provided, and continued its journey on helping make Castle Drogo water tight again.
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