Precast façade cladding
Wet and dry cast precast units are an alternative to natural stonework. Find out more about these options as available through PMJ Masonry.
Selecting wet or dry cast precast elements for a project is an option where it is the general preference or where the solution lends itself as a better outcome, be it aesthetically or structurally when considered against larger project design and material preferences. Examples include band courses and lintols within a general brick and glazed façade, as roof level copings or as an aesthetic solution when marrying with an existing or adjacent building.
The use of cast stone can be traced back as far as the 12th century, where an early application of the technique survives in France. The wider use of cast stone became prevalent in London in the 19th century. With labour and material shortages being an issue during reconstruction post World War 2, the adoption or cast stone and concrete in general became much more mainstream, coincidental with the first publication of BS1217, Specification for Cast Stone, first published in 1945.
The cast stone industry is supported by the UKCSA – United Kingdom Cast Stone Association. For technical guidance, reference should be made to the UKCSA Technical Manual, along with BS1217 for the design of smaller un-reinforced and lightly reinforced units and BS8297 for larger reinforced panelised precast.
Precast cast elements are formed either through a dry or wet cast manufacturing technique. Both use moulds to create the shape of the required unit. The adoption of one form of manufacture over the other is largely driven by the design purpose of the unit: from its size, weight and the need or otherwise for reinforcement, mechanical lifting provision and lastly, surface finish.
At the simplest of levels, small walling units are typically dry cast – these are normally unreinforced and can be manually handled or when required, lifted by mechanical means independent of the unit design. Larger and longer units (where due to structural or lifting considerations, reinforcement is required) lead to being wet cast and are normally finished with an acid etching wash.
Dry cast stone is a semi-dry, colour tinted, concrete mix which is tamped into moulds in layers, achieving a compact result with no voided entrapped air within the concrete or on the face of the mould.
Due to its low water content, it has a quick curing time and therefore the units can be demoulded after a short period, allowing them to be reused several times per day. This leads to dry cast manufacture being an efficient option for regular unit mass production.
An alternative to dry cast, wet cast (as the name implies) is a wet concrete mix (appropriately colour tinted) normally used in conjunction with reinforcement, to form larger, more complicated, and generally more bespoke precast units.
Wet cast manufacture is ideal for use when there is a load-bearing requirement, structural spanning is required, or where there is a high degree of environmental exposure.
Wet cast concrete mixes are normally free flowing and self-compacting to allow for solid contact for rebar encasement. Through having a higher water content, the cast unit must be left overnight prior to being demoulded. Once cured for a week or so, the units are normally acid etched resulting in a consistent slight etched finish, complementary to that of stone.
Through adopting mould inserts or using a chemical application that delays local surface curing, patterned, textured, and exposed aggregate finishes can be achieved.
At PMJ Masonry we possess the in-house expertise to manage the design, supply, and installation of stone-faced precast panels.
We have collaborated with precast suppliers who have the trade and technical skills through joinery and rubber mould technology. This enables us to replicate the most complex, detailed bespoke masonry, from wet cast techniques up to and including the most intricate of classical columns and heads, including the most ornate of the classic series of column design – Corinthian capitals.
Please contact PMJ Masonry to discuss your precast cladding project needs.