Mating new mortar to old brick requires careful thought, a bit of chemistry, and practiced skills.
- Author:
- Alex Santantonio
- Publish Date:
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While brick has the potential to last 100 years or more, the average lifespan of a well-made mortar joint is about 25 years. The mortar is “sacrificial,” intended to need care.
That was certainly the case with the mortar joints in the basem*nt of the sp1885 row house I share with my wife and restoration partner, Wendy. The brick walls were covered in failing “waterproof” paint, portions of exposed mortar were crumbling, and some rows of brick had become distinctly uneven.
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 ofnatural 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 ifone of the set-screws on the grinder’s locking collar is removed.
Prepping and Filling
Brick and mortar are thirsty creatures. If you put wet mortar on dry brick, the brick will prematurely steal the moisture from the mix. This can cause the new mortar to cure too quickly, ultimately causing cracks and failure. Before repointing, thoroughly wet the joint using a spray bottle or the spray attachment on a garden hose, backed down to a fine mist. The joint should be damp, but not drenched.
The masons preferred to use a mortar bag to squeeze the mortar into the joint, and then strike the joint using a tool to give it a classic concave profile. A more traditional method is to use a pointing trowel. The trowel should be slightly smaller than the joint being filled. If the joint is less than 1″ deep, fill the joint completely and pack the mortar tightly all the way to the back. For deeper joints, fill using successive layers about ¼” deep. Pack the mortar well into the back corners. Once the layer reaches “thumb-print” hardness, add another ¼” layer. When the last layer is applied, overfill the joint slightly. When it too is thumb print-hard, tool the joint to match the historic joint pattern evident in the wall. Avoid dripping mortar on the bricks; the lime in the mix can stain them.
I kept the mortar wet, especially on the party wall, over a two-day period after pointing. I sprayed each wall down every hour or so with a garden sprayer, watching as the mortar slowly took on the light grey color we were expecting. The end result is pretty spectacular. It may still be a basem*nt, but I’d say it’s a basem*nt with walls of great character.
Reviving Old Brick Walls
As part of a plan to turn our basem*nt 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.
PRO TIP: To match the mortar used when the house was built—especially for unusual materials like rubblestone or skintled brick—look for original mortar under eaves or behind pilasters, etc.
Paint Removal
Removing paint from brick is tough. Removing waterproof paint from brick is agonizing. When Wendy and I undertook paint removal in our row- house basem*nt, we used every kind of masonry paint stripper available: environmentally friendly pastes, a soy-based remover, and a caustic stripper, plus steam, heat, and infrared heat. Nothing worked! The strippers just made a mess. The brick appeared to absorb the heat and steam, so the paint never heated up to the point necessary to release or soften. Fortunately, quite a bit of paint came off relatively easily on perimeter walls that were below grade. This is probably because brick exposed to the elements absorbs and releases moisture, fracturing the paint’s bond. Wherever the brick had been repointed with cement mortar and wasn’t exposed (at a party wall, for instance), the paint was like immovable rock. Ultimately, my solution was elbow grease: I ended up using a basic hammer and 5-in-1 multi-tool as a chisel, along with pull scrapers. Then I turned to a handheld drum sander that has different attachments and provides dust collection: a Porter Cable Restorer. Once I got a section of paint well started, I used the paint-removal wheels on the sander to grind down and burn away any remaining paint. —Alex Santantonio
Mortar Joints
When brick, stone, or concrete block are laid, the mortar joint extends across the full width of the masonry unit. Mortar repairs typically discard and refill only an inch or two of the mortar. Every joint is finished with a profile, which is struck into the semi-firm mortar while it’s pliable but not completely fresh. Common profiles include:
CONCAVE The most common mortar joint is one of the easiest to master and provides good weather protection.
WEATHER(ED) In this joint, the mortar is inclined from the bottom to the top of the joint to shed water. The joint surface tends the catch light, giving the brickwork a neat, orderly appearance.
BEADED Used in historical restorations (usually in stonework), the joint projects from the brick, adding a visual element to the masonry.
RAKED Used in many early-20th-century homes, this joint has a lower resistance to weather than others, because it leaves part of the masonry bed exposed.
VEE JOINT Made with a V-shaped jointer, V joints are highly visible, adding an ornamental quality to masonry. They’re also water-resistant because the shape directs water away from the seal.
Point or Tuck?
Removing damaged or deteriorating mortar and repairing the joints may be variously referred to as pointing, repointing, and tuck pointing. Is there a difference? Pointing and repointing are virtually the same thing, although repointing refers to repairs. Both mean adding mortar to a masonry wall.
Tuck pointing is, however, something different. The term (which may be hyphenated or expressed as a single word) first referred to the joints laid between the rough-shaped, irregular bricks common in 18th-century England. Typically, the joint was filled with colored mortar tooled with a narrow groove, the groove then filled with a slightly white lime putty. The process creates the appearance of finer mortar joints.
Brick by Brick
Matching mortar to historic brick is much easierwhen you can identify the type of brick you have.There are three recognizable types: soft-mud brick, pressed brick, and wire-cut brick.
- Soft mud bricks, in use before the 1860s, were made by hand-packing clay into wood moulds, then firing them in wood- or coal-burning kilns. The bricks are soft, with inconsistencies and irregular edges that give them character. Recommended mortar: 1 part lime to 3 parts sand. Cover and wet for 72 hours before use; to speed the curing process, add about ¼ part lime.
- Pressed brick was first made in the mid-19th century; clay was pressed into moulds by machine, then fired in hotter kilns. Recommended mortar: 1 part Portland cement, 2 parts lime, 8–9 parts sand.
- Wire-cut bricks appeared in the late-19th century. Clay is mechanically extruded, then cut into brick shapes by wires. Wire-cut brick may or may not have holes. Recommended mortar: 1 part Portland cement, 1 part lime, 6–7 parts sand.
Repointing mortars for stone—a natural material—vary more widely than those for brick. Generally, the harder the stone, the harder the mortar (mortar still should be softer than the stone).
Brick & Mortar Resources
- American Building Restoration Products Masonry & fireplace cleaners & strippers
- AMR Labs Mortar analysis
- Construction Materials Consultants Mortar analysis
- DeGruchy’s Limeworks US Breathable lime mortars, mortar analysis
- Dumond Chemicals Masonry strippers (PeelAway, Smart Strip)
- Franmar Paint removers, surface cleaners
- Larsen Products Concrete & plaster bonding systems
- Moore StoneArtisanal masonry, Washington, D.C. area
- Old Carolina Brick Handmade brick, pavers, Thin Brick
- Package Pavement Historic lime mortars, other concrete products
- Pine Hall Brick Face brick, clay pavers
- Preservation Products Masonry sealer
- Prosoco Sure Klean masonry cleaner
- Quikrete Cement & concrete products
- Rutland Products Cements & masonry cleaners
- Sakrete Mortar, concrete & stucco mixes; color additives
- Solomon Colors Standard & custom mortar colors
