Painting Lime Render – Everything You Need To Know
With all exterior decorating projects it’s crucial that you apply the right paint, but this is particularly true with lime render. Using the wrong paint risks trapping moisture, damaging the lime render and causing the paint to fail.
Our Technical Team often sees issues where lime render has been painted with the wrong product, which is why we have created this guide to help you avoid those mistakes and give you everything you need to get results even a pro would be proud of.
In this guide, we will cover:
- What lime render is
- Which paints are suitable for lime render
- Key considerations before painting
What Is Lime Render?
Lime render is a traditional form of exterior wall render, often used on older properties. Unlike modern sand and cement render, lime render is soft and generally erodes over time, creating a more natural, aged appearance.
Breathability is the defining feature of lime render. It allows water vapour to freely travel through an exterior wall. If moisture is unable to escape, it builds up within the wall and can cause serious issues.
Leading authorities on historic buildings, including the Society for the Protection of Ancient Buildings (SPAB) stress that anything that prevents the evaporation of moisture from walls will lead to difficulties. Common outcomes of trapped moisture include:
- Damp patches on interior walls
- Cracking and failure of the render
- Long-term structural damage to brickwork
- Colder, harder to heat walls
Flexibility is the other key benefit of lime render. Many older properties are not built with the foundations that properties have nowadays. This means that renders on older properties must be flexible enough to move slightly with the building.
If a hard, modern cement render is used, any movement will cause cracking on the render which must be repaired.
If you want to see how healthy your walls are, use our handy wall health check to spot issues early and keep your home stress free.
Why Paint Lime Render?
COLOUR
Probably the most common reason why you may be thinking of painting lime render is for a change of colour.
Painting exterior walls is the most effective way to add kerb appeal, which can add value to the property.
Paint allows you to add personality to your external walls, whether you want to opt for a crisp brilliant white or a unique pale pink that will make your home stand out from the crowd.
WEATHER PROTECTION
Lime render is soft and susceptible to weathering. While it is designed to naturally erode, the time may come that you decide that protecting the render and thus limiting any moisture ingress may be in your best interests, especially if you are suffering from damp.
Keeping walls dry also improves their thermal performance. Wet walls transfer heat much quicker than dry materials, as energy is directed to drying the external walls rather than heating the home. This makes damp properties colder and harder to heat effectively.
COST
Re-rendering is often the go-to when lime render begins to weather, but it comes with a high price tag. Rendering will easily cost well into the thousands, with the cost of labour and materials.
Paint can be applied yourself at home or by a professional decorator for a fraction of this, while also being less invasive on your home.
How To Paint Lime Render
Lime render is not compatible with all exterior masonry paints.
The breathable nature of lime render means that you must use a highly breathable paint, otherwise moisture becomes trapped and the benefits of lime render are lost.
The problem is, standard masonry paints are usually acrylic-based and are not highly breathable. When applied to lime render, they often aren’t able to release moisture quickly enough, causing damp problems.
Traditional solution: Limewash
For this reason, lime render was traditionally painted using limewash, a simple form of masonry coating that is made using a formulation of natural ingredients, commonly consisting of lime putty that has been watered down to create a thin decorative coating.
Having been around for thousands of years, limewash has been a staple form of paint finish on older properties and is still sometimes applied today.
The problem is that limewash offers no real protection. It allows moisture to soak into the wall and is designed to erode naturally within 1-2 years. While this maintains breathability, it does nothing to stop water entering the wall in the first place.
On older properties with solid walls and no cavity, that moisture can pass straight through into the interior wall. Over time, this can create damp conditions, encourages mould growth and accelerates the breakdown of the render itself. As it isn’t designed to resist weather, limewash typically needs to be re-applied almost annually.
Learn more: The ultimate guide to water ingress.
MODERN SOLUTION: NANO-TECHNOLOGY
To overcome the problems of limewash and standard masonry paints, silicone masonry paints like Emperor Masonry Paint were developed. It uses nano-technology to give lime render both protection and breathability.
The paint works by lining the microscopic pores of the lime rather than sealing them like a traditional paint. This means:
- Water cannot soak in because the surface becomes super hydrophobic and rain simply rolls away.
- Moisture inside the wall can still naturally pass through, because the pores of the lime render are completely open.
In independent tests conducted by a UKAS accredited laboratory found Emperor Masonry Paint reduced water absorption by 96%, while maintaining an SD value of 0.03. Any paint with an SD value 0f below 0.5 is considered breathable, with 0.03 being highly breathable and on par with limewash.
The result is that lime render stays dry, while still allowing moisture within the wall to escape naturally. The same independent testing showed that after 25 years of weathering, Emperor Masonry Paint continued to repel water and showed no change in appearance and no peeling.
As a result, lime render can be protected for decades while still retaining the breathability it needs.
Frequently Asked Questions
Will painting lime render stop damp?
If you are suffering from penetrating damp, painting lime render can help. It prevents rainwater from soaking into the walls, while not trapping it.
Over time, this reduces the amount of water held in the wall and allows it to dry out naturally.
Damp can also be caused by other sources of moisture, either through a defect, rising damp or condensation, which must also be fixed separately, as paint alone will not resolve them.
Learn more: The types of damp and what causes them
How do you prepare lime render before painting?
One of the most important aspects of any exterior painting is ensuring the surface is clean, sound and ready to be painted.
Unlike harder forms of render, lime render cannot be power washed down when cleaning it as this can damage the surface. Instead, you must soft wash the lime render or clean it using a hose pipe.
It’s recommended once large-scale dirt is removed to apply a fungicidal cleaner which will kill any green growth or other fungus that is attached to the external wall. This helps to reduce the risk of any fungus growing underneath the paint film that once it blooms, could cause it to lift from the render.
Once completely dry, clean and sound, you can then apply your chosen paint for lime render, ensuring that there will be no rain during the application process as this will cause problems.
If you have more questions about painting your lime render, our in-house team of experts are always here should you need us. You can reach them by emailing [email protected] or calling 01254 936121.
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This article was written by the Emperor Technical Team, a group of experts with an average of over 25 years experience in the building industry. They work daily with homeowners, tradespeople and specification professionals to deliver practical, expert guidance that promotes long-term results, supports wall health and helps create homes that are prepared for the future.
