A Soft Touch and A Warm Glow
Natural Plasters have been used for centuries to finish both the interiors and exteriors of homes, bathes, and just about any building. Using locally available materials, people around the world have been able to create stunning finishes that not only beautify a space, but also help to protect the walls from wear and weathering.
A finish used on the interior of a building is most often referred to as a plaster, whereas those used on the exterior are called renders and would often include some form of sealant or an extra ingredient to help better protect against weather. The most commonly used renders are lime based.
Natural Plasters are the perfect compliment to any natural building and are a great addition for conventional home owners who wish to incorporate some natural elements in their built environment. They can be as creative as any imagination or simple and classic. Talk to one of our members about how you can incorporate Natural Finishes in your home.
Natural Plasters are by no means limited to being applied to just natural walls, they can just as easily and effectively be applied to almost any wall surface. The difference in applying Natural Plasters to natural walls vs. conventional walls is all in the preparation of the walls. That said, we would never recommend finishing a natural wall with a conventional product. Doing so would not only cause serious risk of damage to your walls, but it would also greatly decrease the health and environmental benefits achieved with the natural walls.
Wall Prep on Natural Walls
To prepare for a Natural Plaster on natural walls, such as Strawbale, Light Clay Infill, Cob, Earth Bag, Clay Wattle, or Wattle & Daub, a base coat must first be applied over the “guts” of the wall. This base coat is often referred to by many names, including: “brown coat”, “scratch coat”, and “levelling coat”. Though the main components of the base coat are virtually the same as for a finish clay plaster, the specifications vary in the refinement of these components. The base coat is usually a minimum of ¾ of an inch thick, whereas a finish clay plaster is usually no thicker than ¼ of an inch in thickness. A good rule of thumb here is: the thicker the application, the bigger the size of the components.
Wall Prep on Conventional Walls
To prepare for a Natural Plaster on a conventional wall, such as drywall, an adhesion coat is needed to ensure there is a good bond between the wall and plaster, and to make application of the plaster easier. This is easily achieved by rolling on a flour paste and sand mixture. Although this technique is sufficient in most cases, some conventional walls need a bit more preparation to make sure the plaster is not going to discolour or crack. Depending on the material, a primer that will seal the components of the wall off from mixing with and contaminating the plaster may be advised. As well, burlap or another mesh will help safeguard against cracks when spanning across a gap, seam, or two different materials. This last safeguard also applies to the seams between natural walls and wooden framing members.
Composed of clay, sand, fibre, flour, and water, clay finishes are quite simple to mix up. The exact recipe will depend on the materials available as well as the desired outcome. The thickness of the finish is easily varied to accommodate for different requirements and designs. Anything from ¼ of an inch down to a thin clay paint, called an Aliz, is typically used, though thicker can be achieved when needed.
Clay finishes can be used just about anywhere, from garden walls to bedroom ceilings, the application of clay plasters is just about endless. Living rooms, bedrooms, entryways, all of these benefit greatly with the application of an alluring clay finish. Adding a softness and texture not found in paints, clay finishes can turn a room into a warm and engaging space.
The clay used in a clay finish is the main influence over base colour, followed by the colour of the sand. A white clay and sand is usually chosen for the base of a clay finish, as lighter coloured walls are typically more appealing than darker ones. If starting with a light base, it is much easier to adjust the colours with pigments, while a darker based plaster will see little to no difference with the addition of pigments. Some places have very beautiful clays available naturally and are applied with no colour added to some lovely results.
The selection of colour for a clay plaster is quite large and it is easier to ask about a colour you want than for us to list all that are available. We do keep samples on hand to help give clients a starting point when it comes to making this decision. Our plasterers are quite skilled at colour mixing, it may surprise you to see what is possible. Keep in mind however, that there is a saturation point when it comes to the addition of pigment in a plaster. If you find that a more intense or rich colour is wanted, an aliz or pigment wash can help in achieving this.
The texture of a clay finish is another area that can be played with. Anything from a spackled surface to a highly polished and smooth finish can be achieved. Besides physical texture, various additives, such as chopped straw and mica, can add a more subtle and soft visual texture.
As a Render
To use a clay based plaster for the exterior of your building proper protection from the elements is needed. Usually a minimum of a two foot overhang is required for good protections, though you will want to monitor the direction the rain falls in your specific location. If strong sideways rains are typical, then either a larger overhang will be required, or one of many resistance helpers or sealants.
