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Introduction
This report is an executive summary of testing undertaken by NCPTT in partnership with the Cane River Creole National Historical Park (CARI) and Quality Finish.
In December 2003 meetings were held to discuss applying limewash to the brick cabins at Magnolia Plantation in hopes of prolonging the life of the structures. We developed a study to determine the durability of traditional and modified limewash recipes within certain criteria. CARI wanted to identify a durable low cost limewash that was applied in approximately three coats. As the project progressed we decided to also test limewash on wood, since CARI expressed interest in applying limewash to the wood structures at Oakland plantation. 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.
Quality Finish researched possible limewash recipes that may have been used locally by interviewing community members. They were not able to identify recipes used in the community and thus turned to published limewash recipes, including a limewash identified through NPS contracting schedules. We worked together to prepare wood and brick test samples. Starting in November 2004, Quality Finish applied ten separate washes on handmade and modern brick samples. On all brick samples, an Edison acrylic emulsion was used as a primer. The same limewash recipes were applied to weather and rough-sawn wood, except for the wash K, the Virginia Limeworks putty and water which was only applied to the brick samples.
As of October 2005, NCPTT has completed scheduled testing on all samples. However the Center has decided to undertake additional testing, including traditional limewashes of lime and water on brick and wood samples without an Edison primer and the three best performing limewashes from the wood test on epoxy samples. The results from the additional testing are expected by the beginning of 2006. This report will focus on the results of durability testing of limewash recipes on the original handmade and modern brick samples.
Testing Methods
NCPTT tested limewashed handmade and modern brick samples using artificial weathering, adhesion, and abrasion testing according to ASTM standard methods. We photographed samples before and after each test and monitored them for color change with a Minolta colorimeter. To perform artificial weathering, we placed the samples in a QUV weatherometer and subjected them to four hours of UV light exposure and four hours of condensation in the dark continuously alternating for 800 hours. This accelerated weathering gives us an idea of how the limewash may age over time. For the adhesion test, we cut an “X” through the limewash to the sample, and then placed pressure sensitive tape over the cut. Upon removal of the tape, we assessed how much limewash was removed. This test evaluates how firmly the limewash bonds to the samples. In the abrasion test, we placed samples in a holder and poured measured amounts of falling sand on to the surface to determine how much sand is needed to remove a 4 mm (.1575 inch) diameter circular area of limewash. The abrasion test allows us to rank how a limewash will stand up to abrasion from windand rain-borne particles and from people touching the buildings. With the help of Quality Finish, we also performed a solids test to determine how much limewash is being applied to the samples.
Test Results: Handmade Bricks
We evaluated limewashed brick samples before and after artificial weathering using visual appearance, abrasion testing and adhesion testing. Test results are represented as an average of the results from the individual samples for each wash. Three replicates were prepared for each wash. Individual results for each sample are recorded in the appendix that is included with the report. A ranking system was devised in order to evaluate the results of each test. Based on their performance, we ranked each limewash from best to worst for relative change in appearance, adhesion, and abrasion for samples both before and after weathering. Those with the best performance ranked a 10 and those with the worst performance ranked a 1. The rankings were then totaled for each wash, creating an overall ranking.
For unweathered samples, washes F, H, and D performed the best in adhesion testing. This means that washes F, H, and D bound most tightly to the brick prior to weathering. Upon abrasion testing, unweathered samples of washes A, B, and K performed the best. This means that they formed a harder coating that was more cohesive.
After artificial weathering, each wash was visually evaluated and we found that washes A, E, and K performed the best, although all of the washes performed very well. Washes C, E, and G performed the best in the adhesion test of the artificially weathered samples with no variability in any of the results. Wash K also averaged the same rating as the best performers, but there was a large standard deviation. Washes A, B, and D performed best in the abrasion test on the weathered samples although washes A and B performed almost twice as well as wash D.
For the handmade brick the three best performing limewashes were washes A, E, and K. Limewash A is Graymont’s Ivory hydrated lime, table salt, alum, unsulphured molasses, laundry bluing, and water. Wash A performed the best in the abrasion test both for the unweathered and artificially weathered samples. For the abrasion test of the samples that were not weathered wash A averaged 93 liters, almost two times greater than the next best performing wash B and three times greater than the third best performing wash K. For the abrasion test on the samples that were weathered wash A also performed the best with an average of 8.25 liters that had a small standard deviation. For the adhesion test on samples that were not artificially weathered it performed in the middle of the group and towards the bottom of the group for samples that were artificially weathered.
