An appreciation of the past and the need to conserve historic buildings and architecture has led to an .increased use of case stone as a substitute to quarried stone. Looking at the two types of materials available, it is clear that cast stone is the preferred choice for architects.
There have been more imitations of stone than any other natural building material and the incredibly versatile cast stone is a prime example. The ability to mould cast stone to almost any shape means you can create new designs or faithfully reproduce replicas that are virtually indistinguishable from an original. The cast stone material matures and weathers like natural stone yet costs significantly less than quarried stone – making it an ideal solution for a restoration project.
A fine example of the use of cast stone for restoration is demonstrated on the restored Scarborough Spa, a Grade II listed building built in the 19th century. The architectural stonework detail of the building was subject to exposure of salt water from the North Sea. Therefore a robust material was required in order to restore the building to its former glory. Following strenuous salt crystallisation and water absorption tests conducted by the BRE laboratories, it was decided to commission a cast stone manufacturer for the restoration.
Production techniques: getting the mix right
The finest forms of cast limestone are manufactured using a semi-dry mix that creates a surface texture similar to Portland stone or natural limestone. The principal materials of semi-dry cast stone are limestone, white cement, sand and a very small amount of water, giving the mix a damp feel.
A reputable manufacturer will ensure that every single batch of raw material is quality checked to ensure complete control of the production process and enable a high quality end product. The semi-dry cast material is gradually packed into moulds using pneumatic hand tools. The material is usually left overnight to cure before the stone can be revealed in all its glory.
Again, reputable manufacturers will employ a curing system to prevent water loss and ensure that the product achieves optimum strength in excess of relevant British standards. This would ensure that architects, developers and private clients can have every confidence in the durability of the product for their restoration project.
There are alternatives to the dry cast mix in the form of wet-cast and fibre reinforced stonework production. The unique wet cast production technique produces a denser cast stone material with a smoother finish to meet demanding design and performance criteria specified in refurbishment or restoration projects. The innovative fibre-reinforced cast stone production benefits from drawn glass fibre which has a high strength to weight ratio. Its thin wall construction and GRC technology means the component weight is reduced by approximately two thirds when compared with alternative cast stone production methods. Fibre-reinforced cast stone is ideal for retro-fit, refurbishments, timber frame and new build projects where weight is an issue.
The choice of cast stone material depends on the constraints of the restoration project along with the client’s individual requirements. Whether you are refurbishing an existing property or restoring an historic building, cast stone provides an economical solution for replica stonework and custom designs.
Simon Scott is a director of Haddonstone Ltd