Hello, my name is Sarah Marie Jackson with the National Park Service National Center
for Preservation Technology and Training and in this video we'll be discussing application and
preparation of lime wash. Lime wash has long been used worldwide as a surface finish on the
interior and exterior of homes buildings and other structures. Lime wash is a mixture of slate, 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 curry. It adheres fast to brick
stucco plaster Adobe and a variety of other porous materials. Wood building fences and
trees were also lime washed historically but the lime wash 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 stone creating calcium oxide which is
commonly referred to a quick lime. Quick lime 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 quick lime or hydrated lime. The first step before beginning any
project is documentation. It is important to document the structure as you found it before
and work begins. This may be done by filling out a survey form or just writing a narrative
description of the structures condition. It is a good idea to take lots of photos before during and
after the completion of the project. Keep in mind to take pictures of both the details and
the overall structure. You should also carefully inspect a structure or surface to determine that
additional work does not need to be done before lime washing. When planning a project sufficient
time should be set aside for any drawing or setting time needed for all materials. Applying
lime wash to be the final step in a project. Lime wash was traditionally prepared on-site
by skilled craftsmen and applied in the spring or the fall for optimal temperatures. It is a best to
apply it when temperatures are around 70 degrees Fahrenheit give or take 10 degrees. If it is too
hot the line wash will dry too quickly disrupting carbonation and leading to a poor finish.
It is easy to mix a basic lime wash with or without additives on-site and high calcium lime is
recommended to create a higher quality lime wash. 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's covered with water and kept in a sealed container after deciding on the type of lime you
will be using in the lime wash you need to mix one part lime for every four parts of water that
will leave you with about 20 percent lime in your lime wash. After mixing it well with a whisk or
an electric drill with a paint mixer attachment check the consistency of the wash. It should be
thin about the consistency of skim milk. You can check the consistency using a yawn or four cup and
a tip method placing the cup in the lime wash to begin timing as you pull the cup out of the lime
wash. We are looking 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 unsafe uses of lime an amount large enough to complete the project
should be mixed at one time it is important to agitate the lime wash during applications 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 lime wash is well mixed before removing the smaller amounts to
work with. Next you're going to want to dampen the building and softly scrub your work surface with
a soft bristle nonmetallic 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 biozide. 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 lime wash 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 lime wash you are going to begin by dampening
the substrate. The surface should glisten but have no standing water. I prefer to clean the
surface immediately before lime wash so the material will already be dampened. After
you're 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 for lime wash. It is very important that the substrate be damp enough to allow the lime wash to
dry slowly if the lime wash dries too quickly the carbonation will be disrupted or meaning finished
that tends to crack powder and lacks strength if time constraints necessitate applying lime
wash during a time of year when the temperatures are higher than recommended maybe necessary to
dampen the surface periodically with a light spray or hanging dampened burlap to slow the
dry. Lime washes applied in thin layers costly maintaining a wet edge when I say a wet edge I
am referring to starting in one spot and working out from there not allowing the lime wash to dry.
There are specifically main brushes for a fine line wash called line 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 brissles to pick up and distribute the
lime wash. Using your line brush apply the first coat of lime wash to a dampened surface working
the wash into cracks or joints apply the lime wash remembering to maintain a wet edge during
application the lime wash will be translucent and become opaque as it dries. It is recommended that
you let 24 hours pass between coats to allow the lime wash to begin carbonate to apply successive
coats first dampen the surface and follow the same steps you took when applying the first coat. Five
to eight coats are recommended for the initial application if you're interested in learning more
information about lime wash additional resources are available on our website at www.ncptt.nps.gov