STUCCOAn English Tradition
A mix of sand (or another base such as powdered marble or ground glass), lime and [Portland] cement applied while wet to create a durable exterior rendering for masonry in imitation of fine stonework and to mould into architectural decorations.
Rendering: The specialist craft of applying stucco across larger, flat and generally (but not exclusively) exterior surfaces.
Mention stucco, that indispensable and versatile building material, and many may think first of Renaissance Italy and, perhaps, of the finely detailed friezes of Palladian architecture. After all, while Andrea Palladio (1508-1580) built his reputation on his genius, he built his villas with stucco. A lot of stucco. For example, he constructed in stucco-clad brick rather than marble-clad stone and fashioned architraves out of wood, covered with straw lathing and, yes, stucco. His buildings remain fresh, invigorating and sound. And continue to fool their many visitors.
Stucco and the English Tradition
The conquering Normans used stucco in castles, cathedrals and, a little later, in houses. Stucco was here to stay but it wasn’t until the Restoration in 1660 and the golden period of Wren, Vanbrugh and Hawksmoor and English Baroque that Stucco re-asserted itself. As the century progressed, and neo-classicism came to the fore, stucco became an essential element of ecclesiastical, official and domestic architecture. Traditional stucco (render) was perfected between 1775 and 1850 and retains its basic mix of 6 parts sand, 1 part cement and 1 part lime. By the middle of the 19th century, four basic types of stucco (with further variations) were (and remain) in use.
This early stucco mix dates from the time of Inigo Jones in the early 17th century.
In the 18th century, patented versions emerged in which boiled linseed oil replaced water. The Adam brothers’ own blend was called Liardet’s Mix and used extensively in Portland Place.
This mix of naturally hydraulic lime with sand was developed in the late 18th century and was popular up to c.1850. Its rich brown colour is distinctive.
Just as Roman Cement Stucco was, like stucco in general, falling out of fashion, Portland Cement was developed and was widely used for decorative stucco. This hydraulic binder is made by firing clay and limestone together and grinding the resulting clinker with small quantities of other materials. It is now predominant across the world.
Mix and Application
Working with stucco – whether for a new build or restoration – needs specialist skills. First to achieve the precise, perfect mix; then to apply it to achieve an effective adhesion from the initial to the top coats and finally to execute the appropriate finish. Stucco is flexible and finishes can be smooth or patterned; stippled, gloss or matt; sand, marble, clay, lime wash etc..
The New Stucco: Acrylic Render
Stucco may be a traditional material, but it is just as relevant and equally applicable to modern and new buildings. And new mixes continue to be developed. Acrylic renders are now wide-spread. Their use is restricted to non-listed buildings and offer several advantages including improved water resistance, adhesion, flexibility and strength. They dry and cure in two days – traditional render requires 28 – and are suitable across a broader range of substrates including concrete, cement blocks, all forms of autoclaved concrete panelling and, with proper preparation, cement sheeting and the latest polymer exterior cladding.
Depending on type, they can be rolled, trowelled, sponged or even sprayed on and, like traditional render, take a variety of plain, patterned or textured finishes, matt, gloss or stippled.
Stucco Repair & Restoration
Whether the building is ancient, old or new, every element, be it traditional lime mouldings, modern cast ornamentation or render, is treated appropriately and expertly. That means identifying and replicating the original mix and applying it with equal precision and technique. Do check stucco regularly as once deterioration starts, it spreads rapidly and early intervention will reduce costs dramatically.
Precast and On-Site Replacement
When stucco deteriorates beyond restoration, it must be replaced. Large elements may have to be cast off-site while traditional forms (horse moulds) will be made for the on-site replication of pattern profiles.
Stucco is generally painted and, not surprisingly, when repainting is necessary, both broad traditions and the building’s specific history must, if the building is listed, be followed. If the stucco is part of a new, recent or unlisted building then a broader palette (including brilliant white) is available and can be applied using more industrial style methods.
Bespoke, precast stucco designs can also be fashioned for new buildings. Typical features for precasting include:
- Copings, balustrading and lintels
- Heads, cills and quoins
- Cornices, string courses and corbels
- Columns, pier caps and finials