In today’s economy, lime plastering or rendering is often more expensive than simply using cement or gypsum plaster. This is because the material cost itself has risen and because of their nature. Lime building materials require more aftercare than modern alternatives, and the labour cost is also normally higher. So inevitably, this begs the question. Why bother using lime plaster at all?
In most cases, lime plasters and renders outperform gypsum and cement alternatives. Lime plasters are more durable and they protect the substrate that they have been applied to. Many people think that because cement and gypsum plasters are often harder than their lime counterparts, they will last longer. This is not the case, typically the stronger the plaster, the less breathability and less flexibility they possess. Because of this, cement and gypsum plaster are often brittle and can crack and completely break down in as little as 10 years. On the other hand, there are examples of Egyptian lime plasters that have survived thousands of years.
Lime is an extremely versatile building material. There are almost endless possibilities when it comes to combinations of aggregates and additives to make a plaster exactly as you want it. Let’s dive into some of the other reasons why using lime plaster should be considered.
The Benefits of Lime Plaster and Render?
- Lime Plaster Creates a Beautiful Finish. When lime plaster has been used correctly, it can create an astonishingly beautiful finish. It’s possible to use lime plaster to create a textured or completely smooth finish. This will depend on the fineness of the lime and the aggregates used to create the plaster, and the workmanship of the plasterer themselves.
- Mildly Antiseptic Properties. Lime plasters use lime putty or hydraulic lime as the binder for the plaster. Lime is an alkaline material. This means it is mildly antiseptic and can help to kill disease-causing microorganisms. Lime plasters when used in combination with a limewash are an excellent way to combat mould growth.
- Creates a Breathable Surface. Almost all lime-based building products are breathable. This is especially important if your house was originally built with lime products. Breathability allows for trapped water to evaporate without causing damage to the plaster or substrate. Using gypsum or cement plaster can seriously damage old buildings and will cost much more money to repair than if you’d simply used lime plasters in the first place.
- High Flexibility, Perfect For Timber Framed And Older Buildings. Because lime building materials are often softer than modern alternatives, they tend to be much more flexible. Modern materials like cement are hard but brittle. When buildings move they can crack and begin falling apart. Lime plaster forms micro-cracks which can self-heal over time. This is a remarkable characteristic of lime and is a massive benefit to eco-buildings, old buildings and other buildings which require flexibility.
- Extremely durable. Lime building materials are known to be soft, so you’d expect they wouldn’t last as long as harder cement alternatives right? Well, because limes are soft, they protect the building better, allowing it to move and breathe without causing damage. There are examples of buildings constructed with lime still standing today after thousands of years. Most cement buildings are built to last 100 or so years.
- High workability. Lime’s high workability is a feature that is easier to feel when using it than describe here. Good workability allows for good workmanship and is the ability of the plaster to remain smooth and mouldable while it’s being applied. This is why plasterers often remark about lime-based mixes being a pleasure to use.
- Low thermal conductivity. This characteristic of lime indicates its mild insulative nature. In warm climates, lime plaster will feel cooler than a cement or gypsum alternative. In colder climates, lime plaster will feel warmer.
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How Long Will Lime Plaster or Render Last?
For a start, a quick overview of the difference between lime plaster and render. Lime plaster is used on internal works within the house. Lime render is used externally. Often lime plaster and render could be the exact same mix, the difference being one is used internally, and the other is an external finish.
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Because of this, lime plaster will of course usually last the longest. Good lime plastering can last centuries. By good lime plastering, we are talking about a well-mixed plaster with high-quality lime and sharp-washed sand. Click here if you aren’t sure what sharp-washed sand is. This plaster must then be applied correctly with good aftercare to ensure it carbonates fully, forming a strong bond.
The pyramids in Egypt were often plastered with lime plasters. This plaster has survived over 4000 years which is remarkable. Without these lime plasters, the ancient Egyptians pyramid texts and wall paintings would not have survived to this day. The ancient greeks and Romans also made good use of lime building materials, some of which are still standing today.
Lime render can also last for centuries, although this can depend more on how exposed the render is to the elements. A way to make lime render last longer is to regularly limewash it. Limewashing render can massively prolong its lifespan. Limewashing renders that face harsh conditions could be a good idea every year or two. ‘Free lime’ in the limewash can help to repair any cracks or damage on the render.
Related article: Can Lime Plaster Be Used In Bathrooms?
Should Lime Plaster or Render be Painted?
It is not completely necessary to paint lime plasters and renders. The finish lime building materials can produce is often beautiful by itself. Moreover, you can even use natural additives such as stone dust to help give lime plasters colour. For example, ham stone dust can be added to plaster, mortar and render to give it a warmer honey-coloured appearance.
Having said that, many people prefer to paint their plaster and render. With lime building materials it’s very important that the paints used are breathable. If they aren’t, you could expect to see your plaster and the substrate below the plaster damaged. Good paints to use with lime-based building materials include limewash, clay paints and other natural breathable paints. I would recommend limewash as it not only creates a beautiful finish but helps to protect the plaster or render it has been applied to.
Related article: Should Lime Plaster or Render be Sealed?