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Mortar Questions

What is mortar?
-Mortar is a workable material, used as a binding and leveling agent between various masonry units. Mortar is comprised of various ratios of fine sand, Portland cement, lime, and water depending on application.

What do different ratios of Portland and lime do to the mortar?
-Mortar types are organized by their composition, and labelled using a lettering system. In order of strength, the mortar types are Type M, Type S, Type N, Type O, and Type K. The most common types are S, and N.

  • Type M mortar is the strongest of these mortar types. It consists of 3 parts cement, 1 part lime, and 12 parts sand. It has a very high compressive strength at 2,500 PSI. It is most commonly used for stone jobs, and foundations.
  • Type S mortar is made up of 2 parts cement, 1 part lime, and 9 parts sand. Due to its higher lime content, Type S mortar is more flexible, yet still strong having a compressive strength around 1800 PSI. Thanks to this flexibility, Type S mortar is used in above-grade foundation work, retaining walls, and paving situations.
  • Type N mortar is the mortar that is most commonly used in the construction of brick walls. It has a lower PSI at about 750 and a good amount of flexibility due to its lime content. It is made up of 1 part cement, 1 part lime, and 6 parts sand.
  • Type O mortar is made up of 1 part cement, 2 parts lime, and nine parts sand. This makes it even softer than Type N around 350 PSI. It is used primarily for repointing non-loadbearing walls.
  • The final mortar type is Type K. It is exclusively used on heritage buildings. The bricks used a hundred years ago are much softer than the bricks used today, and therefore need a mortar even softer than that, around 75 PSI. It is made up of 1 part cement, 3 parts lime, and 10 parts sand.

I have coloured mortar. Can you match it?
-Yes, we carry a selection of mortar pigments with us to every job, and have become quite proficient in matching mortar colours.

I’ve seen many different finishes on mortar joints, does one have an advantage over others?
-There are many different types of mortar joints, but the main ones you would encounter on a typical residential home are flush, raked, and concave (aka jointed). Often you’ll hear different names used, but a description of each will follow. There are numerous other finishes for different architectural purposes and also offer varying degrees of weather resistance. A flush finish is when the masonry joint is brought flush with the brick or masonry unit and is generally used if the masonry is to be painted to give walls a more uniform look. Raked joints are another finish where the mortar joint is recessed about 3/8th of an inch having each brick stand out more compared to the uniformity of a flush or concave finish. Raked finishes are generally the most aesthetically appealing. A concave finish is the most common mortar joint as it produces the best weather protection.

The mortar between my bricks is soft, and seems to erode easily. Why wasn’t a stronger mortar used?
-There was a time when it was “stronger” but it has just weakened over time. A common problem when it comes to repointing is that people assume stronger mortar means stronger walls. Mortar must be weaker than the units themselves or when the freeze/thaw cycles occur during the spring and fall seasons breaking and spalling of the units will occur. This is caused by the different composition of mortar, clay bricks, concrete blocks, and stones, as they expand and contract at different rates. Mortar joints are sacrificial to the units they surround and mortar is much easier to repoint than bricks, blocks, and stones are to replace.

There is mortar missing between some bricks in my wall. Can you fill these gaps in for me?
-We are fully capable of repointing any deteriorated mortar joints that may occur on your home, although, there are some joints that are left intentionally empty. These joints most often occur above and below window or door openings, and at the base of masonry walls. They are known as ‘weeping holes,’ and they allow water that has found its way into the wall to escape. Without these intermittent gaps in the wall, trapped water would collect and pool behind the bricks, causing water damage to both the masonry wall, and the structural elements of the home.