Earthen Plaster: An All-You-Need-To-Know Guide
When properties undergo major renovations, the developer or project manager will often strip the interior walls back to the studs. With the old plaster removed, it can be replaced with a fresh alternative.
Drywall plasters offer a quick and inexpensive alternative; however, with people wanting to reduce their effect on the environment, natural plasters are becoming more favourable. Despite drywall containing the recyclable material known as gypsum, when this substance is not disposed of correctly problems can occur. Since 2005, therefore, gypsum-containing materials have been banned from landfills in England. However, in America, millions of tonnes still end up in landfill sites.
Natural plasters are much more sustainable and are also proving more durable than drywall. With people spending more time researching environmentally-friendly alternatives, mineral and earthen plasters are seeing a revival.
What is Earthen Plaster?
There are three main categories of plaster: clay, lime and gypsum. Earthen plaster is a clay-based plaster that offers a healthy, more resilient alternative. Not only is it suitable for internal and external usage, it even lends itself to sculptures and relief carvings.
Earthen plaster may be a basic form of plaster, yet it is a particularly diverserve material that can create stunning interior wall finishes. It is incredibly adaptable to dying, creating a range of warming colours. However, it can also be manipulated for rustic, undulating walls as well as smooth finishes.
Using earthen plaster to create exposed, natural clay walls have long been a popular tradition in southwest North America, in states such as Arizona, California, Colorado and New Mexico. However, its popularity is spreading now in the northeast and further across Europe.
The History of Earthen Plaster
Earthen plaster has a particularly colourful history in traditional building construction around the world.
Within the UK, earthen plaster was used with lime until the end of the 19th century. Unlike building lime, earthen plaster’s materials were considerably cheaper and available in abundance. In most places, it was used as an undercoat, with lime plaster or limewash used in the same way as a plaster skim.
For the rest of the world earthen plaster, its history is a lot richer. Originating from the state of New Mexico, the tradition of enjarradoras developed. Villages identified their preferred location of plaster dirt, and methods of working with this dirt were passed down from mothers to daughters. Similarly in African countries, applying earthen plaster was considered women’s work. In fact, earthen plaster is still used to decorate their homes, creating cultural relief work and paintings called litema.
Unfortunately, with the introduction of cement, much of this knowledge was lost and sites that were known for plaster dirt have been forgotten. However, as earthen plaster provides a relatively cheap, sustainable alternative, it is making a comeback into modern building practices.
How to Mix Earthen Plaster
The base method for mixing your own earthen plaster is one part clay-rich soil to two parts sand; however, a form of fibre is required to add reinforcement to the plaster, enhancing its strength and durability. For earthen plaster, straw was a common addition, although animal hair, hemp fibre, bulrush fibre and coconut fibre are also used. As the clay dries out, the added fibre helps to counteract cracks forming as it provides it with some much-needed flexibility.
Another key ingredient is a form of additive. Additives are blended into the plaster concoction improving its overall strength, and often making it easier to work with. Depending on the project, these additives may only be applied to the mix for the final coat.
Common additives include:
- Flour paste
- Manure
- Milk protein (Casein)
- Linseed oil
- Ox blood
- And prickly pear cactus juice
Each additive adds its own unique benefits based on its constitution. For example, factors such as protein levels, fibres, enzymes, micro-organisms, pH level and minerals.
For dyed earthen plaster, all you need to do is add mineral pigments into the mix.
Earthen Plaster and the Prickly Pear Cactus
The prickly pear cactus is a part of the flowering cactus plant family, Cactaceae, and is native only to North and South America. What many people don’t know is the prickly pear cactus juice’s importance to earthen plaster.
When used as an additive, prickly pear cactus juice helps to increase the plaster’s set, making the mix stickier. However, before it dries, the cactus juice provides a natural binder to the aggregate (sand) enabling the plaster mix to be more manipulative.
The prickly pear cactus juice also provides a stabiliser to the earthen plaster. What this means is that the dried plaster becomes more water-resistant. This is possible due to the presence of pectin within the cactus juice. Pectin is a form of carbohydrate that serves as the binding agent, making the plaster more adhesive.
