Weatherproofing

The enduring strength, beauty and performance of a brick wall assembly is critically dependant on three components: design, workmanship and materials. If even one of these factors has not been diligently applied, integrity of the wall assembly is compromised.

The single most important factor to be understood and designed for in the severe northern climate is moisture control. Seldom does failure of brick wall assembly occur without the presence of an excessive moisture load. Excessive is defined as being more moisture than can dry out of the assembly before that assembly freezes due to ambient temperature conditions. The trapped moisture will freeze and thaw and may cause deterioration known as spalling, in which part of the brick surface may break away.

Examples of Extra Severe Weathering Conditions

• Houses and buildings built within the spray zone of lakes
• Buildings constructed in open areas, with little or no protection from the wind by other buildings or trees
• Upper floors of high rise buildings

It should be noted that certain parts of masonry structures are more vulnerable to the weather than others. These include surmounting multi-story buildings, freestanding walls, chimneys and walls put in contact with the garden grade level. In parapet walls, these adverse conditions, it is even more critical to ensure the correct use of materials, details and workmanship.

Chimneys
The two most critical components of chimney construction are workmanship and a proper chimney cap. (See Fig. A for proper chimney cap details) Ensure that the chimney can installed has an overhang of no less than 50mm (2"), and a drip groove (as shown in Fig. A) to shed water past the plane of the four chimney wall. Ensure that all joints are properly caulked.

Note: The through wall flashing detail shown in Fig. A applies to all masonry walls which traverse the roof line. I. E. where an exterior wall (or chimney) above the roofline is supported below the roofline by masonry, through wall flashing must be installed at the roofline to direct water to the exterior.

Window Sills
Important details for window sills:

• Minimize the number of joints
• Ensure minimum slope of 15" to sill
• Provide drip groove
• Provide adequate flashing including end dams
• Caulk all joints

The most fail-safe detail is to choose a stone, concrete or metal sill material that is tailored to the window opening and has a slope on top and a drip groove/tip on the under side. (See Fig. B)

Brick at Grade
Brick built on grade can result in the ingress of moisture, either from direct water run-off or the build-up of snow. Excess moisture present in the brick during the freeze-thaw cycles can result in spalling of the brick.

Good building practice dictates that brickwork should be a minimum of 150mm (6") above grade.

This requirement also applies to any level surface such as paving, patio deck or balcony. Furthermore, the ground should be contoured so that the water drains away from the wall. (See Fig. C)

Base flashing should be installed below thebottom course of masonry to prevent the upward migration of moisture due to capillary action (rising damp). Always slope the grade away from the building. The masonry wall assembly should begin no less than 150mm (6") above the grade line.

Grade should be measured from the top of the finished surface. This means that grade should be considered to be the top of a wooden deck, a stair tread, a poured concrete balcony, or any sort of finished surface, be it paving brick, gravel, asphalt, or the earth in a planting bed.

Weepholes - Brick Veneer Walls
Brick veneer walls, if correctly installed, provide the best protection from rain penetration. However, often critical details are omitted, causing the wall to become ineffective, and water to penetrate past the wall. Two of the details often omitted are weepholes and flashing. (See Fig. C)

This detail should be at the base of all brick veneer walls, on top of windows, doors and other
openings into brick veneer walls.

Parapet Walls and Columns
The top of parapet walls, freestanding walls and columns are subjected to the same severe weathering as chimneys. Hence, they also require special attention to details. (See Fig. D) shows a typical cap for a wall or column. A stone or precast concrete cap with an overhang and drip groove is recommended.

The minimum overhang should be 50mm (2") with the placement of the drip groove 25mm (1") from the masonry wall.

Retaining Walls, Etc...
Brick walls used to retain soil, in planters, or other applications will be subjected to moisture ingress from the soil. The brick wall should be constructed with a concrete block backup wall with a cavity, (airspace), base flashing and weepholes to permit moisture to drain away from the masonry.

The interior side of the concrete block backup should be coated with a waterproof material to
prevent moisture transmission through the wall. (See Fig. E) Drainage should be provided at the base of the planter box to prevent the build up of hydraulic pressure.

Roofing Details - Overhang
Buildings should be designed with adequate roof overhang to reduce the exposure of the wall to weathering. (See Fig. F)

Research shows that even a modest roof overhang significantly reduces the amount of water reaching the wall.

Eaves trough (gutters) and downpipes should be correctly sized and positioned to remove rainwater without undue overflow onto the walls.

Caulking and Sealants
caulking of joints is critical to prevent the ingress of moisture, however, with time and weathering, elastomeric caulking materials will deteriorate and become ineffective. Caulking materials should be inspected regularly and replaced when necessary.

Water Repellent & Colorless Coatings
The Brick Institute of America (BIA) warns that in climates that experience freeze-thaw cycling, colorless coatings may adversely affect the durability of brick masonry by inhibiting moisture evaporation. The use of masonry water repellents is suggested sometimes as a possible solution to leaky walls. Before these products are considered, construction details need to be checked for integrity.

Items contributing to leakage include ineffective flashing at the base of the wall, absence of a clear cavity and weepholes, unfilled head joints or cracks at the mortar/brick interface. Air leakage from the interior can be a major cause of moisture on the inside of the brick veneer.

Gas Furnace Outlet
The vents from gas furnaces and other appliances should be directed to discharge moisten laden air away from the masonry.

Workmanship
Beside the use of correct materials and proper design details, good workmanship is required to ensure successful performance of masonry.

Joint Profiles
The tooling and profile of a mortar joint has a significant effect on the ability of the mason to resist moisture penetration. (See Fig. G for different joint profiles)

Rake joints are popular because they accent the aesthetics of the brick.

However, they are not recommended for exterior masonry work in the severe northern climate. Raked joints provide a ledge for moisture ingress and retention.

Concave tooled joints are recommended for all exterior masonry. Joints should be tooled when the mortar is thumbprint hard. The jointing tool should be larger than the joint width; i. e. Use a 12mm (1/2”) diameter tool for a 10mm (3/8”) joint width. The tooling process smooths and compresses the joint to promote superio water repellence.

Summary
If moisture entry and retention in the brickwork is avoided by the application of well considered design, quality workmanship and the correct choice of component materials, the enduring strength, beauty and performance of your masonry wall assembly should always be a source of pride to you.

Please consider the information listed in these technical notes as advisory highlights only. There are certainly many more conditions to be considered in the design and construction of a masonry wall assembly in a severe weatherclimate zone, such as the northern region. Those considerations are best left to your design and construction professionals.