This six minute video explains how to prepare and apply limewash.
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Transcript of the video "Application and Preparation of Limewash"
Hello. My name is Sarah Marie Jackson with the National Park Service National Center for Preservation Technology and Training. In this video we will be discussing the application and preparation of lime-wash.
Introduction
Limewash has long been used world-wide as a surface finish on the interior and exterior of buildings, homes, and other structures. Limewash is a mixture of slake lime and water with or without additional additives.
When the mixture dries it reacts with carbon dioxide in the air, called carbonation, to create a tough, rock-like coating. It adheres best to brick, stucco, plaster, adobe and a variety of other porous materials. Wood buildings, fences, and trees were also limewashed historically but the limewash does not adhere as well to this material as it does to porous material.
Lime begins as limestone that is burned at high temperatures. This removes the carbon dioxide and moisture from the stone, creating a calcium oxide which is commonly referred to as quicklime. Quicklime must be slaked with water before it is useable. Slaking refers to the addition of water which leads to an exothermic reaction.
If a small amount of water is added, the result is a dry powder known as hydrated lime. Lime putty is created when a greater amount of water is added to quicklime or hydrated lime.
Documentation
The first step before beginning any project is documentation. It is important to document the structure as you found it before any work begins. This may be done by filling out a survey form or just writing a narrative description of the structure's condition. It is a good idea to take lots of photos before, during, and after completion of the project. Keep in mind to take pictures of both the details and the overall structure.
You should also carefully inspect the structure or surfaces to determine if additional work needs to be done before limewashing. When planning a project sufficient time should be set aside for any drying or setting time needed for all materials. Applying limewash should be the final step in a project.
Preparing Limewash
Limewash was traditionally prepared on site by skilled craftsmen and applied in the spring or fall for optimal temperatures. It is best to apply it when temperatures are between 70 degrees Fahrenheit, give or take 10 degrees. If it is too hot, the limewash will dry too quickly disrupting carbonation and leading to a poor finish.
It is easy to mix a basic limewash with or without additives on site. A high calcium lime is recommended to create a higher quality limewash. Several companies have high calcium hydrated lime and lime putty available for purchase. Remember that lime putty has an endless shelf life as long as it is covered with water and kept in a sealed container.
After deciding on the type of lime you will be using in the limewash you need to mix one part lime for every four parts of water. That will leave you with about 20% lime in your limewash. After mixing well with a whisk or an electric drill with a paint-mixer attachment, check the consistency of the wash. It thin, about the consistency of skim milk.
You can check the consistency using a Zahn cup (or Ford cup) and a dip method. Placing the cup in the limewash begin timing as you pull the cup out of the limewash. We're looking at at a time between 12 and 14 seconds. If it is too thick you can add more water or if the mix is too thin add more lime. After you get it to the right consistency, screen the mix to remove any large or unslaked pieces of lime. An amount large enough to complete the project should be mixed at one time.
It is important to agitate the limewash during application to maintain a consistent mix. I prefer to mix a large amount and pull out smaller amounts to work with as needed. Make sure the limewash is well-mixed before removing the smaller amounts to work with.
Applying Limewash
Next, you're going to want to dampen the building and softly scrub the work surface with a soft-bristle non-metallic brush to remove any dirt, debris, or biological growth. If biological growth is a problem, there are specific cleaners manufactured for use on historic buildings that include a biocide. If you feel that this is needed, be sure to follow the manufacturer's instructions and rinse all cleaners from the surface before beginning the limewash application. Water and a soft-bristle brush will take care of most problems and will not necessitate the additional cost and work of using a chemical cleaner.
When applying limewash you're going to begin by dampening the substrate. The surface should glisten, but have no standing water. I prefer to clean the surface immediately before limewashing so that the material will already be dampened.
After you are done dampening the surface wait a few minutes to make sure the material is no longer drawing water. If the material begins to look dry a few minutes after dampening, the surface is too dry to limewash. It is very important for the surface to be wet enough to allow the limewash to dry slowly. If the limewash dries too quickly the carbonation will be disrupted or make a finish that tends to crack, powder, and lack strength. If time constraints necessitate applying limewash during a time of year when the temperatures are higher than recommended it may be necessary to dampen the surface periodically with a light spray or hang dampened burlap to slow the drying.
Limewash is applied in thin layers, constantly maintaining a wet edge. When I say a wet edge, I am referring to staring in one spot and working out from there not allowing the limewash to dry. There are specifically made brushes for applying limewash called lime brushes that are available from specialty stores or through the Internet. They differ from regular paint brushes in that they are bigger than regular brushes and have stiffer bristles to pick up and distribute the limewash.
Using your lime brush apply the first coat of limewash to a dampened surface. Working the wash into cracks or joints apply the limewash remembering to maintain a wet edge. During application the limewash will remain translucent and become opaque as it dries. It is recommended that you let 24 hours pass between coats to allow the limewash to begin carbonating. To apply successive coats, first dampen the surface then follow the same steps you took when applying the first coat.
Five to eight coats are recommended for the initial application.
More Information
If you are interested in learning more information about limewash, additional resources are available on our web site at http://www.ncptt.nps.gov/ or you can contact Sarah Marie Jackson online or via phone at (318) 356-7444.