The results of the study are compiled here to respond to the questions proposed by the partners of the study and listed in the scope of study.
Does the source of the lime affect the durability of the limewash? On both the wood and brick samples the limewashes prepared using Graymont hydrated lime and lime putty (washes A, B, D, L, and M) performed better than the limewashes prepared with the high-calcium lime from the Mississippi Lime Company or Virginia Lime Works (washes C, F, I, K, and N). The limewashes prepared with an acrylic-emulsion additive had less notable difference in the performance between lime sources (washes G through I). This result could be due to the powdery surface that was noted in the adhesion tests on both brick and wood samples.
Does the type of lime (e.g., hydrated lime or lime putty) affect the durability of the limewash? The type of lime seemed to have less of an effect on the durability of limewash in the test results of unweathered wood samples. Taking into account the standard deviation of the test results, all wood samples performed in the same range for each recipe. Wash E, with the casein additive and Graymont Niagara lime putty, performed slightly better overall than the other limewashes on wood samples.
The limewashes prepared from putty performed better than those prepared with hydrated lime on the brick samples tested before and after artificial weathering. For the handmade-brick samples the limewashes prepared with putty and applied without a primer performed better than other limewashes.
Does the surface material, or substrate, affect the adhesion or the resistance to abrasion of limewashes? Limewash performed better on brick samples than on either epoxy or wood samples, indicating that the substrate does make a difference. On the wood samples the limewash began flaking off as soon as it dried, indicating poor adhesion, which could have resulted from either the closed-cell matrix or the expansion and contraction of the wood. The limewash on the epoxy samples performed statistically similar to the wood samples of the same washes. Pits created from the filler being loosened during surface sanding of the epoxy may have improved adhesion.
How do various additives and modifications affect the performance of limewashes? Limewashes prepared with salt, alum, molasses, and laundry bluing had the greatest solids deposit and performed well in tests on unweathered samples of all materials. These formulations were also slightly darker in appearance than the other limewashes, which could have been a result of the salt or the molasses individually or the interaction of the two. After weathering, however, these limewashes (washes A through C) performed significantly worse on all materials. This poor performance was markedly noticeable on the brick samples and could have been a result of salt migration through the samples.
The limewashes prepared without additives (washes K, L, M, and N) and applied either with or without a primer performed better than the limewashes prepared with an acrylic or casein additive on brick samples. On brick samples the limewashes prepared without additives or primer (washes L, M, and N) performed best in tests after weathering. The enhanced performance of the limewashes prepared with no additives suggests that these formulations continued to carbonate during artificial weathering. The decrease in performance of limewashes that included additives indicates that the limewashes lost durability during artificial weathering, suggesting that the additives may have affected the limewash matrix or carbonation. On the wood samples the limewashes applied after a primer performed better than those applied without a primer.
Can acrylic-emulsion additives improve or hinder the performance of limewashes? The limewashes prepared with an acrylic-emulsion additive (washes G, H, and I) had a good appearance on all materials. However, they also had the least amount of solids deposited on all samples. In both the adhesion and abrasion tests before and after weathering the limewash had a powdering surface. The powdering and poor test results could indicate disrupted or incomplete carbonation.
How do limewashes behave after longterm exposure to ultraviolet light and temperature? On the wood samples the limewashes deteriorated during artificial weathering. Samples from washes A, F, H, and I were too deteriorated after weathering to continue with the abrasion test. By way of contrast all brick samples showed little visual change from artificial weathering. For almost all samples in washes A through K the colorimetry revealed lightening of the limewashes after artificial weathering. As stated in the discussion of additives, the limewashes prepared without additives and applied without a primer to the handmade brick (washes L, M, and N) performed better after artificial weathering. They were the best performer in tests after artificial weathering. However, limewash prepared with salt additive (washes A, B, and C) experienced a drastic decrease in performance after artificial weathering.
Originally published in APT BULLETIN: JOURNAL OF PRESERVATION TECHNOLOGY / 38:2-3, 2007
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.
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5. Scottish Lime Centre, Technical Advice Note 15: External Lime Coatings on Traditional Buildings (Edinburgh: Historic Scotland, 2001).
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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.