The second best performers on the handmade brick were washes E and K. Wash E is Graymont’s Niagara lime putty, unsulphered molasses, laundry bluing, clove oil, and water. It performed equally with A and K as the best that were artificially weathered and equally with C and G as the best in the adhesion test on the samples that were artificially weathered. In the abrasion test on the samples that were artificially weathered wash E performed in the middle group. For the samples that were not weathered wash E rated as the fourth best in the adhesion test and as the third worst in the abrasion test.
Wash K performed equally as well as wash E. Wash K is the Virginia Limeworks lime putty and water. For the artificial weathering wash K was grouped in the best rating with washes A and E. For the rest of the tests it ranked in the middle group when compared with the other washes. Wash K is still considered a good performer despite it ranking in the middle of the group in several tests where a few washes far exceeded the others in performance such as the artificial weathering.
Test Results: Modern Brick
For unweathered samples, washes K, F, and D performed the best in adhesion testing. This means that washes K, F, and D bound most tightly to the wood prior to weathering. Upon abrasion testing, unweathered samples of washes A, B, and C performed the best. This means that they formed a harder coating that was more cohesive.
After artificial weathering, each wash was visually evaluated and we found that washes D, H, and K performed the best, although all of the washes performed very well. Also, we found that washes I, H, and F were the best performers in the adhesion tests after weathering. Washes B, E, and A performed the best in abrasion tests on the weathered limewashed samples, although wash B performed twice as well as washes A and E.
For the modern brick samples we found that wash B performed the best overall of all the washes. Wash B is Graymont’s Niagara lime putty, salt, alum, unsulphured molasses, laundry bluing, and water. It performed well on the adhesion, abrasion, artificial weathering, and abrasion test after artificial weathering. In the abrasion test on the samples that were not artificially weathered it performed better than all but wash A. On the adhesion test after weathering it performed poorly.
We found the second best performing limewash on modern brick to be Wash D. Wash D performed well on the adhesion test and the artificial weathering. It performed poorly on the abrasion test before and after weathering and the adhesion test after weathering.
The third best performing limewashes on the modern brick were washes A and K that performed equally well. Wash A performed the best on the abrasion test requiring three times as many liters of sand as the test’s second best performer wash B. Wash A performed poorly on the adhesion test before weathering and the adhesion and abrasion tests after weathering. In the artificial weathering wash K ranked third from last, but all of the washes performed well and the differences were very slight. Wash K performed well in the adhesion and artificial weathering test, but poorly in the adhesion and abrasion test after weathering. On the abrasion test it performed in the middle of the group.
Recommendations
Any recommendation for field application based on the results of this data must take into account the dynamic of moisture migration in masonry walls and processes such as efflorescence and subflorescence that may affect the choice of the ideal coating. Efflorescence is when salt appears on the surface of materials and subflorescence is when salt crystallizes beneath the surface of a material. Subflorescence is created when soluble salts in a liquid travel through a brick until temperature and atmospheric pressures cause the liquid to evaporate leaving behind the salt crystal deposits in the interior voids of a brick.1 Soluble salts can be very detrimental to bricks contributing to physical problems such as spalling or flaking, increasing dry times, changing porosity, and micro fissures in the pore walls.2 Soluble salts can transfer naturally through rising damp, pollution in the atmosphere,3 mortar used to set the bricks, adjacent materials, or be present from the clay used in the brick construction.4 We would recommend not introducing more salt to brick structures by using a limewash recipe that contains salt. During the artificial weathering process the modern brick samples with washes A, B, and C all experienced significant efflorescence on the side opposite of the limewash. We did not note any efflorescence on the historic brick, but that could have been affected by several factors such as porosity.
Although Wash A performed the best on the handmade brick and Wash B performed the best on the modern brick we feel that using a recipe with a salt additive could be detrimental to the bricks. Wash K performed well on both handmade brick and modern brick and is our recommendation for use on the brick structures at Cane River Creole National Historical Park. Wash K consists of Virginia Lime Putty and water and has no additives that could be detrimental to the brick.
Alternative limewashes include washes D and E. Wash E performed well on the handmade brick and is in the group of top performers, but on the modern brick it performed in the middle of the group. Wash D rated as the second best performer on the modern brick, but on the handmade brick it falls in the middle of the group.
It should be noted that all samples were subjected to color analysis before and after artificial aging. All limewashes display some color change over time and tend to darken and yellow. Since all washes changed approximately the same, we did not include these tests in our recommendations.
