A prototype coring tool is used to incrementally extract samples from a salt-affected adobe wall in Mesilla, New Mexico. Permeable lime plaster has been applied to help migrate salts out of load-bearing structure, promoting them to the wall surface as efflorescence.

Salt attack (salt erosion) is an insidious natural process that threatens historic and cultural resources around the world. Driven by capillary action coupled with the evaporation of salt-laden moisture, salt attack is accelerating the loss of historic adobe and other masonry buildings in the arid southwestern United States. Because salts often provide a footprint for moisture movement, understanding and visualizing salt concentrations can yield useful forensic insights into building issues. Precisely locating and measuring concentrated salts allows them to be targeted for removal—setting the clock back for affected structures.

Mesilla Valley Preservation, Inc. (MVP) employed a generous NCPTT grant to design a field toolkit for both collection and accurate measurement of salt loads in the field. The approach provides information and insights that allow preservation specialists to specifically target salts for removal or migration out of load bearing structure—either as a component of conditions assessment, or as part of ongoing maintenance. MVP used the tools to evaluate remediation techniques with permeable sacrificial mud and lime plasters. Print, presentation, and video media were created to communicate and raise awareness of salt attack and its role in damage to masonry structures.

The grant-related work consisted of three principal components:

  • Sample collection kit. The sample collection kit can be used to take incremental core samples of existing adobe (and other masonry) walls. The kit includes a prototype coring tool that mounts in a standard cordless drill. The coring tool allows for sampling at specific intervals in an adobe wall. Samples can also be taken from adjacent soils or when evaluating new materials for salts.
  • Sample processing kit. The sample processing kit uses a precision balance and a calibrated portable off-the-shelf conductivity meter to accurately measure salt loads in adobe samples. The conductivity meter features a sensitive probe that measures the electrical conductivity of a given aqueous solution. A simple methodology and algorithm provide results in terms of a mass ratio.
  • Instructional video series. MVP authored and produced an eight-part video series entitled “Salts of the Earth”, which was published on YouTube and physical media. The video series provides background on the process of salt attack, the operation of the field toolkit, and advice on the use of sacrificial permeable renders through several detailed use cases.

The probe from an Oakton CON 6 meter measures conductivity in an aqueous solution to determine the salt content of adobe samples. Analysis based on the calibrated probe then calculates equivalent salinity in terms of grams of salt per grams of adobe.

MVP has presented its salt attack work at the international EarthUSA conference (EarthUSA 2015: “Remediating Salt Attack in Adobe and Earthen structures”) and other venues.

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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