Lime render is a traditional exterior coating that originated before the modern coating techniques of the 20th Century and is made via a mix of lime putty and sand. This render is suitable for naturally sourced materials such as natural stone, terracotta, brick and cob. It is an eco-friendly construction material and is mostly used today for conservation and renovation of historical and traditional properties and monuments.
The following information sheet will answer 12 common questions about Lime Render:
1) What is lime?
2) What is lime render?
3) What does lime render do?
4) What surfaces is lime render suitable for?
5) What surfaces is lime render not suitable for?
6) What is Lime Render best suited for?
7) How long will lime render last?
8) Are there any environmental, historical or geographical considerations to do with Lime Render?
9) Are there any common problems with Lime Render?
10) What are the coating options if I have a Lime Render exterior?
11) How do I apply a coating to Lime Render?
12) What are the colour selection options for Lime Render coatings?
What is Lime?
Lime is among one of the oldest and most vital materials used by humans and the products are more in demand today than ever before in history. In construction, Lime is the base product widely used to produce mortars, plasters, and lime washes for traditional buildings. The word ‘lime’ refers to products derived from burnt limestone. For example, products such as quicklime, hydrated lime and lime putty.
Limestone is a naturally occurring and abundant sedimentary rock which consists predominantly of high levels of calcium and/or magnesium carbonate, and/or dolomite (calcium and magnesium carbonate). Limestone also contains small amounts of other minerals. It is extracted from quarries and underground mines all over the world.
Even after processing, products made from limestone have the ability to return to their original chemical form – this is called the ‘The Lime Cycle’. Burnt limestone creates quicklime, and adding water to this creates hydrated lime. At either of these points, if left untreated, carbon dioxide in the air can react with the lime products and convert it back into limestone. The time taken for quicklime/hydrated lime to convert back can span from less than an hour in industrial processes or several years in atmospheric conditions.
Lime putty (non-hydraulic lime and another lime product) is produced by burning relatively pure limestone between 850 and 1,300 degrees C. The resulting calcium oxide is slaked in clean water to produce lime putty (calcium hydroxide). This form of lime cures (carbonates) by absorbing carbon dioxide and then reverts to calcium carbonate. Lime Putty is usually stored under water to prevent it curing prematurely.
Lime putty is not used on its own. It is the binder where the putty is mixed with suitable sand in the correct ratio to make a lime mortar, lime render or a lime plaster. Lime putty can also be watered down to make a lime wash.
What is Lime Render?
Lime render is a traditional exterior coating that originated before the modern coating techniques of the 20th Century. It is made via a mix of lime putty and sand.
Traditionally, lime render was applied to give protection to walls built of poor quality rubble, stone, porous brick or walls in exposed locations.
As an exterior substrate, lime render will always need a top coat of either a traditional Lime wash or the newer, and more durable, mineral paint. Both of these coating options bond to the substrate and provide a protective outer coating for exterior walls.
What does Lime Render do?
As an exterior coating, lime renders act like a sponge- absorbing rainfall and then allowing it to evaporate rather than soak into the wall. Lime render is therefore considered a breathable coating.
Lime render has distinct advantages over cement based alternatives:
What surfaces is it suitable for?
A lime render is a traditional building technique that occurred before the modern building of the 20th century. Therefore, this render is most suited to naturally sourced materials such as:
Today, lime render is commonly used in the conservation of old and traditional buildings that originally used lime mortar and materials.
Lime render is rarely used in new constructions. However, new technologies applied to lime materials mean that it is possible to enjoy the look, feel, and durability of a traditional render finish with a more durable modern performance. However, we recommend talking to a professional if you desire this type of finish.
What surfaces is it not suitable for?
What are its best uses?
Today, Lime render is mostly used for conservation and renovation of historical and traditional properties and monuments. This is because most modern building techniques are not viable for a Lime rendered building.
How long will it last?
If coated correctly, a lime render can last many years. However, the durability is all dependent on the exterior coating applied.
Limewash Coating: If applying a limewash to your lime renders exterior walls, then this will have to be recoated every few years. Failure to do so will result in the eventual failure of the lime render.
Mineral Paint Coating: For a more durable option - we highly recommend a coating of Mineral Paints on your exterior walls. Due to the permanent bond of the mineral paint to the substrate, Mineral Paints create an extraordinarily durable finish. This is due to the paint becoming an integral part of the substrate. Some buildings in Europe have even lasted over 100 years without needing a recoat by using this fantastically durable coating.
Are there any environmental, historical or geographical considerations?
On the whole, Lime is a traditional and environmentally-friendly building material. Lime renders and lime materials all are made from the natural resource limestone. Although this is sourced through mining, the environmental production costs are minimal when compared with other exterior coatings. Furthermore, Lime reabsorbs Carbon dioxide when it sets, it is recyclable and biodegradable. Lime render is suitable for eco-builds.
If you are considering recoating or reapplying your lime render, then thought must be given to the historical and geographical considerations that may affect your property. If your house is an older building, always ensure correct regulations are followed when doing any renovation and any building listing considerations are followed.
Furthermore, certain regions of the UK can have different regulations and advice to do with the renovating of properties. Ensure you check with your local council for any statutory guidance you may need to follow.
