Using Cast Stone In Building and Construction – All You Need To Know
What is cast stone? How does it compare with natural stone and how can you be sure to choose the right supplier for your project? This guide will provide all the answers to your cast stone questions.
Cast stone is a unique material that provides multiple benefits for builders, developers and architects alike. A cost-effective alternative to natural stone, cast stone is chosen for its durability, versatility and strength, as well as its beautiful appearance. In this blog we explore the many benefits of choosing cast stone over natural stone and provide a complete guide to the material options available, manufacturing process and advice on specifying cast stone.
What is cast stone?
Cast stone is a special type of reconstituted stone. In building and construction cast stone is often preferred due to flexibility of installation and adaptability to create structural components. It is regularly used as an alternative to quarried stone as it looks, performs and weathers similarly to natural stone, but at a fraction of the cost.
Cast stone is also chosen over natural stone for its strength, colour, texture and for its freeze/thaw resistance. As it is free from the naturally occurring imperfections and stratification, found in quarried stone, it is much more versatile and adaptable than its natural alternative.
Cast stone is defined by the United Kingdom Cast Stone Association (UKCSA) as:
“Any product manufactured with aggregate and cementitious binder intended to resemble and be used in a similar way to natural stone”.
History of cast stone
The use of cast stone as a structural material dates back thousands of years to ancient Rome, where pozzolanic cement was used along with other natural aggregates. Many important buildings and structures were created using this new combination of building material, including the vaulted arches and gateways of Rome’s Colosseum and the large span dome of Athens’ Pantheon.
Cast stone has been used by numerous civilisations since its early beginnings and a full history of its use can be found on the UKCSA website.
How is cast stone used?
Cast stone has been used for centuries, but it had a renaissance in Georgian Britain, where many prestigious residential properties and public buildings were constructed using the material.
These days cast stone is chosen by builders, architects and developers around the world to complete architectural details of residential and commercial projects alike.
Cast stone is often the go-to material choice for standard and bespoke facade stonework including porticos, window heads and sills, string courses and quoins.
It is also widely used by manufacturers of garden and landscaping designs for balustrading, steps, copings and cornices, as well as garden buildings such as orangeries, temples and pavilions.
The benefits of using cast stone
There are many benefits to choosing cast stone instead of natural, quarried stone.
These are:
- Similar look and performance to natural stone, at a fraction of the cost
- Designs can be replicated at volume quickly and cheaply offering huge cost savings compared to carving natural stone
- Durable and sustainable
- High compressive strength
- Adaptable – can be structurally reinforced
- Versatile – broad design, colour and material matching options available
- Easy to integrate fixing and lifting sockets
- Weathers well.
Cast stone’s versatility
Because cast stone components are produced using moulds, almost any design specification can be met, making it a very versatile material. Standard and bespoke designs can be produced with highly intricate detail, integrated structural reinforcing and lifting sockets, in contemporary, classical and traditional styles.
Cast stone is also regularly chosen by developers who need to create large volumes of the exact same components. Cast stone designs can be replicated in large quantities quickly and relatively cheaply, making it a much cheaper option that carved, natural stone.
Cast stone can also be easily used for both internal and external new-build projects and retrofit requirements. Plus, because it can easily match natural stone based on aesthetics and performance, cast stone is often the natural choice for restoration and renovation projects.
What is cast stone made from?
The constituents used to produce cast stone include:
- Natural aggregates
- Cementitious binder (often white cement and sand)
- Water
- Pigments (for colour matching if required)
- Waterproofer
Colour and material matching to existing stonework is possible, making cast stone the ideal choice for restoration, renovation and retrofit projects.
Most manufacturers aim to create cast stone that resembles natural stone as closely as possible.
How do we select our natural aggregates?
How is cast stone made?
Creating the moulds
There are two types of moulds we use in the production process: wooden moulds, for simple designs like window sills and coping stones, and rubber moulds for complex designs. Here’s how the fibreglass rubber-lined mould is created:
- The model is created within our wood shop, having been carved from scratch by an in-house craftsman.
- Once the master model has been created, the mould-making can begin, starting by rolling clay to a set thickness and covering the entire model.
- A fibreglass case is then formed. It’s completely inflexible, so has to be designed to allow for easy removal later on – in some cases this means the fibreglass comprises ten sections or more.
- The fibreglass case is then opened, the model extricated and all traces of clay removed before being reassembled.
- A specially developed rubber is poured in, with enough fluidity to fill every cavity left where the clay was,while avoiding any air bubbles.
- Once the rubber is set, the fibreglass case is opened once again and the model is placed into storage. Once reassembled, the void left in the centre is the precise shape and size of the finished design.
The manufacturing process
For Haddonstone (semi-dry cast limestone), the materials involved in this are limestone, white cement, sand, a small amount of water along with some secret ingredients. This mix produces the Portland colour – for other colours, pigment is added. We have two other materials as well: TecStone (wet-cast limestone) and TecLite (fibre-reinforced). Here’s how it works:
- Quality check To ensure complete control of the production process, every single batch of raw material is checked for quality before use.
- Mixed in small quantities After being stored in high tonnage silos, the ingredients are mixed in small quantities via computer-controlled batching equipment, then taken to a workstation.
