The Regulatory Context for Heritage Repointing
In Canada, repointing work on a designated heritage property is typically subject to approval from the local heritage authority—a municipal heritage committee, provincial heritage branch, or, for federally owned buildings, Parks Canada. The threshold for what triggers a permit varies by jurisdiction. In Ontario, for example, the Ontario Heritage Act requires a heritage permit for alterations that affect the heritage attributes identified in a property's designation bylaw. Repointing the primary street façade of a designated commercial building will almost always fall within that definition.
The consequence of proceeding without a permit—or with a non-approved mortar— can include orders to restore the original condition at the owner's expense. Regulatory compliance is therefore a practical concern, not merely an administrative one.
Raking Out Deteriorated Mortar
Proper preparation is the step most commonly done incorrectly. The standard recommendation—repeated in Parks Canada's guidelines, the US National Park Service's Preservation Brief 2, and most provincial heritage documents—is to rake joints to a minimum depth of 19 to 25 mm (¾ to 1 inch) before applying new mortar. Shallower preparation produces a thin "cap" that lacks the mechanical bond necessary for long-term adhesion and is likely to fall out within a few freeze-thaw seasons.
Tools matter. An oscillating multi-tool with a carbide blade or a thin hand chisel and hammer are preferred for soft historic mortars. Angle grinders are consistently discouraged in heritage guidance because they cannot be controlled accurately enough at the joint edges and frequently nick or cut into brick arrises, creating water collection points and reducing the bearing area.
Where hand tools cannot achieve adequate depth without risk to the brick— as sometimes occurs where historic mortar has carbonated to exceptional hardness—a 4 mm diamond blade on a grinder may be used for a single centre cut, with the remaining mortar removed by chisel. This is a recognised exception, not a standard approach.
Joint Profiles in Heritage Contexts
The profile of the finished joint affects both drainage and appearance. The principal profiles used in historic commercial construction were:
| Profile | Description | Drainage Behaviour |
|---|---|---|
| Flush | Mortar level with brick face; tooled flat | Neutral; depends on mortar permeability |
| Slightly raked | Set 3–5 mm back from face; common in commercial work | Can collect water if raked too deeply |
| Weathered (struck) | Angled to shed water; upper edge flush, lower edge recessed | Good drainage; historically common in exposed walls |
| Rodded (concave) | Curved inward; produced with a round-bar tool | Good drainage; often applied in 20th-century repair work |
Heritage guidelines generally require that the repair joint profile match the original. A deeply raked or extruded profile on a wall that was originally flush-tooled is unlikely to receive approval from a heritage officer and changes the visual character of the façade in ways that may be difficult to reverse.
Mortar Colour and Texture Matching
New mortar will appear lighter than weathered joints immediately after application and will darken somewhat as it cures and carbonates. A colour assessment should be made at the same curing stage as the existing mortar, not immediately after application. Mock-up panels—small test areas applied and allowed to cure before the full repointing proceeds—are standard practice on significant heritage projects and are often required by heritage authorities as a condition of permit.
Colour adjustment is primarily achieved through aggregate selection (see the mortar analysis article). Pigments can be used but should be used conservatively; excessive pigment can affect the mortar's physical properties.
Application and Curing
New mortar should be applied in layers no thicker than 10 mm (⅜ inch) when filling deep joints. Each layer should be allowed to firm up—typically 24 hours in normal conditions—before the next is applied. The final layer is tooled to the correct profile when the mortar is "thumbprint hard": firm enough to retain the tool impression without smearing.
Curing protection is important in Canadian conditions. Freshly repointed masonry should not be allowed to freeze for at least 72 hours after application, and should be protected from direct sun and wind in hot weather to prevent rapid drying. Lime mortars in particular benefit from slow, moist curing and may be kept damp with a fine mist or damp burlap for the first 24 to 48 hours.
Seasonal Restrictions
Repointing in temperatures below 5°C (41°F) requires cold-weather protection measures including heated enclosures and anti-freeze admixtures compatible with the mortar type. Most provincial heritage authorities and standard masonry specifications recommend avoiding repointing when ambient temperature is below 5°C and falling. Work above 32°C (90°F) or in direct summer sun requires shade and accelerated curing control.
References
- Parks Canada. Standards and Guidelines for the Conservation of Historic Places in Canada, 2nd ed. Ottawa, 2010.
- Ontario Ministry of Heritage, Sport, Tourism and Culture Industries. Ontario Heritage Act, R.S.O. 1990, c. O.18.
- National Park Service (US). Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings.
- Masonry Standards Joint Committee. Building Code Requirements for Masonry Structures (TMS 402).