This article is part of our series of How To Paint Exterior Renders, including sand and cement render, lime render, and pebble dash.
An Introduction To Lime Render
Lime renders are one of the most traditional type of renders and you can find them on heritage and period buildings. However, this type of render can be also found on modern structures. Lime render is by far the most breathable render product available. Although relatively soft, lime render expands and contracts with the building which makes it particularly suited to older or wooden framed buildings. Traditional lime render can include animal hair or fibres used for reinforcement.
Lime renders apply without the use of corner beads or stop beads. Corner beads and stop beads may sometimes be used in restoration projects to rebuild the substrate but can be hidden underneath the finishing coat. Lime render is often applied in a rustic style following the contours of the building and allowing shading of the finish coat to give a traditional and natural appearance. Lime renders are eco-friendly as they absorb CO2 out of the atmosphere while curing. When fully cured, the lime render sets back to a lime stone like state and provides a very durable finish.
They are also the most breathable type of render allowing moisture to escape. This breathability also means moisture can penetrate into the building fabric. It’s of utmost importance to apply a protective coating in order to protect the building fabric and to prevent damp issues.
Which Paints Are Suitable For Lime Render
When selecting a paint finish for a lime render it is very important to select a paint system that is not only compatible with a lime based substrate but also provides a highly breathable coating. This allows moisture in the walls to evaporate to the outside where it can evaporate into the atmosphere. Otherwise moisture can become trapped behind the paint coating. This can force the moisture to the inside of the property resulting in damp patches.
Our first choice for painting lime render are mineral paint systems such as Mapei or Keim, but preferably lime wash. Silicate based mineral paints are a very traditional paint system which create a strong bond with the substrate. They are primarily made from silica glass with natural pigments and binders. They do not form films like modern paints, instead, once applied a chemical reaction takes place chemically bonding them to lime substrate. This chemical bonding is known as a microcrystalline silicate bond, the paint then effectively become part of the substrate this means they will not peel or flake.
Mineral paints are extremely durable with a high level of breathability whilst remain resistant to the ingress of moisture. Another great benefit of mineral paint on a lime render is the flexibility they provide. As lime renders are soft and flexible they are subject to a degree of movement which could cause modern paints to crack and split. A mineral paint is able to adapt with the substrates natural movement without splitting or cracking. This is particularly important with older buildings that often have very shallow, if any, foundations. An effect of this type of construction can cause the property to move as the ground dries during the Summer and becomes saturated during the Winter months.
Recommendations From Our Technical Team
Mapei Silexcolor Paint System
Silexcolor is an excellent mineral paint from Mapei. The Mapei Silexcolor paint system is a single pack paint formulated from modified potassium-silicate-base combined with selected fillers and pigments. This product is highly breathable and resistant to natural UV light. You can use this paint on both internal and external vertical surfaces. We can colour match this product to most light and pastel RAL colours. It will give substrates a natural looking finish.
KEIM Granital Mineral Paint System
Another option would be Keim’s Graintal system. This paint has high UV, heat and water resistance. Granital is ideal for urban areas due to natural protection against industrial fumes and the potential of acid rain. This system also hinders fungal and algal growth thanks to it’s ideal moisture balance.
The Traditional Paint Company Exterior Limewash
For the traditional approach, Traditional Paint Company’s Exterior Limewash is ideal. Supplied as a paste and utilising lime putty, Lime Wash has been used for the external of Lime Render buildings for over 200 years. This system makes the substrate is less susceptible to store water and is far less likely to erode over time. This paint has different application instructions to standard paint systems. This product is for professional use.