The right mortar for repointing depends on what you’re matching: use Type N or Type S (Portland-based) mortar for standard modern brick, and use a natural hydraulic lime (NHL) or lime-based mortar for older brick, fieldstone, or sandstone, especially on homes built before the 1930s. The goal is always to match the mortar’s hardness and breathability to the material you’re repairing, never make it harder than what it’s holding together.
Why This Matters More Than People Think
A lot of repointing problems don’t come from bad workmanship; they come from the wrong mortar mix. If the mortar is harder and less permeable than the brick or stone around it, moisture that gets into the wall has nowhere to go. Instead of the mortar joint managing that moisture the way it’s supposed to, water gets pushed out through the brick or stone face instead, and in a cold climate like Calgary’s, that moisture freezes, expands, and cracks the material itself. At that point, you’re not looking at a simple repoint anymore; you’re looking at brick or stone replacement, which costs a lot more and is a lot harder to match.
Portland-Based Mortar (Type N, S, O, M)
These are the standard mortars used on most brick buildings from roughly the 1930s onward, when brick manufacturing shifted to harder, denser, machine-pressed units.
- Type N – General-purpose mix, moderate strength, the default choice for most above-grade residential repointing on standard brick.
- Type S – Higher strength, used for load-bearing work, below-grade applications, or areas exposed to higher structural stress.
- Type O – Softer, lower strength, sometimes used on very soft historic brick where even Type N would be too hard.
- Type M – Highest strength, mainly for heavy structural or below-grade masonry, rarely the right call for standard home repointing.
For most Calgary homes with standard modern brick, we typically spec Type S for exterior joints. It balances compressive strength with enough flexibility to handle Alberta’s temperature swings better than a straight Type N mix in most cases. That said, the right type still depends on the specific brick and exposure, which is why assessing the material directly before quoting matters more than defaulting to one type across the board.
When to Use NHL or Lime Mortar Instead
If your home was built before the 1930s, or if you’re working with fieldstone, sandstone, or soft historic brick, Portland-based mortar is often the wrong choice, even the softer Type O. Older masonry materials are typically more porous, and they were originally built with lime mortar, which allows moisture to pass through and evaporate rather than trapping it.
Natural hydraulic lime (NHL) mortars come in different strength grades, commonly NHL 2, NHL 3.5, and NHL 5, corresponding to increasing hardness. The right grade depends on how soft or hard the original material is: softer, older sandstone or historic brick generally calls for NHL 2 or 3.5, while harder stone can sometimes tolerate NHL 5. When in doubt, it’s safer to go softer rather than harder; a too-hard mortar risks damaging the material around it, while a too-soft mortar just means you repoint again sooner, a far cheaper mistake to make.
Fieldstone vs. Brick: Does It Change the Answer?
Yes, but not always in the way people expect. Dense fieldstone (granite, some harder sandstones) is often less porous than old brick, so the mortar joint itself becomes the primary path for moisture to escape the wall. In that case, a mortar that’s too hard doesn’t necessarily crack the stone, but it can still cause the mortar itself to spall or pop out as water pressure builds behind it and finds the weakest point. Softer, more porous fieldstone behaves more like old brick, and needs a mortar that matches that permeability directly.
Why This Matters More in Alberta Specifically
Calgary and the surrounding area go through some of the most aggressive freeze-thaw cycling in the country, sometimes swinging above and below freezing multiple times in a single week during shoulder seasons. That cycling is exactly what turns a minor moisture-trapping problem into cracked brick or spalled stone within just a few years. Getting the mortar type right isn’t a historical-preservation nicety here, it’s a practical requirement for making a repair actually last through an Alberta winter.
Getting a Second Opinion
If you’re not sure whether your home needs Portland-based mortar or a lime/NHL mix, the safest step is to have someone experienced look at the actual material before you order anything. The age of the house is a strong clue, but not a guarantee, renovations and previous repairs sometimes mean a mix of materials on the same wall. Astrit Martinaj has been repairing Calgary brick and stone for over 20 years, and getting this one decision right from the start is what determines whether a repointing job lasts five years or fifty.