The following list includes many of the additives that may be used to make a clay render more weather resistant:
- water glass
- linseed oil
- glue wash
- cow manure
- horse urine
- cactus juice
- xanthum gum
Some Hidden Pros of Clay Finishes
Clay plasters help clean the air! There have been a couple of studies done (that we know of) that have measured the levels of pollutants pulled from the atmosphere by clay plastered walls. The results were quite inspiring, stating that clay-plastered drywall “effectively removed 88% of the ozone.”
Clay plastered walls also add some mass to walls, which absorbs and holds the heat of the sun. Using thicker clay plasters opposite windows can help reduce heating bills by storing the sun’s heat and releasing it back into the room.
Where Not to Use Clay Finishes
The most important thing to know is that for a clay finish to function properly it needs to either stay dry or be able to dry out relatively quickly. Therefore, there are a few places where clay finishes are not highly recommended. These include rooms where the walls are consistently exposed to medium to high levels of moisture, such as a bathroom or wet sauna. The kitchen is another place where clay is less advised. This is less due to moisture issues and more due to the ease and frequency of cleaning. Clay finishes aren’t designed to hold up to a good scrubbing, and the oils from cooking can stain an unsealed clay finish.
Lime finishes are composed of lime putty, sand, and optional colour pigments. We are lucky here, in the Cowichan, to have type S lime available, which is one of the easiest limes to work with. Though it may seem like a simpler mix than clay finishes, lime plasters require a more specialized training as the plaster is less forgiving and more time sensitive.
Lime plasters are best in layers, with two coats as a suggested minimum, and three as best practice for renders. The build-up of layers, each with a consecutively greater lime to sand ratio, creates a more durable and solid final product.The hardiness and durability of lime plasters really save the day where clay finishes fall short. Perfect for wet areas and able to stand up against a good scrubbing, lime plasters work well in bathrooms, wet rooms, kitchens, and as renders.
Lime is very white and is only slightly influenced by the colour of sand used. Adding pigment to a lime plaster offers a nice array of colour options in more of a pastel category. To achieve more vibrant colours frescos and washes are used.
- A fresco is achieved by adding diluted pigment to a partially set (dry) lime plaster. The most famous fresco would have to be the Sistine Chapel ceiling by Michelangelo done in the early 1500’s. As evidenced by this, frescos really hold their colour over time and great detail can be achieved.
- A lime wash is highly diluted lime putty with optional pigment. A wash can be applied at any stage after the lime plaster has set. This is a great way to achieve colour after the walls have been plastered, freshen up the plaster, and maintain a high level of integrity of a lime finish.
As with a clay finish, a variety of textures, from rough to smooth, can be achieved with lime plasters. Hemp is used in place of straw as the silicas in it hold up to the alkalinity of the lime better than those in straws.
The smoothest lime finish is a process called Tadelakt. The mix for tadelakt is slightly different and the amount of work involved is quite a bit more, however, you are left with a nearly completely waterproof surface. Tadelakt originated in Morocco, where it is used extensively in both their bathes and their homes. Here, Tadelakt is a great natural alternative for showers and sinks and is a magical addition as a feature aspect on a wall or even a stand alone finished sculpture. If you are really ambitious tadelakt can be used on all your walls. The only place we don’t recommend using tadelakt is as a kitchen counter, though an earthen counter does work well (please see Creative Ideas to learn more about this).
As a Render
Lime is a very effective render as it is extremely durable and can withstand direct weather impact. Still, sometime cow manure or cactus juice is added to increase its performance. When using lime as a render three coats is highly recommended.
Some Hidden Pros of Lime Plasters
Although lime undergoes quite an energy intensive process to be created, once applied and let to set it re-absorbs CO2 and slowly returns to its original limestone state.
If a lime plaster cracks it is not ruined. The periodic application of a lime wash heals and repairs these cracks quite easily.
Lime is naturally resistant to moulds and mildews. It is a great replacement for grout in tile work that will not grow that nasty mildew.
The Challenges of Lime Finishes
Lime needs to cure, not dry. Fresh lime finishes must be protected from winds and sun for at least a week, as well as not being subjected to temperatures below 4.5 Celsius. Misting the plaster throughout the day will help keep the finish from drying out.
Lime is extremely alkaline and can burn the skin. Protective eye-wear is always recommended as well as rubber gloves and long-sleeved clothing. Keeping vinegar on hand to counteract the alkalinity of the lime is a great safety measure as well.
Lime finishes tend to take more time. Unlike clay finishes that are done after one finish coat, lime is best with two to three coats, adding to the application time.