Repair and restoration of masonry on 19th century and older buildings must be undertaken with great care and understanding of the properties of the masonry components. Masonry structures have been built with a mortar of lime and sand for thousands of years and, in some instances, right up to the early part of the 20th century. Repairs such as pointing, cleaning, brick and stone replacement and stone patching are an important part of maintaining historical buildings, but inappropriate mortar, cleaning, and sealants are a major cause of damage to historical masonry buildings.
The process begins with the proper analysis of the problem, followed by use of the correct materials along with skilled workmanship to apply those materials. Durable Restoration personnel are trained in the use of these historical materials and methods. Our personnel have been trained and certified by U.S. Heritage for use of lime putty mortar, as well as Cathedral Stone, for use of Jahn mortar in repair of natural stone, terra cotta, brick, plaster, and stucco.
To ensure correct handling and solutions to historic masonry problems, our personnel perform such diagnostics as product trials, mortar analysis, and more in-depth analysis such as impulse radar or ground-penetrating radar (GPR) to get an accurate assessment of the masonry’s condition.
Julie Butler, Preservation Director for DRC Mid-Atlantic, sharing information about brick and mortar restoration while on-site at 88 State Circle, Annapolis, MD.
What is masonry cement?
Masonry cement is a mixture of Portland cement, ground limestone and air entrainment (in the form of soap). This mixture creates a mortar with properties that can actually damage historic brick.
Masonry cement is hard and inflexible. Because the bricks on historic homes are softer than modern cement, bricks may be damaged as the wall moves and shifts. It traps moisture (is vapor impermeable) which can cause the face of the brick to explode. It also has a lower bond strength, which results in a poorer bond to the brick.
Why use lime mortar with historic brick?
Lime mortar is made of burned limestone, rather than ground limestone. This burning process is what gives lime mortar the properties that are required for historic masonry restoration. Lime mortar has low compression strength and high flexibility. It absorbs movement and protects the bricks from the effects of settling and expansion and contraction.
Lime mortar is vapor permeable making it capable of relieving moisture which has been absorbed by the bricks. Lime particles are much smaller than Portland cement particles, resulting in greater bond strength to masonry units. It does not require air entrainment, so it adheres better and remains more leak resistant. It is also self-healing; moisture from rain causes small cracks to knit back together. Lime mortar absorbs more water than masonry cement, which will help keep the inside of your building dry.
The choice is yours!
For historically correct masonry repair that will look good and stand up to time and the elements, choosing the right mortar is as important as choosing the right historic masonry contractor. The Durable Restoration Company is certified and trained by The U.S. Heritage group for the application of lime mortar. We understand the unique properties of historic masonry including finding the appropriate mortar mix for your property; proper preparation of the masonry joints to make the repair last as long as the original masonry; and matching the existing mortar, especially when spot-pointing small areas on a wall.