Limewash is a simple traditional paint based on lime and water which has been used to decorate homes for centuries.
In spite of the simple formulation, there are differences in the types of lime which can be used when making this paint. You’ll see reference to Lime putty, hydrated lime, and hydraulic lime. They’re all slightly different materials used to create this traditional finish.
This guide gives an overview of what a traditional limewash contains, and what the different ingredients are, and how they can be used. We’ll also take a look at modern alternatives, and how they compare.
What is Limewash Made From?
The most basic recipe contains just lime and water, or more accurately slaked lime (Calcium Hydroxide) in water.
The basic ingredients are just:-
- Slaked lime, traditionally in the form of lime putty.
- Water
- Pigment, if a coloured limewash is required.
Other ingredients have sometimes been added to historic limewash recipes to alter characteristics such as adhesion or weather resistance, but lime and water form the basis of the paint.
The lime itself acts as both the body of the paint and its binder. As limewash cures, calcium hydroxide reacts with carbon dioxide in the air and gradually reforms calcium carbonate.
See also: What is limewash paint?
What Type of Lime is Used to Make Limewash?
Limewash is usually made by thinning lime putty with water to create a very runny paint. It can also be made from other forms of lime, including hydrated lime or sometimes hydraulic lime.
The names are similar, but these are distinct materials with different properties.
Lime Putty Vs Hydrated Lime Vs Hydraulic Lime: What's the Difference?
These lime products have similar names, but the materials are produced differently and also behave differently during use.
Lime putty - Made by slaking quicklime with water creating a wet paste of Calcium Hydroxide. It’s non hydraulic, meaning it hardens through a reaction with Carbon Dioxide in the air through a process called carbonation. Lime putty is highly vapour permeable and breathable. It allows older solid wall buildings to manage movement and lets moisture escape.
Hydrated lime - Also a type of slaked lime, but supplied as a dry powder rather than a wet putty. It can be mixed with water to make a putty like material or limewash, but doesn’t develop quite the same flexibility and binding qualities as a traditionally made putty that’s been matured wet.
Hydraulic lime - Contains reactive minerals that allow it to set in the presence of water, rather than relying solely on air exposure to harden. It’s commonly used for mortars, renders, and other building work where a faster set or greater early strength and weather resistance are needed. Different grades are chosen to suit the masonry type and level of exposure to weather.
The similarity of the terminology can cause confusion - hydrated and hydraulic don’t mean the same thing. For traditional non hydraulic limewash, mature lime putty is the most commonly used material.
Making Limewash From Lime Putty
Making limewash from lime putty involves diluting putty with clean water and mixing it thoroughly to achieve the right paint consistence.
Recommendations around putty to water ratios vary depending on the properties of the lime putty you decide to use. A common ratio is 1 part lime putty to 1-2 parts water, or a 1:1 mixture.
The consistency of the finished limewash will vary, Specialist lime product supplier Ty Mawr recommends an end consistency somewhere between milk and single cream in their lime putty information sheet.
If colour is required, a suitable lime fast colour pigment can also be added.
The Mixing Process
Mixing putty and water to make limewash is relatively straightforward. Just mix the putty and water thoroughly using a hand whisk or paint mixing paddle until the limewash is smooth and lump free.
You’ll need to ensure you stir your mix frequently during application. Limewash is a suspension, so heavier lime particles will settle to the bottom if left standing.
Can You Make Limewash With Hydrated Lime?
It’s possible to make limewash from hydrated lime, also called bag lime, as an alternative to putty, however recommendations around using it vary.
Conservation specialists such as SPAB generally favour using mature lime putty because it has better plasticity and binding qualities. Their limewash guidance says “The alternative of preparing putty from ordinary (non-hydraulic) bagged lime can result in inferior limewash.”
Where hydrated lime is used, it's generally recommended it should be as fresh as possible because it starts to degrade as soon as it’s made. Ty Mawr’s types of lime guidance recommends that if it is the only option, it should be left to soak for two days in clean water. Interestingly, they also advise it should not be used in pre-1919 buildings.
A basic process to use hydrated lime for limewash is:
- Use fresh non hydraulic hydrated lime.
- Mix thoroughly with clean water to form a wet putty
- Allow the mixture to soak for 2 days before mixing again.
- Add further water until it reaches a thin, milk like consistency.
- Add lime fast colour pigment if required.
Methods do vary around the use of this material to make limewash, so do get proper expert advice about the substrate you’re intending to finish.
Can You Make Lime Putty From Hydrated Lime?
Yes. Hydrated lime powder can be soaked in water to create a form of lime putty. It’s still calcium hydroxide, but its physical characteristics will differ.
Why Does Limewash Work as a Paint?
Limewash works differently to conventional paint. When applied to mineral substrates, the wash is drawn into tiny pores and surface irregularities. As it carbonates, it hardens in place, creating a finish that is bonded into the wall rather than just coating it.
As the finish carbonates, the calcium hydroxide in the wet limewash absorbs carbon dioxide from the air and gradually turns back into calcium carbonate - returning to the mineral form that lime started from.
Why is Limewash Breathable?
Limewash is a highly breathable or vapour permeable paint. The finished coating allows water vapour to move through the walls and paint layer, evaporating harmlessly away rather than being trapped inside the walls and causing damage.
This function is particularly important in buildings with a traditional solid wall construction.
See also:
What Else Can be Added to Limewash?
Because lime itself acts as a binder, traditional limewash doesn’t need a complex list of ingredients. Pigments and other materials can be added to change its colour or alter how the finished coating performs.
Adding Pigments to Limewash
Limewash is usually white, but earth and mineral pigments can be used to create a coloured limewash finish.
Lime is strongly alkaline, which means any pigments added need to be alkali resistant (lime fast). It’s difficult to achieve strong colours when adding pigments to limewash, as the base colour is a strong white and there are limits on how much pigment can be added to the mix.
Traditional Limewash Additives
Historic limewash recipes can include ingredients like casein, tallow, or linseed oil. They were generally used to change properties like adhesion, water resistance, or durability.
They weren’t essential ingredients, and using these types of traditional additives can involve trade offs. For example, oils and fats will make a coating more water resistant at the cost of vapour permeability.
If you feel you want a traditional lime finish with additional durability or ease of application - you might wish to consider a modern lime based paint.
Traditional Limewash vs Modern Lime Paint
Limewash is a very simple coating made from lime and water. Modern lime paints use the same mineral principles but have added other modern formulations using natural ingredients, making them excellent limewash alternatives. This creates a more durable and easy to apply paint, without compromising the breathability and mineral formulation.
For example:-
- Auro 344 contains water and calcium hydroxide alongside titanium dioxide, mineral fillers and cellulose. Compared with traditional site mixed limewash it creates a more consisted ready to use paint with predictable coverage, easier application, and high breathability.
- Graphenstone Siena - uses aerated lime as its base combined with Graphenstone’s Graphene technology and pigment. It creates a ready to use lime paint with more consistent colour, high breathability, and improved resistance, durability, and washability.
Is Traditional Limewash the Best Choice for Interior Walls?
Not necessarily. Traditional limewash can be an excellent choice as a paint for lime plaster and other porous mineral surfaces, particularly where an authentic finish is wanted.
Where the priority is breathability rather than traditional limewash itself, a formulated lime or mineral paint may offer a more practical alternative.
Need help deciding if limewash or a more modern alternative is the best choice for your project? Contact us, and one of our team of paint experts will be delighted to help.
