Lucy Midelfort measuring salt content of brick samples. Photo by Sheena Simmons, 2017.

Lucy Midelfort measuring salt content of brick samples. Photo by Sheena Simmons, 2017.

 

My name is Lucy Midelfort and I’m originally from Charlottesville, Virginia. I’m a recent graduate of the University of Pennsylvania’s Graduate Program in Historic Preservation with a prior background in environmental science, and now I have come to Natchitoches and NCPTT to research how to mitigate the effects of rapidly changing environmental conditions on salts in masonry. Specifically, I’m going to be testing the performance of a variety of commercial products designed and marketed for prevention of efflorescence in masonry.

While I dive into the design of my testing, I have taken some time to practice how to measure salinity in masonry using a Field Toolkit designed and produced with funding from an NCPTT grant by Mesilla Valley Preservation (MVP) for use with adobe.

Salt damage on brick caused by efflorescence, or crystallization of salts at the surface of the brick. Photo by Jason Church, Bethany Cemetery, 2011.

Salt damage on brick caused by efflorescence, or crystallization of salts at the surface of the brick. Photo by Jason Church, Bethany Cemetery, 2011.

The process involves coring into the masonry at regular intervals and collecting sample that can later be analyzed for salt content. Importantly, the drill bit used to core into the masonry is surrounded by a collection tube (in our case, copper pipe), that ensures that the sample is effectively contained and collected, and vacuuming the coring hole between samples prevents cross-contamination.

Since my research will be centered on treatment for brick, I adapted the toolkit for use with a single brick instead of an adobe wall. Instead of taking samples at 1 inch depth intervals, I took samples every 1/4 inch, and aimed to core through the entire brick’s depth (just under 2 in). Prior to testing, I impregnated my test brick with saltwater, simulating the concentration of typical seawater (35g NaCl/1L H2O). After the water was absorbed by the brick, I artificially dried the brick in an oven to encourage efflorescence and cryptoflorescence of the salt.

The process of coring through the brick resulted in 8 small samples of powdered brick dust, which I stored in individual bags. In order to determine the salinity of each sample, I used MVP’s toolkit to calculate the grams (g) of salt (NaCl) per gram of brick using a digital scale and an off-the-shelf conductivity meter; the higher that ratio, the higher the salinity of the brick at that depth.

A low-fired brick, after being impregnated with salts and dried. Photo by Lucy Midelfort, 2017.

A low-fired brick, after being impregnated with salts and dried. Photo by Lucy Midelfort, 2017.

Samples of brick taken at regular intervals through coring. Photo by Lucy Midelfort, 2017.

Samples of brick taken at regular intervals through coring. Photo by Lucy Midelfort, 2017.

Measuring the conductivity of the solution produced with each brick sample. Photo by Lucy Midelfort, 2017.

Measuring the conductivity of the solution produced with each brick sample. Photo by Lucy Midelfort, 2017.

As expected, I found much higher salt concentrations at both surfaces of the brick than at interior depths. This shows that as masonry dries, salts are carried in solution toward the outer surface of the masonry, at which point the moisture evaporates, leaving the salts to crystallize at or near the surface. It was fun to be able to quantify just how much salt is near the surface, though; as you can see in the chart, the salinity levels near the surface of the brick were exponentially higher than at the center of the brick. It’s great to be able to prove quantitatively what we already know — salts that enter masonry dissolved in ground, rain, or floodwater can end up in extremely high concentrations at the surface of a wall, and can cause great damage there!

Salt content levels found across the depth of the brick, showing exponentially higher levels at each surface.

Salt content levels found across the depth of the brick, showing exponentially higher levels at each surface.

 

National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt[at]nps.gov
Phone: (318) 356-7444
Fax: (318) 356-9119