Catherine Cooper: Hi, my name's Catherine Cooper.
I'm a research scientist at the National Center for Preservation, Technology, and Training.
Today, we're in American Cemetery, and I will be showing you how to take mortar samples
from a masonry structure.
Catherine Cooper: So the reason that we take mortar samples
for analysis is, in order to match recipes when we end up re-pointing a masonry structure.
It's important that the sample that we take answers the question that we're trying to
answer.
So for example, in this wall, we can see that there are areas of relatively significant
loss.
We can also see evidence of a couple of different mortars.
There's this older taupe-colored mortar and then there's a grayish mortar over here.
Catherine Cooper: So if we are going to be re-pointing this
wall, we would want to say, do we want to know what this mortar is over here, which
is a harder Portland cement mixture, or do we want to know what this historic mortar
is?
Catherine Cooper: And in order to do this, I have a couple of
tools that I use, hammer and chisel.
This is a plugging chisel that's actually specifically designed for taking out mortar.
A photo scale, so that when I document what I am removing from the wall, we know what
the scale of that material is, and then it's always important to document what we are sampling,
so a sample bag and marker, so that when you take it back to the lab to do the analysis
yourself or if you send it away, all of the documentation is present.
Catherine Cooper: When choosing what mortar to remove, it's
important to remove it from in context, so I wouldn't want to just pick up a piece of
mortar off the ground.
And to remove it without causing any damage to the brick around it, it's easiest to go
in and remove pieces where there is already loss or weakening.
So, I'm going to take the photo.
Catherine Cooper: In this case, this mortar is not particularly
loose, though I could just break a piece out of the wall, and this is fine.
In case it's a little too hard to do that, you want to use your chisel to direct the
force into the mortar and not in toward the brick.
Essentially, pop the mortar out instead of any possible force cracking the brick.
And this is actually illustrating something else to watch out for when taking a mortar
sample.
Catherine Cooper: This mortar is very soft.
It's got line balls in it, so pretty sure it's going to be a line mortar when we analyze
it, but it also still has its structural integrity so it still has binder and aggregate left
in the sample.
Unlike if I were to just take this powder, I don't know if there's any binder left in
that material, and to analyze just a random powder, that's not going to give us an accurate
recipe for a mix of binder to aggregate.
Catherine Cooper: Regardless of whether you take the material
from the wall using a chisel, or if you can just pop it out with your fingers, the ideal
size for the mortar sample is about 70 to 100 grams worth of material.
This doesn't mean that you need to take a weight or scale measurement in the field.
A sample that's roughly two to three inches long and about half an inch deep would be
sufficient.
And the amount that I'm holding in my hand right now would be plenty for an acid digestion
mortar analysis.
Catherine Cooper: So all of these samples will go in the bag,
and then this can be sent to a laboratory for analysis with the photos of where the
sample was taken, and then also a photo of how the wall looks after you've removed the
mortar from the structure.
Catherine Cooper: Thank you for watching.
If you're interested in any of the other analytical techniques or instruments that we have at
the National Center for preservation, Technology and Training, please look at our website,
and if you have any questions about mortar sampling or mortar analysis, please feel free
to reach out.
Thanks.