Tag Archives: lime

Why Use Lime-Based Renders?

An Introduction to Lime

The use of Lime in building materials has a long history, dating back to the times of the Roman Empire, when lime was used for construction purposes such as mortars and render finishes. It continued to be used until the nineteenth century until Portland Cement and other cements came onto the scene, when the use of lime-based materials began to decline.

Lime is still frequently associated with vernacular buildings within areas in the south of England along The Jurassic Coast, and in places such as Bath and the Cotswolds. Lime has also recently experienced a bit of a revival in modern building and construction for use in modern renders.

So why would you want to use lime as a component in your render finish for your EWI system?

The Use of Lime in Building Materials

Lime is considered to be a ‘healthier’ building material in comparison to Gypsum and cement-based products. This is because quicklime absorbs carbon dioxide during the setting process of carbonation – otherwise known as the lime cycle. Essentially, the lime cycle is the hardening process of lime mortar and lime wash when water evaporates from lime putty and the lime reacts with the carbon dioxide present within rain water.

During this repeated cycle, the lime experiences a repeated chemical change until finally it is converted back to calcium carbonate (which is basically the original limestone). This is a slow process, but essentially what this means is that your lime mortar will eventually get stronger as time goes by. This process creates the oldest and most flexible and breathable form of lime.  

Another reason that lime is frequently used in mortars and building materials (e.g. our Lightweight Basecoat) is due to the fact that lime is a caustic. This primarily means that it has disinfectant qualities – lime mortars, renders and washes have been used to create hygienic and comfortable surfaces for buildings for thousands of years.

Lime can also be produced on a small scale; it can be produced in small quantities to meet primary demands, therefore saving energy and resources. With reference to the use of lime in the Roman era, and the gradual hardening of lime during the lime cycle – lime-based renders are also durable and have historically stood the test of time, which means that reproduction of materials for repairs is less necessary. It’s therefore a favourable option for those who are environmentally conscious but also want a durable render facade.

Lime-Based Renders and EWI systems

Lime as a component in building materials adds the benefit of breathability and vapour permeability; the greater the amount of pure lime in the building materials, the better the breathability. Because lime is porous, it absorbs and releases humidity (it breathes), therefore helping to maintain the thermal comfort of a building. This makes it fantastic for older buildings by allowing the building to breathe, and also in external wall insulation systems.

Lime-based render is an excellent addition when used in external solid wall insulation systems. This is because the breathability of lime means that it can prevent ingress of moisture, which as we know would disrupt the effectiveness of the system. This is because any kind of moisture content prevents the insulation material from retaining heat properly.  

Due to its small particle size, lime can fill minute voids within a surface, which makes it a great adhesive in comparison to cement which has large particles. Due to this, lime also binds gently to background materials, allowing for flexibility and crack resistance – although lime-based renders are more likely to develop fine, hairline cracks in comparison to larger cracks within cement-based renders.

When installing lime-based render, it cannot be applied during freezing temperatures, as this will delay the carbonation process and the render can take up to a month to properly set which may cause the render to fail. Lime-based render must also be treated with a breathable finish such as lime wash or silicone paint to protect the underlying render.

Looking for more information? Here are a couple of blogs all about when a basecoat that contains lime would be ideal…

‘Applying Coloured Render to Thermalite Blocks’

‘Sand and Cement Render on High Performance Blocks’

Stay tuned for more blog content! We upload every Tuesday and Thursday all about our EWI and render systems, answering FAQ’s and giving full and detailed product guides.

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EWI-269, lime basecoat, lime render

Why use a Lightweight Basecoat?

We are excited to introduce one of our new products for our lime based range, the EWI-269 Lightweight Basecoat! Our Lightweight Basecoat is intended for use in render-only systems as a finish on properties with high-performance blocks such as Ytong, Poroton and Porotherm. The main intention of the Lightweight Basecoat is that it is a one-coat, breathable basecoat, used to level the substrate before being finished with a coloured render.

In this blog, we are going to properly introduce our new product to you and talk a little bit about what it’s for, what it does and why you should use it!

Why use a Lightweight Render System with AAC blocks?

Take for example AAC blocks (autoclaved aerated concrete) such as Ytong. These are produced from autoclaved lime, sand, cement, water and a rising agent. AAC blocks are high performance because of their thermal and acoustic insulation capabilities. They are more environmentally friendly and offer higher fire resistance than the common bricks and mortar.

The reason you would want to use a Lightweight Basecoat with AAC blocks is because these blocks tend to be a lot softer. AAC contains 60%-80% air, indicating a high insulating capacity and a softer substrate. If you were to apply a completely solid cement mortar over the soft AAC blocks, there would be an increased chance of cracking due to incompatibilities in the strengths of the cement mortar and the AAC blocks. A cement mortar would also negate the AAC blocks ability to breathe.

This is why you would use our Lightweight Basecoat. Both AAC and the Lightweight Basecoat are lightweight, soft and breathable. Therefore, when used together the chances of cracking are minimal and functionality is optimal.

The Lightweight Basecoat and Lime

Our new Lightweight Basecoat contains a key ingredient, lime.

Lime has been used in building and construction for thousands of years, it is a truly tried and tested building material in the UK and is proven to stand the test of time – you might have noticed certain areas in the UK (e.g. Bath) where vernacular buildings are made with lime.

Lime as a component in building materials (such as in our Lightweight Basecoat) adds the benefit of breathability. We talk a lot about breathability here at EWI Store, and essentially it means the buildings’ ability to transmit moisture. If a building is not able to expel moisture and water vapour, then damp can occur internally and externally. This can cause damage to the building structure and can also pose a health risk due to poor indoor air quality.

For these reasons, it’s incredibly important for a building to be able to breathe, which is why using our Lightweight Basecoat on breathable AAC blocks provides the perfect combination for allowing this function. 

Furthermore, insulation and breathability go hand in hand. Humidity and moisture can severely disrupt a buildings’ thermal performance. Because the lime within our Lightweight Basecoat is porous, it absorbs and releases humidity (it breathes), therefore helping to regulate humidity and maintain the thermal comfort of a building.

Applying the Lightweight Basecoat

The Lightweight Basecoat is applied in a very similar way to our other basecoats. It comes in a 25kg bag and is simply mixed by hand or using a mechanical mixer with 5 litres of clean, potable water.  It is then applied to the substrate by spray machine or by hand using a plastering trowel. Fibreglass mesh can also be embedded within the basecoat. The only real difference in application is that because it’s so lightweight, this basecoat can be applied up to a thickness of 25mm.

Because it’s a simple grey colour, once it has set it will need finishing with a decorative render. It’s essential that a breathable render is applied on top of the Lightweight Basecoat, so we recommend using either our Lime Render (coming soon!) for a smooth finish, or for a textured finish use our Mineral or Silicone renders. These are all highly breathable and are through-coloured, so will offer both an attractive and high performing finish.

Lightweight Basecoat – An Overview

  • Highly breathable.
  • Crack resistant.
  • Can be applied up to 20mm thick in one pass.
  • Perfect for new build properties.
  • Works well with AAC blocks – Poroton, Porotherm, Ytong.
  • Can be primed and painted with a breathable render finish.
  • Has a thermal conductivity of 0.47 W/(mK).
  • Internal and external use.

Lightweight Basecoat available for order now!

Order by phone or online! We hope this was useful and provided clarification about our Lightweight Basecoat but if you have any more technical questions, give us a call we are always happy to help!

Stay tuned to our blog! We upload new content every Tuesday and Thursday all about EWI materials, technical advice and more.

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