Laboratory Testing

by Sarah Marie Jackson, Tye Botting, and Mary Striegel

NCPTT tested limewashed samples using artificial weathering and adhesion and abrasion tests that were based on published standard methods. Samples were photographed before and after each test and monitored for color change. A solids test was also performed to determine how much limewash was applied to the samples.

In 2004 the testing began after preparation of samples of handmade brick, modern brick, weathered wood, and rough-sawn new wood provided by CARI. The samples were cored with a drill press using a saw bit with a 1 5⁄8-inch hole so that they would fit in the sample holders. NCPTT later purchased 105 Epoxy Resin, 207 Special Coating Hardener, and 405 Filleting Blend, manufactured by West Systems, the epoxy product used at the historic site. The components were mixed following the instructions supplied by the manufacturer and then cast and cored to the same dimensions as the other materials. The surfaces of the epoxy samples were sanded to remove any remaining chemical residue. Limewash was applied once the samples were prepared.

The limewashes were prepared following instructions shown in Table 1. After the limewash was mixed and screened, the viscosity was determined by dipping a #4 Ford cup into the limewash until overflowing and recording the time for the limewash to run completely through, a process that follows ASTM D 1200-94. ⁹ After checking the viscosity, the samples were dampened and limewash was applied. They were allowed to dry for a minimum of 24 hours before they were redampened and the next coat of limewash was applied.

Quality Finish chose to apply two coats of Edison Coatings Primer #342 to consolidate brick surfaces and assist in adhesion to wood samples for washes A through K. ¹⁰ Washes A through I were applied to the handmade brick, modern brick, weathered wood, and rough-sawn new wood. Wash K was applied to the handmade and modern brick. An NCPTT intern applied the primer and the best performers from the wood test — washes D, E, and G — to the epoxy following the same instructions used with the wood. NCPTT staff applied washes L, M, and N to the handmade brick and weathered wood without a primer.

The tests were performed in triplicate for each limewash on each sample material. The samples were photographed before and after each test to maintain a visual record throughout the study. A Minolta colorimeter was used to record color data for all samples using the CIE standard; results from before and after the weathering, adhesion, and abrasion tests were compared for color changes.

The solids test followed a simple gravimetric method to determine the total mass of the limewash applied to the samples. Masses were taken of the samples before limewash was applied and after the final coat had dried. The mass differences before initial and after final application were averaged for each sample, giving the amount of solids deposited. Depending on the limewash applied, the solids deposit would be either lime or a mixture of lime and additives, such as the salt additive in washes A, B, and C.

Abrasion testing, based on ASTM D 968-93, was used to rank how a limewash might stand up over time when subjected to abrasion from wind- and rain-borne particles.11 The testing apparatus was a funnel fitted over a guide tube and supported vertically. The samples were mounted in a holder positioned 45 degrees from vertical exactly 1 inch below the outlet tube. Sand was loaded into the funnel in 1-liter increments and discharged over the sample until the limewash began to wear away and the substrate was visible. As the substrate became visible, the amount of sand was decreased to 250-milliliter increments until a patch 4 millimeters in diameter was exposed. The amount of sand needed to remove the limewash was recorded. The test was performed on three samples from each wash for each sample material and the results averaged. The best performers were those samples that required the highest amount of sand, indicating that they had formed a harder, more cohesive finish.

Adhesion testing evaluated how firmly the limewash bonded to the samples, following ASTM D 3359-95. An X cut was made with a sharp blade through the limewash to the substrate using a template with the smallest angle of the intersection between 30 and 45 degrees. Pressure-sensitive tape was applied over the cut and smoothed down with a rubber eraser, and the tape was removed in a quick, non-jerking motion. Each limewash was rated on a scale of 5A (best) to 0A (worst), and the results were averaged. ¹² The best performers were the samples with the least limewash loss, indicating the limewashes that bonded most tightly to the material.

Artificial weathering was performed on samples using a Q-Lab QUV Weathering Tester following a procedure based on ASTM D 4587-91. The controlled conditions of this test cannot correlate directly to outdoor exposure but do give an idea of how the limewashes might weather comparatively over time. The samples were mounted in holders with silicone adhesive and placed in the QUV. They were subjected to four hours of ultraviolet light at 140°F (60°C), followed by four hours of condensation and dark at 122°F (50°C) for 100 cycles, for a total of 800 hours of exposure. ¹³ The sample locations within the weatherometer were rotated daily to ensure even exposure and eliminate any instrumental irregularities. Artificially weathered samples were rated on a scale of 5A (best) to 0A (worst), similar to that used in the adhesion-rating system. The samples were evaluated visually based on the overall appearance and the amount of limewash remaining on the samples. The results from each limewash were averaged to determine the best performers. Mass differences are commonly used to determine loss from weathering, but the final masses of this test were affected by the silicone that had been used to mount the samples and adhered to the edges of the samples after testing.

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.