Masonry Terminology

What is repointing?
Repointing is the removal of old deteriorated/eroded mortar from between masonry units followed by the pointing of new mortar. The mortar is cut back to a depth twice the width of the mortar joint, then it’s cleaned out and misted before proper repointing can commence (preparation is paramount to achieve a quality product).

What does the term PSI mean?
-Psi is “pounds per square inch” and is a measure of the load bearing ability of the material in questions.

What is Portland cement?
-In Canada, there are six different types of Portland cement. Each mixture is designed to meet different chemical and structural requirements. The six types of cement are as follows:

  • Type GU – General Use Hydraulic Cement. This is the most common type of Portland Cement. The Vast majority of cement-based products are made using Type GU cement. This is the cement used in residential buildings.
  • Type MS – Moderate Sulphate Resistant Hydraulic Cement. It is often used in applications where the concrete will be exposed to sea water, or other sources of sulphates.
  • Type MH – Moderate Heat of Hydration Hydraulic Cement. This cement is used in large-scale applications where the heat that radiates from the concrete during the curing process may cause issues due to uneven heat distribution and pressure.
  • Type HE – High Early Strength Hydraulic Cement. This type of cement is similar to General Use cement, except for that it is ground into finer granules, allowing the concrete to cure faster. This is helpful when a structure needs to be put to use within a short period of time after being built, or during cold weather construction when the cold will adversely affect a long-cure cement.
  • Type LH – Low Heat of Hydration Hydraulic Cement. This type of cement is much like Type MH, but with a lower heat value. This cement takes a much longer time to cure, and is only used on incredibly large scale applications such as dams.
  • Type HS – High Sulphate Resistant Hydraulic Cement. Much like Type MS, only with a greater resistance to the adverse affects of sulphates. This cement is used where it will be in contact with very sulphate-rich ground waters and soils.
  • White Portland Cement. Types GU, and HE cements are available as a white cement. The whiteness is caused by limiting the amounts of iron and magnesium-oxides present in the cement mixture. White cements are used primarily based on architectural design where a lighter concrete colour is desired.

What is Lime?
-Masonry Lime is a very fine powder that is made by firing limestone in a kiln, and then crushing it. When lime powder is added to a cement-based mortar, it creates a softer, more workable product. Lime also allows mortars to become more flexible, breathable, and absorbent.

I’ve heard of additives used in mortar. What are they and what do they do?
-Additives are chemical compounds that are used in conjunction with the water in mortars. There are different additives designed for different purposes. Some speed up the curing process, while others slow it down. There are also adhesive additives that allow new concrete to better stick to old foundations and plasticizers that allow concrete to flow better.

What is the difference between a course of bricks and a wythe of bricks?
-Courses of brick are the horizontal rows of bricks, blocks, or stones that make up a masonry wall. A wythe is a continuous vertical section of brick, block or stone in a load bearing masonry wall. Most homes in Ottawa are constructed with wood, and only have a single wythe of masonry protecting them from the elements (this is then referred to as a veneer), but in many older areas around the Ottawa region it is not uncommon to find double, and even triple wythe structural masonry walls.

What is the difference between cement and concrete?
-Concrete is a very strong material created by bonding fine and coarse aggregates together. Cement is the material that bonds these aggregates together. While mortar contains portland cement, lime, and sand, concrete contains all of these ingredients (minus lime) as well as larger stones (gravel, or aggregate). Concrete is often mistakenly referred to as cement.

What is parging?
-Parging is a protective layer of cement that coats the outside of the exposed foundation. This parging layer is exposed to the elements rather than the foundation itself. This way most exterior damage is inflicted on the parging, leaving your actual foundation in good condition. Much like mortar, the parging layer is sacrificial and intended to become damaged over time and repaired when necessary.

What is a weeping hole?
-A weeping hole is a space left between bricks along the top and bottoms of window and door openings, as well as the wall itself. Weeping holes are generally spaced apart every three or four bricks. They allow any water that finds its way into the wall to escape back out, preventing water damage. Another benefit of weeping holes is the ability to allow pressure stabilization between the wall cavity and the outside atmosphere. Without this stabilization, any low pressure within the wall can actually pull water and pollutants into the wall at an accelerated rate, speeding up the rate of deterioration. Some older homes don’t have weep holes.

What is a control joint?
-Control joints are planned vertical wall separations, which divides the wall into sections. These are used to accommodate thermal changes that occur within the masonry as seasons progress. The masonry expands and contracts as it warms and cools causing a lot of stress on the wall. Typical areas you find control joints are at certain wall heights and lengths, thickness changes, adjacent foundations, near corners and intersecting walls, or near doors and windows where proper reinforcement is not provided.