Restoring Older Brick Buildings: Repointing, Cleaning, and Structural Repair

Understanding Why Brick Deteriorates

Brick masonry in Canadian climates faces a specific combination of stresses. Freeze-thaw cycling is the dominant physical force: water absorbed into brick and mortar expands when it freezes, generating internal pressures that, over many cycles, cause the face of the brick to spall — delaminate in layers — and mortar joints to crack. The severity depends on the porosity and saturation of the masonry, which in turn depends on how well moisture is managed by flashings, copings, and drainage detailing.

The second major factor is mortar incompatibility introduced during past repairs. As discussed in the history article, Portland cement mortar applied over original lime-mortar joints transfers movement stress into the brick units rather than absorbing it in the joint. Many Canadian urban buildings that appear to be in poor condition are suffering primarily from incompatible repair materials applied in the mid-20th century rather than from failure of the original 19th-century construction.

Salt crystallization, biological growth, and atmospheric soiling are additional deterioration mechanisms. None of these is as structurally consequential as freeze-thaw damage or mortar incompatibility, but they affect the building's appearance and can accelerate deeper damage if left unaddressed.

Condition Assessment Before Any Work Begins

Before any restoration work is scoped or priced, a systematic condition assessment of the masonry is necessary. This typically involves:

• Visual inspection from close range — either from scaffolding or via rope-access survey — to map crack patterns, spalling, staining, efflorescence, and failed joints.
• Sounding the brick faces with a small hammer to identify delaminating areas that may not be visible from the surface.
• Mortar sampling and laboratory analysis to determine the composition of original mortar and any subsequent repair mortars. This drives the specification for repointing mix design.
• Review of any existing documentation, including prior assessment reports, permit applications, and heritage designation records that may specify approved materials or methods.

On a designated heritage property in Canada, the condition assessment should also identify whether the planned restoration requires a Heritage Permit under the applicable municipal or provincial designation. See the article on heritage designation for how that process works.

Repointing: The Most Common Restoration Task

Repointing — removing deteriorated mortar from joints and replacing it with fresh mortar — is the most frequently performed maintenance task on older brick buildings. Done correctly, it extends the service life of the masonry by decades. Done incorrectly, it accelerates deterioration by introducing incompatible materials or by damaging brick arrises during the raking process.

Mortar Removal

The existing mortar in a joint to be repointed must be removed to a depth of at least 19 millimetres — roughly two and a half times the nominal joint width — to provide enough surface area for the new mortar to bond mechanically. For lime-mortar joints, the mortar can often be removed with hand tools: cold chisels, raking chisels, and occasionally a grinder with a mortar-raking blade, used carefully. The critical constraint is that the tool must not contact the brick arris — the sharp edge where the mortar face meets the brick face. Damage to brick arrises with grinders is permanent and highly visible.

For Portland cement repair patches applied in earlier decades, removal is more difficult because the material is extremely hard. Grinders are sometimes unavoidable, but the risk of brick arris damage increases substantially. Experienced masons can often hand-chisel out old Portland cement patches if the material is worked slowly.

Mortar Mix Specification

The replacement mortar must be compatible with the brick — specifically, it must be no harder in compressive strength than the brick units being repointed. For most 19th-century Canadian brick, this means a Type O or Type K lime-based mortar: a mix of non-hydraulic or lightly hydraulic lime, well-graded sand, and water, with no Portland cement addition. The Parks Canada Standards and Guidelines for the Conservation of Historic Places in Canada specifies this requirement explicitly and provides detailed guidance on mortar selection based on brick porosity and compressive strength testing.

Sand selection matters significantly. The colour and texture of the aggregate in the mortar mix determines the visual appearance of the finished joint. Laboratory analysis of original mortar samples — which identifies both the binder type and aggregate characteristics — makes it possible to formulate a replacement mix that matches the original colour and texture closely. On heritage buildings where the mortar joint is part of the identified heritage attributes, a close visual match is not optional.

Application and Curing

Lime mortar requires damp curing — keeping the freshly pointed joint moist for several days after application — rather than the dry-fast cure appropriate for Portland cement. In Canadian conditions, this means avoiding repointing in hot dry weather without misting, and avoiding freeze conditions until the mortar has had time to carbonate. Most masonry contractors in Canada specify a minimum ambient temperature of 5 degrees Celsius and rising during application and for at least three days after.

Replacing Spalled or Damaged Brick Units

Where individual brick units have spalled, cracked through, or deteriorated beyond the point where they can contribute to weather resistance, replacement with matching units may be necessary. The difficulty on 19th-century Canadian buildings is sourcing brick that matches the original in size, colour, surface texture, and porosity. The kilns that produced much of Canada's historic brick are long closed.

Several salvage suppliers across Canada maintain inventories of recovered brick from demolished buildings — Toronto alone generated large salvage volumes from demolitions in the 1960s and 1970s. For projects where salvage material is unavailable, some heritage consultants and conservation contractors use custom-manufactured reproduction brick produced by a small number of North American and European manufacturers. The reproduction brick must be tested to confirm it is no harder in compressive strength than the original surrounding units.

On designated heritage properties, replacement brick specifications are typically subject to Heritage Permit review and must be approved before installation. Submitting mortar and brick samples with a mock-up panel for approval by the heritage planner before full-scale work begins is standard practice.

Cleaning Brick: What Is Safe and What Causes Damage

Soiled or stained brick facades are sometimes cleaned as part of a restoration project. The choice of cleaning method is critical: aggressive cleaning techniques have destroyed the surface of irreplaceable heritage masonry on numerous Canadian buildings, leaving a pitted, roughened surface that holds more dirt, absorbs more water, and weathers faster than the original face.

• Low-pressure water washing: The safest starting point for general soiling. A hand-held lance delivering water at under 500 psi, combined with a soft natural-bristle brush, removes surface grime on most brick without abrading the surface.
• Chemical cleaning: For biological growth (moss, lichen), a diluted biocide application followed by a dwell period and low-pressure rinsing is effective. For atmospheric staining and light calcium deposits, pH-neutral masonry cleaners are used. Acidic cleaners — including diluted muriatic acid — are used only on specific stain types and must be pre-wetted, carefully neutralized, and completely rinsed. Acid cleaning of soft or lime-heavy brick can dissolve the lime content, permanently weakening the surface.
• Abrasive methods: Sandblasting and high-pressure dry or wet abrasive cleaning are generally prohibited on heritage masonry in Canada. These methods remove not just staining but the dense fired surface of the brick, exposing the more porous interior to accelerated water absorption. The results are often not immediately obvious but cause accelerated deterioration over the following decade.

Addressing Structural Cracks and Movement

Visible crack patterns in brick masonry usually indicate underlying structural movement: foundation settlement, thermal differential, lintel deflection over openings, or roof thrust. Repointing a crack without addressing the movement source results in the same crack reopening, usually within one to three freeze-thaw seasons. Structural crack repair requires assessment by a licensed structural or geotechnical engineer to determine the cause and whether the movement is ongoing or historic.

For historic buildings in Canada, the Standards and Guidelines distinguish between stabilization — stopping ongoing deterioration — and restoration, which involves returning fabric to a documented earlier state. Most practical masonry repair work falls under stabilization: arresting the deterioration process while retaining as much original material as possible.

The underlying principle, articulated consistently in Canadian heritage conservation literature, is that original material has irreplaceable heritage value. Restoration work should remove the minimum necessary to arrest deterioration and should use reversible or retreatable techniques wherever feasible. That principle distinguishes conservation-grade repair from ordinary commercial renovation work.