Award-winning NCPTT Research takes another look at historic building protectant
Its most popular cultural reference may come out of The Adventures of Tom Sawyer, but limewash (also known as whitewash) is enjoying renewed interest as a protectant for historic structures, thanks in part to research undertaken by NCPTT and its partners.
Limewash has been used as a surface finish for centuries worldwide. It was widely used in the United States from the 19th to mid-20th centuries to protect structures (and fences, of course) against pests and weathering.
Seeking traditionally appropriate ways to protect their plantation buildings, staff at Cane River Creole National Historical Park (CARI) kept coming back to limewash as their solution of choice.
“Historically most of the buildings at this park were coated with limewash, and that material served multiple purposes in much the same way as the finish coating on adobe in the Southwest,” Laura Gates, CARI superintendent, said. “It provided a layer of protection from the onslaught of wind and water that weathered buildings’ exteriors.”
Limewash can be made with just slaked lime and water. But over the years, tradesmen created their own recipes using a variety of additives. The use of limewash faded to nonexistence with the advent of modern paints, improved contruction materials and streamlined labor practices over the latter half of the 20th century.
Unable to find modern research on which of the many traditional recipes would best protect the buildings, CARI turned to NCPTT. The two organizations partnered with Quality Finish Painters to conduct the study. Researchers used finish remnants to confirm the use of limewash on the wood and brick surfaces at the park and followed up with research to determine appropriate recipes.
While Quality Finish researched possible local recipes for limewash, NCPTT developed a series of tests for the study. Using published testing standards, researchers determined that abrasion, adhesion, and artificial weathering would provide the most applicable data for determining the most durable limewash. Four separate limes and several recipes were chosen to apply to samples of handmade brick, modern brick, weathered wood, hand-sawn wood, and epoxy.
“We found that our limewash recipes performed better on the brick than the wood and similarly on the wood and epoxy,” Sarah Jackson, NCPTT architectural conservator, said.
“On handmade brick samples where a primer was not applied prior to limewashing the limewash performed better after weathering versus samples with a primer. None of the limewash recipes we tested were durable on wood samples. However, samples with a primer performed better, possibly as a result of wood’s cell structure.”
Jackson has demonstrated limewash application in several venues, including the Traditional Building conference and the International Preservation Trades Workshop.