How do I repoint old brick mortar?

To repoint old brick, you rake the crumbling mortar out of the joints, clean them, and pack in new mortar that is softer than the brick. Most of the skill is in three choices: fixing the cause before you start, picking the right mortar, and removing old mortar without chipping the brick.

Fix the cause first

Failing mortar is often a symptom. The National Park Service's repointing guidance names the usual root causes: leaking roofs or gutters, settlement of the building, rising damp or extreme weather exposure.^[1] It also warns that repointing alone will not solve problems that come from somewhere else,^[1] so check gutters, downspouts and the slope of the soil before you buy mortar. See why gutters overflow if water is spilling down the wall.

The Park Service lists the usual signs that a wall needs repointing: disintegrating mortar, cracks in mortar joints, loose bricks or stones, damp walls.^[1] Cracked or spalled brick is a different matter, since new mortar will not cure it, and a crack that steps across the wall or runs through bricks may point to movement in the building; read why a brick wall cracks before you fill them.

Choose a mortar softer than the brick

This is where most DIY repointing goes wrong. The rule in the Park Service's guidance is that the new mortar must be softer and more vapor permeable than the brick, and no harder or less permeable than the old mortar.^[1] Mortar is meant to be the sacrificial part of the wall. A mortar stronger than the brick will not give, so the stress goes into the brick instead, cracking and spalling it in ways that are hard to repair.^[1]

Age matters. Buildings put up between 1873 and 1930 can have anything from pure lime and sand mortar to a mix of lime, portland cement and sand,^[1] and before the late 19th century, lime was the main binder.^[1] Mortar types are graded by strength: Type M (2,500 psi), Type S (1,800 psi), Type N (750 psi), Type O (350 psi) and Type K (75 psi).^[1] Softer old brick calls for the softer end of that range, and Type N is the usual choice only when the brick is hard and modern.

Read the bag. QUIKRETE Mortar Mix, for example, is a blend of masonry cement and graded sand that meets ASTM C270 as Type N mortar.^[4][3] That is reasonable for a house built with modern hard brick, but masonry cement makes high-strength mortar and generally is not recommended for historic masonry.^[1] For soft, old brick, look for a lime-rich mix and match the colour and texture of the sand to the old joints.

Remove the old mortar without hurting the brick

The Park Service calls a hammer and chisel the least damaging way to remove old mortar.^[1] It warns that power saws on thin brick joints almost always break brick edges and overcut the vertical joints.^[1] A narrow plugging chisel and a light hammer are slow, but they leave the brick intact.

Rake each joint out to a depth of at least 2 to 2½ times the joint's width, which for most brick joints is about ½ to 1 inch,^[1] and keep going past that wherever the mortar is still loose. Leave the back of the cut square and clear thin slivers of mortar off the brick edges so the new mortar can grip.

Grinding mortar makes silica dust. OSHA's construction silica rule pairs handheld grinders used for mortar removal with a grinder fitted with a commercial shroud and a dust collection system,^[6] which is one more reason homeowners do better with hand tools.

Fill, tool and cure

Pick the day. Aim for wall temperatures between 40 and 95 degrees F^[1] and work in the shade. Rinse the joints so they are damp, with no standing water, when you fill them.^[1] Use each batch within about 30 minutes of final mixing and do not add more water to stiffening mortar.^[1]

Pack the mortar in layers about ¼ inch thick,^[1] each pressed into the back corners and left to reach thumbprint hardness before the next. Timing the tooling matters: If tooled too soft, the joint dries lighter and can show hairline cracks; tooled too hard, it can show dark streaks and will not close tightly against the brick.^[1] Match the profile of the old joints, and on worn, rounded brick keep the mortar slightly recessed so the joint does not look wider than it is.

Clean up with a stiff natural or nylon brush. The Park Service says: "Metal bristle brushes should never be used on historic masonry."^[1] Skip acid cleaners on new work, too; muriatic acid is generally ineffective on efflorescence and can bring out more salts.^[1] White bloom on new joints often weathers off on its own.

Done carefully, the work lasts. A good repointing job is meant to last at least 30 years, and preferably 50 to 100.^[1]

Protect yourself

Wet mortar is caustic. The safety data sheet for QUIKRETE's masonry mortars warns that it "Causes severe skin burns and serious eye damage"^[5] and that burns from portland cement may not hurt right away, so pain will not warn you.^[5] Wear nitrile gloves, long sleeves and eye protection, and wash off any mortar on your skin promptly. The same sheet warns that the dry product "May cause cancer through chronic inhalation"^[5] because of its silica, so pour and mix outdoors, upwind. For mixing, the sheet recommends a NIOSH-approved dust mask or filtering face piece in poorly ventilated areas or when permissible exposure limits may be exceeded.^[5]

Permits and historic districts

Virginia's Uniform Statewide Building Code applies statewide. It requires a permit for work that involves removing or adding any wall or portion of a wall, or any structural component,^[7] and it exempts ordinary repair work that the building official deems minor and ordinary and that does not adversely affect public health or general safety.^[7] Whether a repointing job counts as minor and ordinary is the building official's call, so ask your city or county building office before a large job or one that includes rebuilding part of a wall.

A local historic district can add its own review. In Martinsville's historic districts, for example, the city's guidelines say mortar joints of brick buildings should keep their original profile, width of joint, colour and style,^[8] and changes that are not in-kind repairs need a Certificate of Appropriateness from the city's Architectural Review Board.^[8] If your house is in a district elsewhere, ask that locality's review board what it covers.

Stop and call a pro if

• The joints are on a chimney, or above what you can reach standing on the ground.
• Brick is bulging, leaning or loose over an area, rather than just the mortar.
• Cracks run through the bricks, step diagonally across the wall, or keep reopening after repair.
• Brick faces are spalling widely, or there are rust and corrosion stains on metal elements^[2] such as the lintel over a window.
• The house is in a local historic district, or the job has grown into rebuilding part of a wall.

Getting help on Loclis

If the job is bigger than a weekend, see what repointing costs in Virginia and whether to hire a mason or a general contractor. You can browse concrete and masonry services, look up masonry and hardscaping businesses around Blacksburg, read the other exterior answers, or describe the brick repair once and let licensed local businesses quote it.