Chimney Masonry Repair and Repointing

How chimney masonry wears out

Brick and mortar both absorb water. In a New Jersey winter, that water can freeze inside the masonry, expand and push the material apart a little at a time. After enough cycles the mortar joints turn sandy and recede, and the faces of some bricks start to break off. That flaking is called spalling.

Once joints open up, more water gets in, so the damage tends to speed up rather than hold steady. A chimney stands exposed on all four sides above the roof, which is why its masonry usually shows wear long before the walls of the house.

What to look for from the ground

• Mortar joints that look recessed, sandy or hollow compared with the brick face
• Brick faces that have flaked, cracked or fallen away, sometimes with fragments on the roof
• White powdery staining (efflorescence), which shows water moving through the masonry
• Cracks that step diagonally through the joints
• Bricks that look loose near the top of the chimney

Binoculars help. None of these signs on its own tells you the cause or how deep the damage goes. Spalling on the top few courses, for example, often traces back to a failing crown above it.

How we assess it

We look at the masonry from the roof when it's safe to get up there, and note which faces and which courses are affected. We check the crown, cap and flashing at the same time, because water from those parts is a common reason masonry fails. Inside, a chimney camera where the flue allows shows whether water damage has reached the flue lining. In the attic, when it's safe and accessible, we look for wet framing or staining around the chimney.

You get photos and a description of what we found, with the repair options, before any work is scheduled.

We also note how the chimney is built: solid brick, brick with a stucco or parged face, or stone. Each handles water and repair materials differently, which affects the options.

Repointing: replacing worn mortar

Repointing means removing deteriorated mortar from the joints to a sound depth and packing in new mortar in layers. Done properly, it restores the joints so they shed water and hold the brick in place. The National Park Service's guidance on historic masonry recommends removing old mortar to a depth of roughly two to two and a half times the joint width, so the new mortar bonds well and doesn't pop out.

Why the mortar has to match the brick

Mortar should be the weaker, more breathable part of the wall. If new mortar is harder and less permeable than the brick around it, stress and moisture end up moving through the brick instead, and the brick spalls. This is a real risk on older homes, where softer brick and lime-rich mortar were common. A hard modern cement mix pointed into that brick can do more harm than good.

So part of the assessment is judging what the existing brick and mortar are, and choosing a mortar that's compatible in strength and texture. Our guide to repointing vs. tuckpointing explains the terms, which are often mixed up.

Replacing damaged brick

Individual spalled or cracked bricks can be cut out and replaced. Finding a replacement that matches in size, color and hardness matters for appearance and for how the brick handles water. Salvaged or carefully selected brick is often a better match on an older chimney than a new standard brick. When the damage is spread across many bricks on the upper courses, rebuilding that section usually gives a better result than replacing bricks one at a time.

Replacement bricks also have to suit the location. Brick above the roof faces more water and freeze-thaw than brick inside an attic or along a sheltered wall, so a brick that looks right but absorbs a lot of water can fail early on an exposed chimney.

When masonry repair isn't enough

After repairs, a vapor-permeable water repellent can slow water absorption. That's covered on our waterproofing page. It belongs after repair, not in place of it.

Limits and what affects the scope

• Color match. New mortar and replacement brick won't match weathered masonry exactly on day one.
• Weather. Mortar work needs suitable temperatures and dry conditions to cure, so timing can shift in winter.
• Hidden damage. Brick that looks sound can turn out loose once neighboring joints are opened.
• Access and height. Tall chimneys, steep roofs and multiple faces add to the work.
• Historic homes. Matching period materials can take longer. See chimneys on historic homes.

Next step

If you're seeing receding joints, flaking brick or white staining on your chimney, request an assessment. A photo from the ground or a window helps. A team member will contact you to confirm a time.

Request a masonry assessment

Questions homeowners ask

Sources

1. National Park Service, Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings