Reviving Old Brick Walls
As part of a plan to turn our basement into a workshop, we expected to do a two-part restoration: First, remove the thick, failing waterproof paint; second, bring in a professional masonry team to repoint the walls. Although both jobs were labor intensive, our part of the project—removing the paint —took longer than the repointing work, which was no small task.
While pointing methods vary, using the right mortar is about the most important thing you can do when it comes to caring for historic masonry. That’s because historic bricks are inherently soft. The mortar that cushions one brick from another needs to be softer and more permeable than the brick itself. Otherwise, the brick won’t be able to slowly flex during the normal freeze/thaw and expansion and contraction cycles of the seasons.
Most modern mortars are made with Portland cement, which is much stronger and harder than historic lime mortars. It also doesn’t breathe like old mortars. (You want the mortar to let moisture vapor out; otherwise, moisture is forced into the brick or stone, leading to cracks and failure.) Portland-cement mortars can cause the faces of the brick to crack and deteriorate, a condition known as spalling.
Portland-cement mortars didn’t come into widespread use until after 1900. If your home was built before about 1890, it’s likely the mortar is a mix of lime and sand. By the 1930s, masons were using equal parts Portland cement and lime.
There are several historical options on the market that incorporate lime as part of the blend. While our mason, Sean Moore of Moore Stone, typically works with type S lime mortar, we requested he use an Ecologic mortar from DeGruchy’s LimeWorks US. Our old mortar was mixed with sand that had plenty of
natural color variations from stones and other elements. Regardless of the color of the binder or colored additives, the sand is the primary material that gives mortar its color. We chose a mortar that mimicked that look by blending a few different shades of standard Solomon mortar colors, and then adding flecks of coloring.
The paint stripping proceeded so slowly that the masonry team arrived well before stripping was complete. We arranged a work-around so that I could continue without getting in the team’s way.
Removing Old Mortar
First the team removed the old mortar. For best results, mortar should be removed to a depth of 2 to 2 ½ times the width of the mortar joint to ensure an adequate bond. For example, a mortar joint that’s ½ " wide should be removed to a depth of between 1" and 1 ½ ". To cut away the old soft mortar, the traditional method is to use a cold chisel and hammer. Our pros used a variety of scraping tools as well as an angle grinder. They were experts with these tools, so there’s little if any evidence of an errant grinder wheel hitting one of the bricks.
Once old mortar was out of the way, we vacuumed out all debris from the joints. I introduced Moore’s team to a dust shroud for DeWalt angle grinders, which aids in dust collection. Coupled with a dust-extractor vacuum, the shroud cuts down on a good 70 to 90 percent of dust in this normally messy process. Although the shroud is not meant to fit smaller grinders, it works well [ cont. on page 43]