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.