Trade Advice: How to Apply Limewash
Whether you’ve recently had a request to apply Limewash or are just interested in learning more about this traditional finish, we’re here to help.
In this article, you’ll find some background information on Limewash, plus basic dos and don’ts for working with this finish. Together with our in-depth Product Advice Sheets, we hope this will give you all the information you need when it comes to pricing and allocating time for Limewash projects, as well as achieving a great finish for your customer.
What is Limewash?
Limewash was one of the earliest forms of paint – in fact its formula hasn’t changed all that much in thousands of years, and it’s this that sets it apart from modern paints.
Limewash is not a coating that sits on top of a substrate. Instead, it works by penetrating the substrate and then converting from its liquid state back into limestone. As one of the most water-permeable products on the market, it is very well suited to older properties with solid stone walls.
Advice for applying Limewash
- Before application, make sure you have read the Safety Data Sheet (SDS) and Product Advice Sheet (PAS), which will give more detailed guidance than set out here.
- It is essential that the correct PPE is selected and worn for Limewash application (see PAS).
- Application of Limewash should be undertaken during periods of good weather. It should never be applied in strong winds or under strong direct sunlight. Avoid application if rain is imminent.
- Surfaces must be clean and sound, with all loose or flaking material removed prior to application.
- Apply only one coat of Limewash per day, allowing time for each coat to carbonate (see How does Limewash work? below). Insufficient carbonation time may result in loss of adhesion of the previous coat.
- Lime has a tendency to quickly fall out of suspension from water, so it must be stirred thoroughly both prior to and during application (ideally every 10–15 minutes).
- Prior to application – including the application of subsequent coats – ensure the surface is dampened with clean water.
- Apply with a brush only, working in areas no larger than 1m² at a time.
- Spread Limewash thinly using horizontal, vertical, and diagonal strokes before working the paint in vigorously using a circular motion. If Limewash is applied too thickly this application may result in cracking or crazing.
How does Limewash work?
In simple terms, Limewash is slaked lime (calcium hydroxide) which is suspended in water. Once applied to a suitable surface, the water evaporates and carbon dioxide from our atmosphere combines with the calcium hydroxide to form calcium carbonate, or limestone. This is known as carbonation.
During carbonation, the Limewash bonds to the substrate, develops its colour, and hardens, essentially forming a coloured layer of limestone both on and within the surface.
This process takes time, and we strongly advise that no more than one coat of Limewash should be applied per day. It is equally important that Limewash is not allowed to dry too quickly – drying can be slowed down by shielding the surface with damp hessian.
Some final notes
Coverage of Limewash can be very varied and will be dictated by the nature of the substrate, especially its porosity. As a very rough guide, we would estimate that Limewash could cover 6m2 per litre, per coat.
For significant colour changes using Limewash, Farrow & Ball recommends a minimum of four coats, and up to seven coats may be necessary to fully obliterate the previous colour. Finally, one last reminder to stir Limewash regularly – the last brushful should be as thin as the first!
We hope these few pointers on Limewash will be helpful on your next project. If you’d like any further advice, please visit your nearest Farrow & Ball showroom or give our technical advice line a call on 01202 850240.