Repointing Mortar – Preservation Café

Posted on April 19th, 2016 by Elizabeth Nelson

To repoint, or not to repoint: that is the question! Mortar may be the most over-looked and under-appreciated aspect of your row house. Architectural conservator Justine Posluszny Bello discussed mortar and repointing fundamentals for the Capitol Hill homeowner at a Preservation Café, Thursday, April 21, 2016, at Ebenezers Coffeehouse.The April Preservation Cafe featured local architectural conservator and Capitol Hill resident, Justine Posluszny Bello, speaking on the issues associated with pointing historic brick rowhouses. Ms. Bello premised the talk on the idea that the questions surrounding how, why or why not to re-point historic brick are not straightforward and rely greatly on context.

People often use the phrase “brick and mortar” to describe a structure of substance, heft, value and importance. Although “mortar” represents one-half of this phrase, most people give far more attention to the “brick.” Ms. Bello stressed that although a humble building material in some ways, a properly designed, mixed and installed mortar is critical to the structural integrity of any building. Ms. Bello provided some brief historical context of mortar and how it has—and has not—changed over the years.

Ms. Bello then described how many modern mortars can interact negatively with the brick, meaning that moisture and salts end up trapped within the brick; with no place to go, the brick building material ends up becoming damaged. She elaborated on the relationship between brick and mortar: mortar should, usually, be “sacrificial” to the brick. This means that if you have to choose, you’d rather your pointing mortar fail first, before your brick. This is because it’s a lot easier to replace some failed mortar by repointing than to replace failed brick. She explained that many modern mortars rely heavily on the use of Portland cement, a component that can end up being too hard, dense and not “breathable” to be used with the historic bricks in many historic Capitol Hill homes. A more traditional mortar would be based on the use of a lime putty or “quick lime,” which is softer and yields a more porous mortar.

That said, Ms. Bello discussed that it might be too simple to characterize all modern mortar
as “bad” or “destructive” and instead to consider the question of appropriateness: finding an appropriate mortar that is compatible with a specific type of brick (and yes, there are many different types of bricks with different qualities out there) from both a historical and a physical/technical perspective. Ms. Bello listed some of the resources available to homeowners to help them make informed decisions concerning their specific property: Technical Preservation Briefs published by the National Park Service, knowledgeable and reputable contractors, technical representatives at masonry and mortar mix companies themselves, third-party consultants and experts and of course CHRS.

Repointing and masonry repair requires a permit within the Capitol Hill Historic District for many of the reasons just cited — too hard a mortar can damage the bricks and some of the houses with the thin butter joints were originally laid with mortar tinted with lamp black so they had a very dark aspect that contributed very smooth, monolithic appearance of the front facades.  Other houses or structures (particularly walls, porches, garages) may have had special mortar joint treatments (raked joints in the yellow/brown brick porch front houses, aforementioned butter joints, toothpaste joints in the stone walls for instance).  So when people are doing repointing and repair they (or preferably their contractor) should bring in photos so the Historic Preservation Office staff can see existing conditions and talk about mortar type, color, and “special effects”.

If a person is simply painting with no masonry repair, a permit is not required. In any case, it’s important to familiarize yourself with the local laws in your community to understand what is regulated and what is not and in turn, to use all the information you’ve collected to make informed decisions that are good for the longevity your historic treasure.