What kind of brick should be used when replacing damaged chimney bricks to match the originals?

Matching replacement bricks to the originals on a chimney requires careful attention to colour, texture, size, and — most importantly — the brick's compressive strength and porosity, because mismatched brick can cause structural and moisture problems beyond just looking wrong. Finding a good match is one of the trickiest aspects of chimney repair on older GTA homes, and it is worth taking the time to get it right.

The first step is to identify what type of brick your chimney is made from. GTA homes span well over a century of construction, and the brick types vary enormously. Pre-war homes (before 1945) in established Toronto neighbourhoods like Cabbagetown, the Annex, Roncesvalles, and Riverdale typically have soft clay bricks made in local Ontario brickyards. These bricks are softer, more porous, and have more colour variation than modern bricks. They were designed to work with lime-based mortar — the brick absorbs and releases moisture freely, and the soft mortar acts as a sacrificial element that deteriorates before the brick does. Post-war homes (1945-1975) across Scarborough, North York, and Etobicoke generally have harder pressed or extruded bricks that are more uniform in colour and size. Modern homes (1980s onward) typically have engineered wire-cut bricks with very consistent colour, texture, and dimensions.

How to find matching bricks: Start by removing one intact original brick from a less visible area of the chimney (such as the back side, below the roofline) and take it to a brick supply yard that specializes in matching. In the GTA, there are several brick suppliers and salvage yards that stock reclaimed heritage brick from demolished Toronto buildings — this is often the best source for matching pre-war brickwork because the bricks were made from the same local clay in the same era. Reclaimed brick typically costs $1.50 to $4.00 per brick in the GTA, compared to $0.75 to $2.00 for new brick. New manufactured brick can be custom-ordered to match specific colours and textures, but minimum order quantities and lead times (4 to 8 weeks) make this practical only for larger projects.

Critical technical considerations: The replacement brick must have similar compressive strength and porosity to the surrounding original bricks. Installing modern high-strength, low-porosity bricks in a chimney made of soft heritage bricks creates a hard spot that redirects moisture and freeze-thaw stress to the adjacent softer bricks, accelerating their deterioration. This is the same principle as using the wrong mortar type — the mismatched element causes damage to the surrounding original material. For heritage chimneys, soft clay bricks with a compressive strength in the range of 15 to 25 MPa are appropriate. For post-war and modern chimneys, standard grade bricks rated at 30 to 50 MPa are typical.

Brick dimensions matter too. Standard modern modular brick in Ontario is approximately 190mm long by 90mm wide by 57mm tall (7.5 by 3.5 by 2.25 inches). However, older Toronto bricks were not standardized and can vary significantly — imperial-size bricks from the pre-war era are often slightly larger or smaller than modern modular brick, and the mortar joint thickness was adjusted accordingly. Measure several original bricks on your chimney (length, width, and height) and bring these measurements to the supplier. Even a 5mm difference in brick height becomes very visible over multiple courses because the mortar joints must compensate, and inconsistent joint widths look obviously wrong.

Mortar matching is equally important. The mortar colour and joint profile should match the existing chimney work. For heritage chimneys, lime-based mortar (Type O or Type K) must be used — never Portland cement mortar on soft brick, as it will cause the original bricks to spall. Your mason should be experienced with heritage brickwork and mortar matching. The mortar joint profile (concave, flush, weathered, struck) should match the original as well.

This is professional work. Chimney brick replacement involves working at height, cutting out damaged bricks without disturbing surrounding brickwork, matching mortar type and colour, and achieving a weather-tight finished product that blends with the original. An experienced mason with WSIB coverage who specializes in chimney and heritage brickwork is essential. Expect to pay $50 to $150 per brick for removal, matching, and replacement installed, depending on accessibility and the number of bricks being replaced.