Unravelling the options for cast stone specifications

There are three cast stone options available for architectural projects. Simon Scott of Haddonstone explains

Cast stone is one of the most versatile building mat-erials available and, in a number of important ways, is markedly superior to quarried stone. One of its greatest advantages is price, which, piece for piece, is normally significantly less than that of the quarried alternative. There are three high-specification cast stone options for specifiers.

Semi-dry cast limestone

The finest semi-dry mix designs replicate the texture and feel of Portland and Bath stone, while exceeding their strength. Such cast stonework weathers beautifully to become virtually indistinguishable from its quarried stone equivalent, making it ideal for decorative ornamental and architectural designs. The principal materials for semi-dry cast stone are limestone, white cement, sand and a very small quantity of water. The mix has the feel of damp sand or earth before compaction. The stone is packed into the mould using a number of ingeniously crafted tools. This is done by hand or by using pneumatic hand rammers. No finishing is required due to the quality of mould manufacture and casting technique.

Wet-cast limestone

Some specialist companies also manufacture products by a wet-cast process. Here, the mix is poured into the mould. This process can give a finish, once acid etched, much more akin to the famous Coade stone and is ideal for larger architectural products, flooring, fireplaces, complex statues and contemporary designs where clients prefer a surface finish which does not weather quickly. The stone produced by the wet-cast process is considered to be a high specification stone designed to meet demanding design and performance criteria for commercial projects and large or small scale individual private developments. Hand finishing is required to ensure a quality product.

Fibre-reinforced stonework

Fibre-reinforced stonework benefits from glass-fibre reinforced concrete (GRC) technology, which closely resembles traditional cast stone and natural stone in appearance – yet the use of thin wall construction GRC materials means the component weight is reduced by approximately two thirds when compared with similar dry-cast and wet-cast pieces.

Fibre-reinforced stone is a high specification cement based material containing alkali-resistant glass fibre, which benefits from a high strength to weight ratio. Architectural products made by this process are ideal for retrofit, timber-frame and new build projects.

High specification fibre-reinforced products can be used in conjunction with other semi-dry and wet-cast architectural components as the colours should be complementary. Consequently, users can incorporate different materials in the same project with absolute confidence. Fibre-reinforced products achieve the same crisp detailing normally only associated with semi-dry cast and wet cast designs.

Reputable cast stone manufacturers ensure the materials comply with stringent UK and European standards as well as exceeding the compressive cube strength requirements of BS1217:2008. Some manufacturers also put their cast stone through rigorous tests in order to further ensure the reliability and durability of the material for use, including vigorous salt crystallisation and water absorption tests (conducted by the renowned BRE laboratories) as well as the strenuous Canadian freeze-thaw tests.

One of the great advantages of using all three cast stone materials from a single reputable company is that they can be successfully used alongside each other on the same project. All three types of cast stone provide quality, longevity and value for money. The choice of which material to use can be based on a client’s individual preferences, specifications and requirements. Whether using a single type of cast stone or all three combined, most projects can be completed solely using material from a single reputable company.