The Art and Practice of House Rendering in Wales

House rendering is the art of overlaying a building's exterior with a layer of plaster mixed with various aggregates. This practice has left a significant mark on the geography of Wales, providing a combination of pollution levels, ambient temperature, and precipitation.

Oct 22, 2024 - 23:37 Updated: Oct 22, 2024 - 23:38

House Rendering in Wales

A basic introduction to house rendering is offered before investigating the craft production of house rendering. House rendering is the practice of protecting and decorating the external wall surfaces of buildings using layers of render, which are mixtures of plasters with various aggregates. 'Rendering' is a term often encountered in discussions about buildings. However, rendering in the present is usually seen as an inferior pastiche of earlier craft practice in response to technological failures that arise from underestimating the effect of air corrosion upon building systems.

This study explores the art and practice of house rendering in Wales at the village level as craft production. The layer of render must both be resistant to the effects of precipitation and be decorative to convey information about the ideology, function, and use of the building it is applied to. This decorated render layer is variously coloured with natural mineral pigments, which have shown strong resistance against the effects of acid rain. Therefore, the skill with which the render is built up is essential, allowing great skills to develop in applying aesthetic render finishes. Understanding traditional house rendering is vital in establishing the principles that defined the various materials, techniques, tools, and ornamentation that developed in the different regional rendering styles across Wales. It also provides an appreciation of the materials and techniques that continue to allow existing traditional renders to be protected while still being repaired.

Traditional and Modern Techniques

House rendering has been used to protect homes all over Wales for over two centuries. It has evolved from the simple limewashing of walls to an intricate series of traditional and modern techniques that characterize the craft in various country regions. Traditionally, the method used has been dictated by the availability of materials and was heavily influenced by the local style of architecture at any given time. For many years, people worshipped in timber-framed churches with wattle and daub walls. The same formation was used for dwellings with the basic frame filled in with various readily available materials. In more modern times, using rubble stone to infill has become fashionable. Mixed with clay, the stone became a cob, and the Welsh cob could be found in huge lumps between the walls of cottages. As previously stated, the exposed cob homes were generally limewashed to protect them from the harsh weather. By the late 17th and early 18th centuries, cob was concealed with a skinny coat of lime plaster. As styles developed, there were many regional differences in methods and finishes. Nowadays, cement and plastic paints are generally more popular for rendering and painting, but some people still maintain the traditional fashion. Over the period, various methods of external wall covering have been used in Wales. The makers of these coatings were considered artisans, and knowledge was passed down through the generations. Nowadays, the vast majority of homes in Wales are mortar plastered, but the materials used and methods installed are very different from those used in matching original 'half-timbered' homes. Modern techniques vary in the type of material used, including paint-on, dash coat, thin coat sprays with a machine, and tip-on-side in situ. Advances in technology have brought about the use of rendering rasp, synthetic render beads, and grouting bags. As such, the skill or person producing the final coat or finish is generally more accessible for a more significant number of people to master. This is not meant to imply that the art of finer flowing walls is not appreciated. These are now usually considered for restoration projects or homes.

Materials and Tools Used in House Rendering

The choice of materials for house rendering varied and differed from area to area. Those choices contributed to the textural identities of different places and the sequences of buildings that are visible in settlements up and down the land. The main components of a traditional lime render in Wales were lime and sand, but other materials could also be used, such as ash, heather, blood, and ox-hair. Lime has a number of different material properties, and these contribute to its aesthetic qualities as well as to its long-term durability as a coating for walls. Lime is also associated with typically Welsh render design, as Welsh building customs are suited to its properties, and most older buildings were designed to be rendered with lime materials. Appropriate materials for house rendering will also be durable.

