Historic Preservation Using Traditional Lime Mortars

Historic Brick Repointing
If you live in a historic home in areas of the U.S. such as North Carolina, Pennsylvania, Virginia and Washington, D.C. which has crumbling brick work or the mortar needs to be repointed, you may require lime mortar. Make sure you work with a contractor familiar with the use of traditional lime mortars. There are basically two types of mortar: the readily available Portland cement and traditional lime mortar. Many masons are familiar with using inexpensive Portland cement but its application can potentially result in damage to your home’s faÃ?§ade if your home was built before the 1920s when soft brick and lime mortars were primarily used.

How Does Historic Lime Mortar Function?
One of the functions of mortar is to allow moisture to migrate out of masonry through the softest points. Portland cement tends to function more like a glue to simply hold bricks in place. When the mortar is impermeable and hard like Portland cement, water will naturally gravitate to the softer historic brick where the masonry is then continually exposed to damaging winter freeze and thaw cycles which can lead to deterioration and decay. Traditional lime mortars are softer and more flexible than brick and act as a sacrificial material for moisture to migrate, according to Virginia Lime Works, makers of traditional lime mortars.

Hydraulic vs. Hydrated Lime
If you ask a contractor if they use lime mortar they may still answer “yes” as Portland cement includes lime. Further, builder’s hydrated lime used to lay brick and concrete blocks is different than hydraulic lime and will not yield the same results. On the other hand, the natural hydraulic limes recommended in historic preservation have a high calcium lime content of 95-100% pure calcium carbonate. While magnesium and dolomite limes are two other available limes, insist on high calcium lime which has the added benefit of functioning as a reactive self-healing lime. Over time as the mortar develops hairline cracks, there is a chemical reaction which occurs between the carbon dioxide and moisture in the air which combines with the lime within the mortar to seal its own cracks.

Repointing
When it comes to repointing you want to make sure the job is done right as it should last 25 to 30 years while improper repointing can cause irreversible damage. Repointing sometimes called “pointing” or “tuckpointing” is the process of removing deteriorated mortar from joints between masonry units and replacing it with new mortar. Before embarking on any repointing project, investigate other causes of deterioration such as leaking roofs, gutters and downspouts or foundation issues with settlement of the building.

When to Do the Work
The ideal time to talk to a contractor to schedule work is when the weather is temperate. According to Virginia Lime Works, “as a good rule of thumb, if the mason is comfortable then the wall is comfortable”. Otherwise on hot or freezing days, extra precautions need to be taken to ensure the mortar is properly cured.

Historic Brick Restoration
If you have decaying brick walls, you want to select a contractor who has an understanding of historic masonry. One contractor in the District of Columbia area for example is Danny Palousek of Pointing Plus, a self-proclaimed “brick nerd” who goes to the extreme of hoarding old bricks at his brother’s house in Maryland for future restoration jobs. Danny is so enthusiastic about his craft that he went to castle in northern Wales to participate in a work/study program and has appeared on the PBS show “This Old House” where he participated in the rehabilitation of a brick rowhouse.

Recommendation To Find a Contractor
Because historic brick restoration is a costly endeavor, Danny recommends homeowners talk with potential contractors to assess the appropriate mortar and materials for restoration, evaluate the mason’s experience and understanding of historic lime mortars and preservation issues, obtain references and request to see a portfolio of pictures from job sites.

Additional Information

“Repointing Mortar Joints in Historic Masonry Buildings”
Preservation Briefs
National Park Service

Virginia Lime Works
Makers of Traditional Lime Mortars