How is Earthen Plaster Used Today?
While earthen plaster gains momentum as a sustainable building material, it is often seen in museums and galleries on a global scale due to its key characteristics. Due to the plaster mix containing clay, it has an incredible ability to retain moisture. Consequently, the clay soaks up any moisture and prevents it from reaching the building’s structural materials. Museums and galleries are able to regulate their humidity levels, protecting all their artefacts and artworks by using earthen plaster on the walls.
The Advantages of Earthen Plaster
Despite earthen plaster being an older method of plastering, it has many advantages over modern drywall techniques.
As we have previously mentioned, earthen plaster is a much more sustainable material; it requires very little to produce and often contains a large proportion of recycled materials. Then, once it is surplus to requirements the clay can simply go back into the earth.
Similarly, its humidity-controlling properties make it a recommended plaster for bathrooms, basements and kitchens, rooms that experience variations in humidity and temperature. Furthermore, clay acts as a thermal mass – retaining heat within the daytime and using this to heat the room into the evening, and similarly absorbing coolness during the summer nights, to regulate the day’s temperature. This natural heating and cooling system help improve a room’s energy efficiency rating, saving money for some.
In addition, earthen plaster is less toxic and helps to filter the air in the room. It achieves this as this clay-based plaster does not require painting, reducing the need for paint containing harmful VOCs (volatile organic compounds) to be applied on top. It is healthier still as clay is naturally resistant to mould and mildew, helping to keep the room fresh.
The only real downside to earthen plaster is its application. The materials may be significantly cheaper; however, it takes a much longer time to apply. Each layer needs a lengthy drying time, which is arguably why many builders are sticking with more modern processes.
Alternative Plaster Options
If earthen plaster isn’t for you, there are other popular types of plaster available in the UK. As we mentioned earlier, plaster falls into three main categories: clay, lime and gypsum.
Lime Plaster
Lime plaster is another type of natural plaster. Instead of mixing clay with sand, fibre and additives, the calcium-containing mineral lime is used. This substance is high in oxides, hydroxides and calcium. Its materials make it extremely resistant to the elements; therefore, it is often recommended for external plastering.
It is proving to be another environmentally-friendly option for builders and plasterers. Currently, the cement industry equates to 8% of all global carbon dioxide emissions. However, when lime plaster hardens, it begins to transition back into limestone, and in this form, it is able to reabsorb carbon dioxide from the earth’s atmosphere.
Additionally, another advantage of lime is its alkaline pH reading. Being highly alkaline provides it with antiseptic properties, including antibacterial and antifungal.
Gypsum Plaster
Gypsum is a common sulphate mineral that is currently used in the majority of plastering, including drywalls. It is less environmentally friendly in a plaster form; when incorrectly disposed of, harmful chemicals can be released into the atmosphere.
When a POP powder is made into a paste with water, it can be applied to most surfaces, including brick, solid or hollow blocks, plasterboard and concrete. When it hardens, it is recognised as gypsum plaster.
Despite its environmental concerns, it has many benefits for plasters and builders. For contractors, gypsum plaster is extremely easy to work with and can be applied in a fraction of the time of other types of plaster. Additionally, as gypsum produces less heat, there are minimal to no shrinkage cracks in comparison to traditional cement plaster.
Furthermore, it has insulative properties and is fire and impact-resistant, making it a compliant material for building regulations.
Choosing the Best Plastering Solution for Your Property
For those considering re-plastering your property or looking to plaster a new build and are after an environmentally-friendly and sustainable material, earthen plaster is worth your consideration. However, there are plenty of other readily-available solutions on the UK market for you to choose from. Some of the factors to take into account include the type of property you are working on, the climate conditions, specific building regulations, any time constraints and your budget.
Need advice? If you are unsure about which plaster is suitable for your property, get in touch with the experts at AB Drylining. Our teams are extremely knowledgeable; they are CSCS certified, as well as PASMA and IPAF accredited in providing professional plastering services to commercial clients.
