HomeMy WebLinkAboutLandmarks - Mural on Historic BrickYou never paint unpainted historic masonry. if we had any review authority over the project it
would be denied. It seals the masonry, traps moisture, and results in accelerating of the demise of the
bricks. You simply do not ever paint historic masonry. we would require them to paint a panel and
mount the panel to the building through mortar joints with spacers so it breathes behind. If they have
already painted a primer and it is a latex or non-breathable product they have destroyed the brick. a
mural on historic brick will remove about 30 years from the life of the wall.
Mark T Buechel, AIA
Senior Preservation Architect
State Historic Preservation Office
Wisconsin Historical Society
816 State Street, Madison, Wi. 53706
608-264-6491 (O)
mark.buechel@wisconsinhistory.org
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Older buildings are fairly simple in construction, they usually comprise of thick and solid walls, with no
cavity. The result of this construction method means that moisture will always be, in some form, present
within the building fabric. The original material uses to create these buildings were relatively simple too;
they were softer than the host material (i.e. Stone) and they allowed moisture to escape and not become
trapped. The way I always explain it when I lecture is that for milleniums we always assumed mother
nature would beat us and we allowed for ways for water to get out. Now we think we can conquer mother
nature so we design and build things to be water proof and maintenance free. Neither is possible, mother
nature will eventually always win. With old masonry buildings the soft lime mortar wicks moisture,
moisture transfer is an inherent trait of lime so when water gets into the wall cavity it wicks back
out through the lime mortar. Look at an old building the day after a good rain, the bricks have dried but
the lime mortar is still damp because it is wicking the moisture out from within the wall. Modern mortar
is Portland cement based, Portland cement is a waterproofing material. On a side note this is why we
want pointing to match the historic mortar because if modern hard Portland cement is used it prevents
the moisture within the wall from getting out.
Damp is commonly found in older buildings. Up until recently it was (and unfortunately by some it still is)
believed that the only way to eradicate this issue was to waterproof the entire building with a waterproof
coating such as modern masonry paint or by injecting damp proof courses with the aim to stop water
penetrating the building. Whilst this offered a temporary solution it was and is still not the answer, with
the majority of these applications ultimately failing. Since there is no vapor barrier on the inside the
moisture that moves from inside to out gets stopped at the exterior waterproofing.
Another one of the main reasons for this failure is that a building can undergo significant movement, both
structurally and thermally. Once a crack appears water can penetrate the crack and be held within the
wall behind the non-breathable or waterproof coating, which can include cement and paint. A secondary
issue with cracking is during the winter or colder months, as water freezes it has an expansion rate of
roughly 9% per freeze. As this freeze and thaw cycle is repeated when we reach certain temperatures, the
cracks are able to increase and widen in size, which allows further water to ingress with no means of
escape.
A build-up of moisture can lead to damp within the walls which may cause ‘blistering’ and ‘bubbling’ of
the paint where the water is trying to escape, this is referred to as hydraulic pressure. I’m sure you have
seen this on painted surfaces, the bubbles are from trapped water. In more serious cases the render may
be ‘blown’ or forced off by the pressure of the trapped water. You see this most commonly at parapets
where the front of the brick faces are blown off. This is either because they replaced the roof and ran the
new membrane all the way up the back side of the parapet wall trapping moisture or they painted the
outside. The trapped water is more suspect to freeze when it has weather on both sides like a parapet so
it freezes and blows the faces off the brick.
Water that is trapped within a wall can lead to serious deterioration of the building fabric. Any non-
breathable paint applied to the building will act like a film around its surface. If you imagine wrapping
your walls and ceilings in cling film, this will stop the moisture from going in and out but will trap it and
the water will build up within the surface. This is where the term “film-forming” paint comes from as it
seals the building and stops the building from breathing and allowing moisture out of the walls.
The reason that modern paints such as emulsions and masonry paints are classified as film
forming is due to the chemicals that are used, which create a plastic like layer, enabling them to
sit on the surface of a wall or ceiling.
The most appropriate paint for historic fabric is one that has a low SD Value. There are at least 8 different
ways to measure the breathability of a material. Until the industry adopts a defined standard this will
always be an issue, however when it comes to paint the most accepted and adopted standard is SD Value,
it helps that it is probably the easiest to understand, interpret and compare. SD Value is a German
method, although it used throughout the world, and it stands for steam diffusion or air layer equivalence.
It is a measure of how much of a barrier a paint coating is to water vapor and how easily the vapor can
pass through this barrier, it is measured in meters. The lower the SD Value means that more moisture is
able to pass through, the higher the SD Value, the lower the moisture transfer. Technically any SD below 1
can call itself breathable but a truly breathable paint is one with an SD between 0.01 – 0.5.
Modern paints are not breathable like historic paints were. Historic paints were often a lime wash
paint which is highly breathable. There are some paints that are more breathable than others, clay paints
like tempra are breathable. And you can still buy lime wash paints. Oil can be and it cannot be depending
on the additives. The same with latex, latex is a film that is not breathable but if a minimal amount is in
the paint it hinders but does not destroy it. The historic paint has likely all washed off. If there was still
paint on the wall then painting over it is less likely to cause issues except if you use a non-breathable
paint. If the painted area is small enough the moisture can often still get out by traveling around the
mural. Since moisture flows down I would not let the mural go to the ground, the lower masonry should
not be painted even in a small mural.
Mark T Buechel, AIA
Senior Preservation Architect
State Historic Preservation Office
Wisconsin Historical Society
816 State Street, Madison, Wi. 53706
608-264-6491 (O)
mark.buechel@wisconsinhistory.org
Wisconsin Historical Society
Collecting, Preserving, and Sharing Stories Since 1846
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Sorry for not being able to just say yes or no, unfortunately it is more complex and dependent upon the
overall project with the mural being one piece of that project. I will try to explain below.
From a tax credit perspective everything you do must be reviewed and approved. This includes past
work undertaken by the current owners. However a current owner cannot be held responsible for work
done by a past owner. The program rules technically state everything for as long as you have owned the
property but the reality is they do not hold things against longtime owners who did something a decade
ago that was insensitive. The review precedent NPS set is they will look at all work done in the past five
years with added emphasis on any work done in the past one to three years. So to answer your question,
if they paint a mural now and seek tax credits in the next three years it will be held against them
and could result in overall project denial. This is not guaranteed because what happens is what is
called a cumulative effect review, they will look at all the work being done and how sensitive it is and if it
is a really good project overall they would likely allow the tax credit project to proceed even with the
mural. However if they are proposing questionable treatments in addition to the mural that could result
in overall denial of a tax credit project.
There is no such thing as a perfect project, I’ve had maybe five perfect projects in the nearly 400 I have
done. Most projects in order to succeed require pushing the standards in certain areas. Every project has
a certain political capital they build by the good things they do and they turn around and spend that
capital in getting more questionable treatments approved so overall the project minimally meets the
standards and is approvable. The question owners need to ask themselves is what will I plan for the
future and do I want to start in a hole so to speak requiring spending some of that future capital for the
mural work in an upcoming project? If they do not plan any tax credit projects for at least a few years it
will not be held against them, if they are planning tax credit work in the near future it will be, however as
stated above it will then be dependent upon how good the rest of the project is.
Mark T Buechel, AIA
Senior Preservation Architect
State Historic Preservation Office
Wisconsin Historical Society
816 State Street, Madison, Wi. 53706
608-264-6491 (O)
mark.buechel@wisconsinhistory.org