That is the question posed to Toby Marlow, Building and Construction Director
at Haddonstone
Natural stone has been used in and for construction for thousands of years and seen in some of the world’s most prominent and historic buildings, monuments and works of art. With a long and illustrious history, cast stone became a preferred building material in the eighteenth century when classically inspired country houses were increasingly popular.
Often regarded as a superlative material, the unrefined, organic composition, stability and appearance of natural stone makes it an established choice in the architectural industry. Yet sourcing and working with natural stone has its drawbacks, and architectural cast stone offers specifiers an easier to use, more cost-effective alternative.
Here, we explore the main differences between cast stone and natural stone and why cast stone is often the preferred choice for a broad range of building projects.
What is the difference between natural and cast stone? - Natural stone has been excavated from the ground via quarrying; stone is raked from the exposed surface of natural rocks. As an organic material that has undergone many years of geological change, all types of natural stone are unique, offering subtle or significant variations in grain, texture and colour. Today, the most common natural stones that are extracted are limestone, marble, granite, slate, sandstone and travertine. Once excavated, these stones are cleaned, cut into varying shapes and sizes as required, and finished.
Cast stone by contrast is a special type of reconstructed stone, produced using a blend of limestone, pigments, additives, sand and cement. The mixture is then poured into specially created moulds before being cured and/or finished.
Cast stone is defined by the United Kingdom Cast Stone Association as “Any product manufactured with aggregate and cementitious binder intended to resemble and be used in a similar way to natural stone”.
What are the drawbacks of specifying natural stone?
Whilst natural stone offers many benefits, there are drawbacks to using it as a construction material. The main issues with specifying natural stone for building projects are:
Consistency – naturally occurring imperfections and stratification are very common in natural stone
Availability – meeting exact project specifications with a natural material like stone can be difficult
Cost – natural stone is very often prohibitively expensive
Time – the process of extraction, cutting and finishing is time consuming and can increase project lead times
Carbon footprint – many natural stones are imported into the UK from Asia and southern Europe, which adds significantly to their carbon footprint.
What are the benefits of specifying cast stone?
Natural stone has been imitated more than any other building material to date. Cast stone offers an impressive alternative. Here are some of the main benefits of specifying cast stone:
Appearance - high-quality cast stone has the appearance of natural stone and is almost impossible to distinguish from its quarried equivalent.
Versatility - because cast stone components are produced using moulds, almost any style and scale can be achieved. This includes highly intricate designs and patterns, which would be prohibitively expensive using natural stone. Plus, colour matching is also possible with cast stone, making it the ideal material for restoration and replication, as well as new-build projects.
Cost - like for like, in most cases, as a reconstituted material, cast stone is a far more competitively priced material than natural stone. The cost, therefore, not only decreases project risk, but opens up a wider expanse of architectural possibilities.
Performance - with a minimum cube compressive strength of 35 MPa, cast stone can significantly withstand load and, if specifying wet-cast stone, reinforcement can be added to produce structural loadbearing units.
Durability - cast stone weathers similarly to natural stone and has sound freeze/thaw resistance, so is easily able to withstand even the harshest of weather conditions. Also, there is no natural strata in cast stone which can be a weakness in natural stone.
A joint research programme between the University of Dundee and the United Kingdom Cast Stone Association (UKCSA) on the performance and durability of cast stone found that “all cast stone products, and particularly when waterproofed, were found to be highly resistant to carbonation. Efflorescence did not occur in any of the test samples and weathering in cast stone was similar to that in control natural stone. The data also suggests that dry cast, cast stone is no less vulnerable to frost attack than natural stone”.
Find out more about the frost resistance of cast stone in a guest blog by Neil Sparrow, Director of the United Kingdom Cast Stone Association and an industry expert in the manufacture of cast stone products. For further information, call 01604 770711 or visit www.haddonstone.com
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