August 2021
Many older buildings on the Island are built with “Island Stone”. In the north of the Island this is Bembridge Limestone. Much of this stone was exported to the mainland.
The harder type, called Quarr Stone, quarried around Quarr and Binstead, was used in the building of Portchester Castle by the Romans. Later it was used in Chichester and Winchester cathedrals. Export of stone by water was easier than by road.
Upper Greensand stone is also to be seen in Island buildings, generally to the south of the Island. Several quarries were dug at Bonchurch and Ventnor. Before the 16th century, stone was mainly used in special buildings, such as churches and Carisbrooke castle. Bonchurch Old church is an example of this, and the newer Victorian church at Bonchurch was constructed on the site of one of the stone quarries.
A new stone wall at Millfield, Ryde
During the 17th century, more manor houses, farm houses and larger cottages were also being built of stone, as landowners preferred the durability of stone. It was also widely available, with small quarries being used nearby.
Often the stone was not laid in courses, but just randomly as the shape of the stone permitted. Two rows of stone would be constructed to make a single wall, and the centre filled with rubble. A lime mortar would be used to stick the outer stones together.
Repairs to Bonchurch Old Church
Limestone or chalk would be burnt in a kiln and then the resulting powder was added to sand to make the mortar. Limekilns were often located within easy reach of water transport at the head of a creek, or near to the source of the limestone to reduce transport distances. A typical kiln was circular, three to four metres in height, and built of sandstone. Brushwood at the base below a grid was fired, igniting layers of poor coal and limestone that had been loaded from above.
Today, repair of stone walls is an art. Lime mortar allows the stone to breathe, whereas cement mortar holds damp in and cause the stonework to crumble. In Listed Buildings the mortar must be analysed to find a matching mixture, and sometimes it is found to have particular grit or chalk nodules added.