Are there any common problems with Lime Render?
Older buildings coated with lime render can suffer with damp problems. The trapped moisture can cause:
The moisture seeps in from a damaged exterior coating and gets trapped between the coating and the wall. If left untreated, this can cause serious structural and aesthetic damage to the property.
Additionally, due to the porous nature of lime render, if the render does fail this can cause:
Furthermore, in very damp lime render substrates damage can be caused by migration of soluble salts. These salts can crystallise and damage the masonry under the force of crystallisation within the substrate pores.
Another problem to watch out for is the inappropriate renovation and repair of lime render. Some traditional and historical buildings have been repaired and renovated using inappropriate coatings made from impermeable materials designed for modern buildings. These methods and materials use completely different construction methods and can result in worse damp problems and damage to the structure.
If an inappropriate render is applied on top of a pre-existing Lime render, moisture will not evaporate effectively and thus will become trapped. This can cause; damp, cold walls, condensation, flaking paint, rotten joists and other timber fittings, increased heating bills, dampness on interior walls and in extreme cases structural damage.
However, it is important to note that materials and techniques used for repair and redecorations need to be suitable for the age of the property and take into consideration the lime render surface.
Before correcting any problems with your Lime Render, we always recommend contacting a professional.
What are the coating options if I already have Lime Render?
Due to the nature and properties of lime render on traditional and old properties, many of the modern coating options are not suitable. Therefore, selecting the right material to achieve a protective and permeable coating is vital.
Hard cement renders and many masonry paints are not suitable for use on older and traditional buildings that have been coated by Lime Render.
It is vital that the coatings of these older and traditional properties allow the moisture that is continually being absorbed into the building to evaporate easily. Buildings that utilise Lime Render exterior will need to have a breathable exterior coating.
It is very possible that if you have a Lime render house then you probably already have an exterior coating of Limewash on the exterior of your property. Limewash is a traditional coating which provides a breathable, decorative finish that soaks into the underlying substrate to which it is applied. The material is made of slacked lime (calcium hydroxide and sometimes with other organic additives.
As a coating for lime-based render, limestone and stucco, limewash is in many ways comparable in nature to that of the underlying material with a similar porosity, PH value and coefficient of thermal expansion. Limewash is generally applied and used for historic buildings.
However, if Limewash is applied it will need recoating every few years to maintain efficient protection for the underlying render, substrate and property. Limewash can be applied by professionals or the homeowner depending on scale of building and skill.
However – There is an alternative to Limewash to coat your Lime Render! On lime render, we highly recommend you consider a Mineral Paint coating.
A mineral paint is a masonry coating that creates a bond with the underlying mineral substrate. This is different to conventional oil based paints and masonry paints, because rather simply forming a surface film coating, Mineral paint becomes an integral part of the substrate through creating this bond.
The bond between the paint and substrate is a chemical bond, rather than a psychical bond, and is called Silicification. Silicification is a chemical reaction between mineral surface, filer and the potash water glass and thus no surface film is being produced. Instead, a silicified, micro-porous unity of surface and coating is created.
Mineral Paint is perfect for Lime render as it bonds in a similar way to limewash but without the need to recoat every few years. Mineral Paints remain highly porous, breathable, and doesn’t damage historical or traditional buildings.
Furthermore, mineral paints are far more durable than your average masonry paint and far surpass the durability of that of a Limewash. See our information sheet on Mineral Paints for more information on this coating.
How do you apply a coating to Lime Render?
Check substrate suitability as required and we highly recommend trying out a test area before application to entire area.
Recoatable at the earliest after 12 hours. Protect fresh coating from rain i.e. by using scaffold tarpaulin. Do not use in wet, frosty, or excessively warm weather conditions.
Application is possible with roller, brush or using an airless spraying method. Apply to self contained areas with an absolutely thin coating, with no overlapping and uniformly in one continuous pass as a cross coat.
Upon application, avoid roller edges, ridges, overlapping and over coating coats that have already begun to dry.
What are the colour selection options for Lime Render?
Traditionally, Lime render comes in a naturally occurring off-white colour. However, from a specialist supplier of Limewash – it can be tinted to a range of natural pigment colour options.
Mineral Paints Colour Options:
The mineral paints that we recommend, and can supply, are manufactured by BEECK and include a range of their mineral based products for exteriors’.
Available in more than 300 absolutely non-fading mineral colour tones as produced in the BEECK colour range.
However, Holman Specialist Paints will also be able to tint your exterior paints to match your exact specification from any other colour chart or sample.
Due to the UV resistance of Mineral paint, the colours do not fade and there shouldn’t be a discernible difference between buildings painted in the same colour at different times.
If you would like any further help, advice or guidance on mineral paints, please feel welcome to call us on: 01793 511537 or email: firstname.lastname@example.org
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BEECK Mineral Paints
Mineral Paints Information and Research
History of Mineral Paints
How to Apply Mineral Paints on exterior walls
Masonry Glossary for key term explanation
Sustainability, Ecology and Mineral Paints
Mineral Paints Vs Acrylic Film Forming Coatings
Mineral Paints Vs Lime Render