Should old Ottawa brick get lime mortar or Portland cement mortar?

For older brick in Ottawa, the choice between lime and Portland cement mortar depends on the wall. The Ontario Building Code (O. Reg. 163/24, 9.20.3.1.(1)) requires mortar to conform to CSA A179 and that lime used in mortar be hydrated; it sets no requirement about matching old mortar or using lime over Portland.

The guidance that does address historic brick comes from heritage district plans. The Centretown and Minto Park plan states that "lime-based mortar should be used when repointing historic brick and masonry as cement mortar prevents moisture from escaping through the mortar and causes brick damage," and that "care should be taken to match the colour and joint profile of the mortar." The Wilbrod/Laurier and Daly Avenue plans both state that "new mortar must match the original in colour, pointing method and composition (soft, lime rich mortar rather than a cement based mortar)." These are plan guidelines, not province-wide code rules, and they apply to those specific districts.

What a mason needs to assess before choosing a mortar:

• the age and condition of the existing brick
• what the original mortar was (colour, texture, composition)
• whether the wall is in a heritage conservation district or is individually designated
• the mortar type for the wall's exposure and load (the Building Code's Table 9.20.3.2.-A lists type N or S for exterior above-ground non-loadbearing walls and type S for loadbearing walls)

When getting quotes, ask each mason to specify the mortar type and mix they plan to use, how they will match the existing colour and joint profile, and how they will control silica dust when cutting out old joints. Ask for the mortar specification in writing as part of the quote, along with the joint profile, and the area to be repointed.

If the property is in a heritage district or is individually designated, the district plan or designation by-law may shape what mortar is acceptable; that is worth confirming before work begins.