Conclusions

by Sarah Marie Jackson, Tye Botting, and Mary Striegel

The purpose of the study was to test a variety of limewash recipes for possible use on historic brick and wooden structures located in CARI. The immediate goal was to identify lasting, low-cost limewash that could be applied in approximately three layers and would last three to five years. NCPTT partnered with CARI to determine the durability of traditional and modified limewash recipes within certain criteria. In collaboration with the project partners, NCPTT designed a program of testing for limewash on weathered wood, rough-sawn wood, handmade brick, and modern brick.

A variety of limewash recipes was tested on multiple sample materials for possible use at CARI. Based on the results, the most important distinction among the recipes tested was the additives used, rather than the type of lime. The recipes fell into four different categories: salt and molasses additives, casein binder, acrylic binder, and no additives. The adhesion of the limewash was greatly affected by the substrate to which it was applied. The more porous material, brick, allowed for a better adhesion of the limewash, creating a more cohesive coat and increasing durability.

On porous materials such as brick, soluble salts can be very detrimental, contributing to spalling or flaking and micro-fissures in the pore walls, increasing drying times, and changing the porosity of the brick. ¹⁶ Therefore, limewash prepared with a salt additive may be detrimental to porous materials. Such formulations did not perform significantly better than limewash prepared without additives after artificial weathering and actually experienced a significant decrease in performance on both abrasion and adhesion tests after artificial weathering. However, on the handmade brick wash M performed almost twice as well on all tests after artificial weathering. The porous structure of handmade brick makes a primer unnecessary to assist in the adhesion of limewash to the surface. For application on handmade or historic brick wash M (Graymont Niagara lime putty and water) would likely provide the best results in field applications.

None of the limewashes tested were long-lasting on the wood samples, which could be attributed to using only three layers of limewash on the wood samples. The wood itself has been unfinished for numerous years, which most likely contributed to the poor adhesion and would have affected any finish applied to it. However, there was a noticeable difference performance between the washes applied after Edison Coatings Primer #342 and those that were applied to bare wood. The limewashes applied to wood samples after primer performed better during study. In applications where an acrylic primer is deemed an inappropriate treatment on wood, wash E with Graymont Niagara lime putty and casein would likely be a good choice for use. The epoxy samples experienced results that were comparable to the same recipes on the wood samples, indicating they would have a similar durability. Wash E (the Graymont Niagara lime putty, water, molasses, clove oil, and laundry bluing) was the best performer on the wood and epoxy samples.

Future Research Questions

Additional research is needed on the physical and chemical properties of limes available commercially in the United States and Europe in order to gain a clearer understanding of their role in limewash. Application of a greater number of thin coats of the wash, as well as investigation of the effects of temperature and humidity on carbonation, may provide greater insight into the durability of limewash. The use of Pozzalonic additives and the interaction between the minerals in the brick and the limewash should be studied for historical accuracy and possible increased durability. The reversibility of primer and its effect on historic materials should be researched more thoroughly before considering it for use.

Originally published in APT BULLETIN: JOURNAL OF PRESERVATION TECHNOLOGY / 38:2-3, 2007

Notes

1. Laura Soulliere Gates, email to author, Aug. 17, 2006.

2. National Park Service Technical Information Center, 'Class C' Cost Estimating Guide: Historic Preservation and Stabilization (Denver: Denver Service Center, 1993), 18.

3. Colin Mitchell Rose, Traditional Paints, available from http://www.buildingconservation.com/articles/paint/paint.htm.

4. Abbott Lowell Cummings and Richard M. Candee, "Colonial and Federal America: Accounts of Early Painting Practices" in Paint in America: The Colors of Historic Buildings 14 (New York: Wiley, 1994), 14.

5. Scottish Lime Centre, Technical Advice Note 15: External Lime Coatings on Traditional Buildings (Edinburgh: Historic Scotland, 2001).

6. Ibid.

7. John Ashurst and Nicola Ashurst, Mortars, Plasters, and Renders, vol. 3 of English Heritage Technical Handbook (Great Britain: Gower, 1995), 47.

8. Roger W. Moss, "Nineteenth-Century Paints: A Documentary Approach" in Paint in America: The Colors of Historic Buildings (New York: Wiley, 1994), 55.

9. ASTM Subcommittee D01.24, Standard Test Methods for Viscosity by Ford Viscosity Cup, ASTM D 1200-94 (West Conshohocken, Pa.: ASTM, 1996).

10. Marcy Frantom, email to author, Sept. 12, 2005.

11. ASTM Subcommittee D01.23, Standard Test Methods for Abrasion Resistance of Organic Coatings by Falling Abrasive, ASTM D 968-93 (West Conshohocken, Pa.: ASTM, 1996).

12. ASTM Subcommittee D01.23, Standard Test Methods for Measuring Adhesion by Tape Test, ASTM D 3359-95 (West Conshohocken, Pa.: ASTM, 1996).

13. ASTM Subcommittee D01.27, Standard Practice for Conducting Tests on Paint and Related Coatings and Materials Using a Fluorescent UV-Condensation Light- and Water- Exposure Apparatus, ASTM D 4587-91 (West Conshohocken, Pa.: ASTM, 1996).

14. Pete Sotos, conversation with author, Nov. 15, 2006.

15. Ruth Johnston-Feller, Color Science in the Examination of Museum Objects: Nondestructive Procedures (Los Angeles: Getty Conservation Institute, 2001), 35.

16. L. Franke and I. Schumann, "Causes and Mechanisms of Decay of Historic Brick Buildings in Northern Germany," in Conservation of Historic Brick Structures, ed. N. S. Baer, S. Fitz, and R. A. Livingston (Shaftsbury: Donhead, 1998), 26-34.

SARAH MARIE JACKSON joined NCPTT in 2005 as a graduate intern to continue the testing for the limewash study. In 2006 she accepted a permanent position with the Architecture and Engineering Program at NCPTT. She received a master’s degree in historic preservation from the Savannah College of Art and Design.

TYE BOTTING is a research staff member at the Institute for Defense Analyses. He served as the NCPTT/NSU joint faculty researcher for three years. He holds a PhD in nuclear chemistry from Texas A&M University, where he did post-doctoral work in nuclear engineering.

MARY STRIEGEL is responsible for NCPTT’s Materials Research Program, focusing on evaluation of preservation treatments for preventing damage to cultural resources. She also directs investigation of preservation treatments geared towards cemeteries and develops seminars and workshops nationwide. She holds a PhD in inorganic chemistry from Washington University in St. Louis.