The How It's Made
TV crew filming stone being packed into a mould at Haddonstone's Northamptonshire manufactory.
Each Haddonstone design is made to order. If the order is for a standard design, production can commence as soon as a colour has been agreed. If a custom design is required then a mould needs to be made. If the design is relatively simple, a window cill or coping stone for example, then the mould will be made of wood in the company’s wood shop. One of the skilled carpenters will interpret drawings to produce a precise mould, which is the exact reverse of the shape ultimately required. Timber moulds have a comparatively limited life compared to their fibreglass equivalents. However, the speed with which timber moulds can be produced, combined with their relatively low cost, normally makes this type of mould more economical for the client.
The production of a fibreglass, rubber-lined mould in the company’s studio is much more time-consuming and is only undertaken if the design is complex or if there are likely to be numerous castings over time. The work is one of the most highly skilled within Haddonstone, benefiting greatly from artistic and practical skills. Before such a mould can be made, it is first necessary to have a model. This can come from a variety of sources: it could be created by the neighbouring wood shop; it could have been carved from scratch by an in-house craftsman, normally in plaster, either replicating an antique piece for a restoration project or afresh for a new design; it could be a pristine antique stone; or it could be a damaged original requiring restoration.
Once the master model has been created, the mould-making can begin. This is done by rolling clay to a set thickness and covering the entire model. Over this a fibreglass case is formed. As this case will be completely inflexible, it has to be designed in such a way as to allow its later removal. For this reason, some fibreglass cases can comprise more than ten sections. Then the fibreglass case is removed, the model extricated and all traces of clay removed. The case is then reassembled around the model, there now being a void where the clay had previously been. Into that void is poured a specially developed rubber which has enough fluidity to fill every cavity whilst avoiding any air bubbles which would be seen in the finished design. After the rubber has set, the fibreglass case is, once again, removed and the model extricated for storage. When the fibreglass and rubber case is reassembled, the void now left in the centre is the precise shape and size of the finished design. Particular care is taken to ensure that any seam is in a position where it is least noticeable. Whether wooden or fibreglass, without a first-class mould it is impossible to create a first-class product.
For semi-dry cast Haddonstone, the principal materials are limestone, white cement, sand and a small quantity of water. This produces a Portland colour with other colours requiring the addition of pigment into the mix. Other key ingredients include plasticisers to improve workability and aid compaction as well as waterproofers for durability. To ensure complete control of the production process, every single batch of raw material delivered to the Haddonstone manufactory is quality checked, before it is used. The constituents of the mix are stored in high-tonnage silos adjacent to the production area, before being mixed in small quantities via computer controlled batching equipment and taken to a workstation. At this stage, the mix has the feel of damp sand or earth.
The stone is gradually packed into the mould using a number of ingeniously crafted tools. Whilst this is normally done by hand, some moulds can be packed using pneumatic hand rammers. Once packed, the stone is left in the mould until the next working day. The process of delaminating or stripping is probably the most visually rewarding of the entire production process, particularly for a fibreglass mould. The fibreglass case is first stripped away, leaving the rubber around the stone. The rubber is then carefully peeled away to reveal the stone design in all its glory. No finishing is required as the quality of mould manufacture ensures that the design is perfect. It is at this stage that the first of many quality control checks is undertaken and the product is given a bar code label, which will remain with it until delivery to the customer. The stone is now strong enough to be transported outside the production area.
Like other companies in the industry, Haddonstone originally relied on the vagaries of the English climate to ensure that the stone cured correctly. However, the effects of temperature, precipitation and wind made this a very inexact science. For this reason, the company introduced a vapour curing system in 1999 that gives the stone the equivalent of fourteen days strength overnight. Not only does this give the company a guaranteed curing system, it also reduces delivery lead times and storage problems.
Although some customers opt to collect their orders, most rely on Haddonstone’s own transport fleet, the majority of which include a demountable forklift to aid off-loading on site. Export orders are dispatched by container or in specially constructed wooden crates. A similar operation to Haddonstone’s manufactory in Northamptonshire exists at the company’s US manufactory in Colorado. In the UK and USA, Haddonstone also manufactures products by a wet-cast process, called TecStone. Here, the mix is poured into the mould. This process gives a finish, once acid etched, much more akin to Coade stone and is ideal for larger products, complex statuary and contemporary designs where clients prefer a surface finish which does not weather quickly. Most recently, Haddonstone has developed an artificial stone reinforced with glass fibres, called TecLite. Products made by this process have thinner walls and are consequently lighter.