For applications that have additional demands to be waterproof, the formulation of natural hydraulic limes and Portland cement, in various combinations with several silicate materials, can also meet these demands. The traditional materials for rendering were specially formulated to improve the durability of stonework on elevations. To protect the stonework and mortar from the weather, the render usually over-sailed the stonework and sloped away from it to ensure that rain never lay on the stone table. Thus, render can protect the building from penetrating dampness caused by wind-driven rain, and it also protects the relatively soft sandstone. Some houses either have or were designed with cement renders, which have different needs from lime materials, and these will be discussed as well. Alternative synthetic render materials have also appeared on the market in the latter half of the 20th century, and we can get away with using one of these and still be faithful to the Welsh vernacular if the materials had been available at the time that the render in need of attention was applied.

The places that require a good finish with commercial sand and cement are very few and far between in the mountainous, upland, and coastal areas of Wales. There are many different tools designed to support specific techniques and materials available because it is essential for the tradesman to make the task as light as possible. Some methods are traditionally used with trowels, and other tools are called in to support the final appearance of the wall. Not all of the tools of the trade are absolutely essential; adaptive methods will be adapted depending on the context of the work. Scaffolding is preferably used for most work due to the precision that is required. If the work is on an old-fashioned Welsh cottage and the source wall is solid stone, consider the use of an electric mixer, as the walls are very out of plumb, and the render coat is only skinny, and it will be faster than putting in the work. If you are using a handheld mixer, then use half the water initially and then gradually increase to avoid mixing too thin. For cob walls, you will need to source the cob mix and proportions for the coat layer. Do this as described for the sink coat. The same considerations for the mix should be applied, and the scratch coat should support the positioning of the base coat. Therefore, the mix should be cohesive yet well designed for the provision of bearing for the base coat.

Challenges and Considerations in House Rendering

House rendering can confront us with a range of quite different and mutually challenging environmental conditions, including falling and driving rain, high humidity, and occasionally high wind pressure. The first problem we encounter when we prepare the surface for rendering is to ensure that the substrate is dry enough to permit decent adhesion and to allow the render to dry out correctly. Drying times prior to and after rendering can be particularly critical in rendering exteriors under certain climatic conditions. The drying process can be retarded by a moisture content of the substrate that is too high or by high humidity. Sometimes, there are significant enough diurnal temperature changes to cause condensation of that moisture on or just below the surface, leading to a family of problems that may arise or for the diurnal and seasonal differences to be sufficient to cause the render to spall off or other forms of distress over time. Another crucially important aspect of surface preparation is the assessment of the condition of the substrate. The first task a renderer has to deal with is familiar and rather mundane. In order to get a good finish, the substrate needs to be flat and even, so prepare the surface for the render to achieve something that will last. Poor surface preparation can lead to all sorts of problems and unsightly imperfections. Poor adhesion can be a consequence of a lack of keying or a bonding agent, for example, or can arise from causes such as impeded background adhesion due to cement paste, dust, or efflorescence. There are other imperfections that can result in defective renders. The single most common problem resulting from poor artistry is cracking. This is a common and potentially occurring defect in renders, and outside of the issue of retaining heat, it may be the most important. This is especially true of cracked finishes or internal walls. Commonly, the cause of cracking is thought to be poor supervision on site, inadequate preparation, insufficient keying and mixing, and insufficient curing. Yet, the most likely cause is none of these but the physical properties of the render itself. Indeed, whether the reason for the crack is economic and need not concern us, the cause of the cracks will nearly always be inherent to such practices.

Regarding render finishes, calculations must be made concerning the system used, allowing for such properties as initial adhesion, shrinkage, and render weight. For example, if you can achieve a design adhesion strength of 2.5 N/mm², it should be appreciated that on the ground floor wall, over an area of 1m x 1.26 metres, a positive load of 600 Newtons may be needed to pull the render off the wall. Considerable care is always required in the design. It is always necessary to check what new products or practices may need consideration when favouring the traditional or the traditional appearance. This is particularly the case concerning new regulations concerning fuel and CO2 emissions. Of fundamental importance to the system's performance are the requirements in terms of artistry, which should not be too hard to find.