- Mould packing The mixture is then gradually packed into a mould, usually by hand, although sometimes pneumatic hand rammers are used.
- De-moulding Perhaps the most visually rewarding stage of the production process, the fibreglass case is stripped away, leaving the rubber around the stone. The rubber is then also carefully peeled away to reveal the stone design in all its glory.
Curing
Curing is an essential process applied to de-moulded cast stone as it helps both its appearance and long-term strength and durability.
The curing process can take over two weeks to complete, depending on the size of the cast stone component.
To speed up this process and ensure our clients receive the highest-quality cast stone components quickly, we have invested in an accelerated vapour curing chamber at our manufactory.
What options of cast stone are available?
We offer three high-specification cast stone material options to suit your unique requirements:
1. Haddonstone (semi-dry cast limestone)
This is a unique form of cast limestone, with a surface texture, feel and strength similar to Portland or natural limestone. The principal materials for this are limestone, white cement and sand, a mix which has a feel of damp sand or earth. This stone is packed into the mould either by hand or a pneumatic hand rammer. No finishing is required with this material due to the quality of the mould manufacture and casting, resulting in a look that’s virtually indistinguishable from natural quarried stone and weathers beautifully.
While displaying similar properties to that of natural stone, cast stone is significantly more cost effective piece for piece, making it the ideal choice for many ornamental and architectural products. Our vapour curing process gives the stone the equivalent of 14 days’ strength overnight, which results in reduced delivery lead times and improved handling.
Download Haddonstone Data Sheet
2. TecStone (wet-cast limestone)
We also manufacture products using a wet-cast production process – this material is called TecStone. Denser than our standard Haddonstone, it’s made of much larger particle sizes and exhibits a higher water content. The fluidity is created by plasticisers and super-plasticisers and the density of this material means that it doesn’t need vapour curing which means it doesn’t need vapour curing. Hand finishing is necessary at the end to ensure a high quality product. The TecStone mix is poured into a mould. This process gives a finish, once acid etched, much more akin to honed limestone. It has a smooth and sealed surface, which makes it ideal for flooring, fireplaces, complex statuary, larger architectural products and contemporary designs where clients prefer a surface finish that does not weather quickly. It’s also usually easier to clean for this reason.
We use TecStone for a number of our products, particularly those used in larger architectural projects, such as columns and paving. TecStone is designed to meet demanding performance criteria and as it can incorporate structural reinforcement, it tends to be the preferred material for architectural projects requiring structural strength as well as cast-in fixings.
3. TecLite (fibre-reinforced)
This revolutionary cement-based material contains alkali-resistant glass fibre (Glass Fibre Reinforced Concrete). Although it closely resembles cast stone in appearance, the use of thin wall construction teamed with GRC/GFRC technology means the component weight is reduced by approximately two thirds when compared with similar Haddonstone and TecStone pieces.
Its high strength to weight ratio makes it ideal for new build, retro-fit, timber frame and new build projects. It can also be used to achieve the same crisp detailing normally only achieved with Haddonstone designs. Robust and lightweight, TecLite can be used in conjunction with Haddonstone architectural components.
What specification is cast stone manufactured and supplied to?
The United Kingdom Cast Stone Association (UKCSA) states that all Full Members of UKCSA produce their cast stone to a higher compressive strength than BS 121.
As a founding member of UKCSA, all of our materials exceed the requirements of BS 1217:2008, BS5642-2: 1983 + A1 2014 and BS EN 13198: 2003.
We also regularly conduct quality checks on our cast stone materials, to ensure only the highest quality product reaches our clients.
Specifying cast stone – how to choose a cast stone supplier
According to the United Kingdom Cast Stone Association, choosing an UKCSA Member company gives the confidence required through the strict controls and standards adhered to, which include the manufacturing standards and procedures and third party testing and verification together with the social responsibility expected from a credible organisation.
They state:
All categories of cast stone products, whether semi-dry, wet-cast or fibre reinforced, have their relative advantages and should be considered as suitable or preferred alternatives to the natural stone they replicate. In addition to their manufacturing process is the quality of the raw materials, product durability, buildability, and most importantly the reliability, dependability and accountability of the manufacturer. Therefore it is essential that, whichever product category is selected, the supplier should be chosen extremely carefully.
How should cast stone be installed?
We strongly recommend that cast stone components should only be installed by an experienced and trained installer.
Our team will be able to assist you in finding a suitable installer in your local area.
How to point cast stone
We have a range of helpful assembly advice on our website, including recommendations for pointing Haddonstone (semi-dry cast limestone) and TecStone (wet-cast limestone).
How to maintain cast stone
For architectural projects, installers can often assist with the cleaning and maintenance of cast stone components. Our team can help you choose an installer in your local area.
To care for your Home and Garden stonework and to keep it looking pristine, you should remove any build-up of dust, dirt and grime. To do this, we recommend using a gentle, non-invasive method such as cleaning your cast stone with fresh, clean water before applying a mild, environmentally-friendly detergent with a soft nylon brush. Learn more about caring for your cast stone designs in our helpful blog.
Repairs to small areas, chips etc. can be achieved with our pointing mix.
Speak to our team
Whether you’re working on a private residential or large commercial project, or if you are interested in home and garden products, our friendly and expert team are happy to discuss your requirements.