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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.
Limewash has long been used world-wide as a surface
finish on the interior and exterior of homes,
buildings, 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.
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.
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.
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.
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.
If you are interested in learning more information
about limewash, additional resources are available
on our web site at www.ncptt.nps.gov