1 Weaver, Martin E. with F.G. Matero, Conserving Buildings: guide to techniques and materials (New York, John Wiley & Sons, 1993), 120.
2 Franke, L. and I. Schumann, “Causes and Mechanisms of Decay of Historic Brick Buildings in Northern Germany,” in Conservation of Historic Brick Structures, eds. N.S. Baer, S. Fitz, and R.A. Livingston (Shaftsbury: Donhead, 1998), 26- 34.
3 Caner-Saltik, E.N., I. Schumann, and L. Franke, “Stages of Damage in the Structure of Brick Due to Salt Crystallization,” in Conservation of Historic Brick Structures, eds. N.S. Baer, S. Fitz, and R.A. Livingston (Shaftsbury: Donhead, 1998), 49.
4 Ashurst, John and Nicola, Practical building conservation: English Heritage technical handbook, vol. 2 Brick, Terracotta, and Earth (Aldershot, Gower, 1995), 50.
Limewash Recipes
| Wash | Lime | Part A | Part B | Mix | ||||
|---|---|---|---|---|---|---|---|---|
| Wash A | Graymont Ivory hydrated lime | 1lb. Table salt, .5 oz alum, 1/3 cup unsulphured molasses, 1/12 tsp laundry bluing. Mix in 2 1/2 cups hot water. | 4 1/4 cups hydrated lime mixed with 4 1/2 cups hot water let stand 12 hours | Mix parts A & B in equal parts. Viscosity 17 seconds at 70 degrees in #4 Ford cup. | ||||
| Wash B | Graymont Niagara lime putty | 1lb. Table salt, .5 oz alum, 1/3 cup unsulphured molasses, 1/12 tsp laundry bluing. Mix in 3 cups hot water. | Mix 8 1/2 cups Niagara putty with 4 cups hot water. Let stand 12 hours. | Mix parts A & B in equal parts. Viscosity 17 seconds at 70 degrees in #4 Ford cup. | ||||
| Wash C | Virginia Limeworks lime putty | 1lb. Table salt, .5 oz alum, 1/3 cup unsulphured molasses, 1/12 tsp laundry bluing. Mix in 2 1/2 cups hot water. | Mix 8 1/2 cups Virginia Limeworks with 4.75 cups hot water. | Mix parts A & B in equal parts. Viscosity 17 seconds at 70 degrees in #4 Ford cup. | ||||
| Wash D | Graymont Ivory hydrated lime | 1/3 cup unsulphered molasses, 1/12 tsp laundry bluing, 1/4 tsp clove oil. Mix with 1.5 cups hot water. | 4 1/4 cups hydrated lime mixed with 2 1/2 cups hot water. Let stand 12 hours. | Mix together A & B. Viscosity same as A. Add 4 tsp. Schmincke Casein Binding Medium per 1 cup limewash. | ||||
| Wash E | Graymont Niagara lime putty | 1/3 cup unsulphered molasses, 1/12 tsp laundry bluing, 1/4 tsp clove oil. Mix with 2 1/2 cups hot water. | 8 1/2 cups putty with 2 1/4 cups hot water. Let stand 12 hours. | Mix together A & B. Viscosity same as A. Add 4 tsp. Schmincke Casein Binding Medium per 1 cup limewash. | ||||
| Wash F | Virginia Limeworks lime putty | 1/3 cup unsulphered molasses, 1/12 tsp laundry bluing, 1/4 tsp clove oil. Mix with 1 1/2 cups hot water. | 8 1/2 cups Virginia Limeworks putty mixed with 2 1/4 cups hot water. Let stand 12 hours. | Mix together A & B. Viscosity same as A. Add 4 tsp. Schmincke Casein Binding Medium per 1 cup limewash. | ||||
| Wash G | Graymont Ivory hydrated lime | 4 1/4 cups hydrated lime mixed with 7 1/2 cups hot water. Let stand 12 hours. | Check viscosity 17 seconds at 70 degrees. For each 1 cup of limewash, add 2 tablespoons of Edison. | |||||
| Wash H | Graymont Niagara lime putty | 8 1/2 cups Niagara lime putty mixed with 5 cups hot water. Let stand 12 hours. | Check viscosity 17 seconds at 70 degrees. For each 1 cup of limewash, add 2 tablespoons of Edison. | |||||
| Wash I | Virginia Limeworks lime putty | 8 1/2 cups Virginia lime putty with 5 cups hot water. Let stand 12 hours. | Check viscosity 17 seconds at 70 degrees. For each 1 cup of limewash, add 2 tablespoons of Edison. | |||||
| Wash K | Virginia Limeworks lime putty | 8 1/2 cups Virginia lime putty with 5 cups hot water. Let stand 12 hours | Check viscosity 17 seconds at 70 degrees in #4 Ford cup. | |||||
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Recipies provided by Quality Finish.
