Chimneys on Historic Homes

Why older chimneys need a different approach

Many chimneys built before the mid-twentieth century were laid with high-lime mortar and brick that was often softer and more porous than modern brick. These materials were designed to work together: moisture moves through the mortar and brick and dries out, and the mortar, being the softer part, wears first and can be renewed.

The National Park Service notes that most buildings with masonry exteriors, and most others too, have masonry foundations or chimneys, so these principles apply to a great many homes, not just museum buildings.

Mortar: softer is safer

The NPS guidance on repointing historic masonry is clear that new mortar should be softer or more permeable than the masonry units and no harder or less permeable than the historic mortar. When mortar is harder than the brick, movement and moisture stress go into the brick instead, which can crack or spall it permanently.

The same guidance describes lime mortar as soft, porous, and stable through temperature swings, and says masonry cement products are generally not recommended for historic masonry because they are too strong. Analysis of the original mortar, or at least a careful look at its color, texture, and hardness, is part of planning. See repointing vs. tuckpointing.

Matching appearance

• Sand drives most of the mortar's color and texture.
• Joint profile should match the original tooling.
• Joint width should not be widened by careless grinding. NPS favors hand tools for removing old mortar from historic masonry because they pose the least risk to brick edges.
• Replacement brick should match the size, color, texture and durability of the original. NPS notes that the masonry should be examined so any replacement units match.

NPS recommends judging a new mortar match against unweathered original mortar after the new mortar has cured.

Coatings and cleaning to avoid

NPS guidance states that a water-repellent coating is not a recommended treatment for historic masonry unless there is a specific problem, and that most historic masonry has survived for decades without one. Waterproof coatings that seal the surface can trap moisture. If water is a problem, the causes are usually leaking roofs, clogged gutters, missing mortar, or a failed crown or cap, and those should be fixed first. See do chimney sealers work?

Cleaning should be gentle. NPS recommends low-pressure water and natural bristle or nylon brushes, and warns that acid cleaners should never be used on dry masonry. High-pressure washing and abrasive blasting can erode soft brick faces.

Local historic review in New Jersey

Many New Jersey municipalities have a historic preservation commission. The New Jersey Historic Preservation Office's guidance for its local government preservation program describes commissions that review applications for alterations, demolitions and new construction affecting designated landmarks and historic districts, based on written standards. Towns such as Montclair issue a certificate of appropriateness to approve certain changes to local landmarks and properties in local historic districts.

What needs review is set by each town's ordinance. Changing a chimney's appearance, rebuilding it with different brick, removing it, or adding a visible metal cap or liner termination may be covered. Before exterior chimney work on a home in a local historic district or a designated landmark, check with your town's historic preservation commission or zoning office. Routine like-for-like repairs may be treated differently from visible changes.

Keeping an old chimney working

Historic chimneys often have unlined flues, very large flues, or flues that were designed for fuels no longer used. If the chimney will vent an appliance or a working fireplace, it needs to meet current safety expectations, which may mean relining. Liners that sit inside the chimney can often be installed with little change to the exterior, apart from a cap at the top. See liner options.

Old chimneys can also have hidden problems: deteriorated interior brick, past fire damage, or framing too close to the masonry. CSIA's Level 2 inspection, which includes a video examination of the flue, is recommended on the sale or transfer of a property and when appliances change.

Caps, crowns and other visible additions

Some of the most useful protective work on an old chimney is also visible. A cap over the flue, a reshaped crown, new copper or lead-coated flashing, or a liner termination all change how the top of the chimney looks. Choosing low-profile caps, matching metals to the roof and trim, and keeping decorative chimney pots or corbelling intact can protect the masonry without changing the character of the house. Where local review applies, these are the details a commission is likely to ask about, so bring photos and product information.

Repair first, rebuild with care

Preservation practice favors repairing over replacing. On a historic chimney, that means repointing, replacing only damaged brick, and rebuilding the crown before considering a rebuild. When a rebuild is unavoidable, salvaging and reusing sound original brick, matching the original corbelling and details, and using compatible mortar keep the chimney's character. See repair or rebuild a chimney?

How we approach older chimneys

We start with an assessment of the masonry, mortar, crown, cap, flashing, and flue, using a chimney camera when the flue allows and checking the attic side when safe and accessible. On older homes, the conversation includes mortar type, brick matching, and whether local review may apply. You receive findings with photos before any repair is scheduled, which can also help if your town asks for documentation.

Next step

Request an assessment, and see our masonry repair and repointing and chimney rebuilding and restoration services. You can also find your town on our New Jersey service areas page.

Questions homeowners ask

Sources

1. NPS Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings
2. NPS Preservation Brief 1: Cleaning and Water-Repellent Treatments for Historic Masonry Buildings
3. NJ Historic Preservation Office: Certified Local Government guidelines
4. Township of Montclair, NJ: What is a Certificate of Appropriateness?
5. CSIA: The Three Levels of Chimney Inspections

This guide is general information. It can't diagnose a specific chimney; an inspection can.