The Cast Stone Self-Builder’s Guide

Cast stone is a remarkably versatile construction material that is suitable for all types of self-build project including new-builds, extensions, renovations, refurbishments and conversions.  While it is often used to replicate natural stone features on period properties, cast stone is equally appropriate for add striking details to contemporary designs.  Furthermore, cast stone complements brick-faced, rendered block-built and rendered timber-framed properties.  Benefiting from reliable deliveries and being easy to design with and install, cast stone offers maximum impact for minimum effort and cost.

Extensive ranges of standard products are available either for delivery from stock or on short lead times, or bespoke products can be manufactured to order in colours and finishes that, to the untrained eye, are indistinguishable from natural stone.  Cast stone also offers an exceptional degree of design freedom; almost any three-dimensional geometric form can be cast, incorporating elegant curves as well as straight-edged features and intricate details.

Applications

As a cost-effective alternative to natural stone, cast stone has historically been used for repairs, alterations, extensions and conversions of older properties.  Likewise, it is popular for new developments that are designed to blend in with their older surroundings, or where planning authorities insist on traditional features for developments in sensitive areas.Another very popular use for cast stone today is in properties where the desire is to add individuality, style and impact.  Features that would traditionally use natural stone can be executed very cost-effectively in cast stone, such as porticos, balustrades and arches.

Procter Cast Stone has a portfolio with dozens of standard products that can be manufactured in standard or bespoke colours.  Alternatively, cast stone units can be manufactured to customer-supplied drawings – and even a one-off cast stone product can be cost-effective compared with natural stone.  Nevertheless, one of the advantages of cast stone is that the manufacturing process uses reusable moulds.   And when products are manufactured in higher volumes, the economies of scale make cast stone extremely attractive.  For that reason, cast stone is an excellent way to add real value – as well as character and style – to properties.  Indeed, research has shown that cast stone makes houses more attractive to prospective purchasers to the extent that they would be prepared to pay more – much more than the marginal additional cost of using cast stone.

What is cast stone?

Cast stone, which is sometimes referred to as reconstituted stone, simulated stone, artificial stone or Artstone, starts with a drawing, from which subsidiary drawings are prepared so that a skilled pattern maker can create a wooden mould.  Depending on the product and finish required, cast stone is made using a semi-dry mix of white and/or grey cements with natural or manufactured sands.  The appearance of natural stone is achieved using crushed natural stone, well graded natural gravels and mineral pigments.  A waterproofer is also added to minimise moisture absorption and improve resistance to frost damage. On larger components, a coloured facing mix is used on the outside of the mould, with a higher-strength, non-coloured backing mix in the interior.  Cores are sometimes used to reduce the volume of cast stone used and, therefore, the weight of the final product; reinforcement can be also be incorporated to enhance the structural strength.  Additionally, bosses for lifting eyes can be set within the casting to ease handling on site.

During mould-filling, the semi-dry mix is compacted using a vibratory ram.  The casting is turned out almost immediately, enabling the mould to be reused straight away if required, and the cast unit is allowed to cure initially in a controlled environment and then naturally.  In extreme circumstances, cast stone products can be manufactured and delivered to site within approximately two weeks, provided the correct mould is available. After installation, cast stone weathers in the same way as natural stone.  If required, it can also be cleaned or repaired, and conventional masonry fixings can be used to attach other items.

Products intended for use in compression – such as quoins, string courses and walling units – can be structural.  However, cast stone lintels and other units that might experience tensile loads should be used in conjunction with a suitable structural lintel.

Design Freedom

Almost any three-dimentional geometric form can be cast, including curves and straight-edged features.  Additional detail can also be incorporated into the surface, such as brick-effects, channels or decorative designs, and the edges of units can be square, beveled or radiused.  Cast stone greater design freedom than natural stone as, for example, slender units can be manufactured with integral reinforcement, which would not be possible with natural stone.  However, the ‘slenderness’ ratio of the unit’s length to its ‘diameter’ (an inscribed or superscribed circle on the section of the product, determined by the support plane) should be less than or equal to 12 unless otherwise agreed with the manufacturer.