Limewash Recipes Matrix
Limewash Recipes Matrix 1
Limewash Recipes Matrix 2
Limewash Recipes Matrix 3
Limewash Recipes Matrix 4
QUV Artificial Weathering
Artificial weathering was selected as one of the steps in the study to decrease the amount of time required to age the samples while imparting changes due to weathering.
Weathering Cycle
The weathering cycle selected for the study is 4 hours of UV light exposure at 60 degrees Celsius (~120 degrees Fahrenheit), followed by 4 hours of condensation in the dark at 50 degrees Celsius (~140 degrees Fahrenheit). This cycle will be repeated for a period of 800 hours. Calibrating the irradiance and temperature of the QUV prior to performing the experiment is important to ensure accurate and repeatable test results.
Limewash Experiment: QUV Rating
Adhesion by Tape Test
Limewash Experiment: Adhesion Rating
Abrasion by Falling Sand
Abrasion Testing Procedure
- Assemble the apparatus so that the sample holder is directly in-line with the sand tube and funnel, and so that the large collection bin is able to trap all used sand.
- Choose sample to abrade and mount it in holder directly under the outlet tube, so that the center of the flow will hit the center of the sample.
- Position the sample so that the nearest portion of it to the end of the outlet tube is exactly one (1) inch from the outlet tube.
- Fill the one liter beaker with sand to exactly the 1000 mL mark.
- Load the upper funnel with the sand, thus allowing sand to abrade the sample.
- Record each 1L of sand used.
- Repeat steps 4 through 6 until the sample begins to show substrate, but empty the collection bin of its sand before the sand “backs up” onto the sample.
- Once substrate begins to show, switch to using 250 mL at a time by using the plastic beaker.
- Make sure to record exactly the total volume of sand used.
- The run is complete once a patch of substrate is exposed that measures 4mm in diameter (no more, no less). Use the longest diameter if the patch is not circular.
- The final piece of data for each sample is then the volume of sand required to expose a 4mm diameter patch of substrate.
Results: Solids Test
Experimental Matrix: Handmade Brick 1
Experimental Matrix: Handmade Brick 2
Experimental Matrix: Handmade Brick 3
Experimental Matrix: Handmade Brick 4
Measuring Adhesion by Tape Test
Adhesion Test: Handmade Brick 1
Adhesion Test: Handmade Brick 2
Adhesion Test: Modern Brick 1
Adhesion Test: Modern Brick 2
Abrasion Test
Abrasion Test: Handmade Brick 1
Abrasion Test: Handmade Brick 2
Abrasion Test: Modern Brick 1
Abrasion Test: Modern Brick 1
QUV Samples
QUV Samples: Handmade Brick 1
QUV Samples: Handmade Brick 2
QUV Samples: Modern Brick 1
QUV Samples: Modern Brick 2
Colorimetry
Colorimetry Handmade Brick 1
Colorimetry Handmade Brick 2
Colorimetry Handmade Brick 3
Colorimetry Handmade Brick 4
Colorimetry Handmade Brick 5
Colorimetry Handmade Brick 6
Colorimetry Modern Brick 1
Colorimetry Modern Brick 2
Colorimetry Modern Brick 3
Colorimetry Modern Brick 4
Colorimetry Modern Brick 5
Colorimetry Modern Brick 6
Solids Test
Solids Test: Handmade Brick 1
Solids Test: Handmade Brick 2
Solids Test: Handmade Brick 3
Solids Test: Handmade Brick 4
Solids Test: Modern Brick 1
Solids Test: Modern Brick 2
Solids Test: Modern Brick 3
Solids Test: Modern Brick 4
Measuring Adhesion by Tape Test
Adhesion Test: Manmade Brick 1
Adhesion Test: Handmade Brick 2
Adhesion Test: Modern Brick 1
Adhesion Test: Modern Brick 2
Abrasion Test
Abrasion Test: Handmade Brick 1
Abrasion Test: Handmade Brick 2
Abrasion Test: Modern Brick 1
Abrasion Test: Modern Brick 2
Overall Rating
Overall Rating
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