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Lime Mortar is the Perfect Partner For Old Brick

Nov 8, 2018 6:02:49 PM Christina Wilson

For owners of many historic homes in Washington DC, brick mortar repair is necessary to maintain the integrity and value of the old structures. This type of brick restoration involves the craft of removing the old mortar and replacing it with new mortar. Sometimes deterioration of the old brick walls is the result of repairs with the wrong materials.

Here’s what the team at This Old House has to say about one badly deteriorating old brick façade and the “delicate balance” required between brick and mortar:

The mortar is killing it. Not the original mortar, a relatively soft mix of lime and sand, but the previous patch job, which used masonry cement. The old lime-based mortar had been a perfect partner for the soft, porous brick, flexing to accommodate the brick's slight expansion and contraction. Like all mortars, however, it slowly eroded, and after 60 or 70 years the weathered portion was chiseled out and replaced, a process called repointing (or tuckpointing).

Unfortunately for this wall, masonry practices underwent a tectonic shift in the 1930s. Brick became harder and more rigid, as did mortar. With the ready availability of Portland cement masons abandoned time-consuming lime-based mortars, which set so slowly that no more than seven courses could be done in a day. Instead, bricklayers adopted fast-setting masonry cement: sand and ground limestone blended together with as much as 65 percent portland cement.

That modern mix was the unyielding cement the previous masons had slapped on the house joints. Once it cured, the delicate give-and-take of brick and mortar was replaced by a protracted battle-which the old brick was losing. The cement dammed the joints, trapping moisture inside the brick.

In winter, the waterlogged walls froze and cracked, allowing still more water to penetrate. In summer, as the brick tried to expand, its protective fire-skin literally popped off. The cement mortar is not helping the wall; it is actually hurting the wall.

Source: TOH, Repointing Brick


Renaissance Development, a leader in brick restoration and historic preservation, specializes in the restoration of a historic brick building’s mortar joints using traditional methods (tuckpointing) and materials. Contact us for a free site visit and project quote. 

 

Categories: Restoration, Historic Preservation

 

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