Cast stone units can complement brickwork, natural stone, flint or rendering.  Standard colours are available to match those of natural stone, such as Bathstone, Red Sandstone or Portland stone, while non-standard colours can also be produced to meet a client’s specific requirements.  Colour samples can be supplied so the architect – and client – can see the actual colour and finish.

Note that the colour is exceptionally consistent, both between units manufactured within the same batch and from one batch to the next (though controlled variation can be introduced to mimic the effect seen when natural stone is used for walling, for example).  This complete control over the colour is in contrast to the lack of consistency available from quarried stone.

Various surface finishes and textures can be achieved using the cast stone process, so it is essential that the requirements are discussed with the manufacturer.  This is especially so if exceptionally smooth surfaces are being considered, as the type of finish has a significant effect on the overall appearance of the product.

Any exterior feature that might be cut or carved from natural stone can also be executed in cast stone, such as:

In addition, interior features such as fireplaces and door surrounds can be produced to architects’ designs.

Working with Cast Stone

As stated above, a cast stone unit starts with a drawing.  Today this is usually in the form of a CAD file for bespoke products, though drawings prepared by hand are equally acceptable.  If required, CAD files for standard products can be supplied to architects who wish to incorporate these within their designs.

If a design calls for numerous similar but slightly different units, Procter Cast Stone can ensure that these are delivered to site with suitable identifying marks.  Corresponding unit location plans eliminate any ambiguity over where they need to be installed.

Whether standard or bespoke units are being considered, it is advisable to contact the manufacturer as early as possible.  Doing so enables the cast stone units to be designed so as to minimise the manufacturing cost.  There are also design tips that can be passed on, such as ensuring that there is on major flat unexposed surface for the open side of the mould (while this is not essential, not having a major flat unexposed surface increases the mould complexity and unit cost).  Similarly, certain design details can be easier or more difficult to produce – and the difference is reflected in the price of the units.

When the unit drawings are being prepared, it is important to identify which surfaces will and will not be visible once construction is complete.  This enables the manufacturer to incorporate threaded sockets for lifting hooks in positions that will not be seen.

As well as advising on design details for cast stone units, the manufacturer can also provide information relating to fixings, mortars, on-site handling, aftercare, cleaning and repairs.

Procter Cast Stone can arrange deliveries to site according to an agreed schedule.  This avoid delays to site work due to late deliveries, plus the cast stone units do not spend any more time on site than is necessary, which helps site logistics and minimises the risk damage.  On the other hand, if the project is delayed for any reason, deliveries can be rescheduled accordingly.  Guidelines for handling are available to minimise the risk of damage.  However, should an accident occur, minor damage can often b repaired on site, or replacement units can be manufactured and delivered to site within around two weeks.

No specialist skills are required for installing cast stone units beyond those needed for bricklaying, and no specialist equipment is necessary (unless lifting gear is required for heavy units).  More information about site handling, installation and cleaning is available on request.

Procter Cast Stone seeks to develop close relationships with clients by providing high-quality products backed up by comprehensive technical support and reliable, personal service.  A dedicated planner is assigned to every project, large or small, to ensure that all aspects of the work meet with the client’s requirements.

As with any other building material, it is vital to take care in selecting a supplier.  There are many manufacturers of cast stone that do not adhere to quality assurance standards or even to the main standards relating to cast stone.  Architects should satisfy themselves that their selected supplier will deliver a high-quality product and a high standard of service.

Where To See Cast Stone

We are happy to show prospective customers or specifiers completed projects in their area or make arrangements to view the manufacturing process at Procter Cast Stone’s factory in Garforth, Leeds, where design options and project details can be discussed.

Procter Cast Stone website has brochure, specifier’s guide to cast stone, PDFs of product drawings and illustrations of the standard colours available.  In addition, there are case studies, photographic gallery that shows a wide variety of cast stone applications, plus there is a facility to register for a free email newsletter.  Whatever plans self-builders have in mind for cast stone, Procter Cast Stone can provide the technical and design support to help them realise their ideas.