04/05/2004

Exterior Brick Masonry Walls

Combating Deterioration of Masonry Building Envelope Systems

 

PHOTO: HOFFMANN

PHOTO: HOFFMANN

The High Points of Re-pointing Deteriorated Mortar Joints

Mortar joint deterioration is not only common, it’s inevitable. When the bond between bricks and mortar fails, it’s time to re-point. Re-pointing projects should not be undertaken in very cold, very hot, or very dry weather. Rather, brick surface temperatures should remain between 40 and 95 degrees F. during re-pointing. Proper re-pointing requires that care be taken in:

  • Removing old mortar to a depth of 5/8 of an inch (with a mason’s chisel or hand-held grinder in a manner that does not damage the brick).
  • Selecting replacement mortar material that is appropriate in color, texture, and flexibility.
  • Installing replacement mortar compactly in a joint that is dust-free and saturated/surface-dry.
  • Tooling the filled joint to achieve a concave surface that directs water off the face of the brick.

Aside from its visual appeal, brick (as an exterior building material) is durable. Over time, however, its deterioration is inevitable. Because bricks are porous – they expand or contract according to moisture levels and thermal influences – water is a constant threat and the principal cause of deterioration in brick at the building envelope. So is the restriction of movement in brick building envelope systems.

Types of Wall Construction

Brick exterior walls can be classified as either barrier walls or drainage walls. Barrier walls are constructed of solid masonry without drainage cavities. They can be constructed of single or multiple wythes, entirely of brick, or with concrete masonry unit or terra cotta back-up. Multiple wythe brick barrier walls (three wythes or more) are designed to prevent water infiltration to interior spaces through mass. Ideally, the amount of water absorbed by a wall over a given period of time is less than can be dissipated in the same time period. In a barrier wall constructed with two wythes of brick (or in composite walls), a collar joint (grouted solid with mortar) joins face brick with a masonry back-up. Water that penetrates the face brick follows the collar joint down to flashing where it is either expelled through the bed joint and/or at weeps, or it dissipates through the face of the wall.

Drainage walls are designed with cavities between outer wythes of face brick and back-up walls (brick, concrete masonry units, metal or wood stud framing). Ideally, water that penetrates the face brick or enters the cavity is collected at flashing where it is expelled through a bed joint and/or at weeps.

When Brick Exteriors Fail

Symptoms of deterioration in brick exterior walls are generally attributable to water infiltration and include staining and efflorescence, cracking/spalling/displacement, and deterioration in mortar joints, among other things.

Efflorescence occurs when water washes soluble salts out of mortar and onto the surface of brick. It is apparent in the form of white crystalline particles that develop on brick surfaces as water evaporates.

Cracks and spalls in brick can result when water absorbed/retained by brick freezes. The expansion of steel (embedded reinforcing or lintels) from rust in brick wall systems can also cause cracking/displacement.

Mortar, used to bond bricks together, must be softer than the brick it binds (so bricks don’t crack during expansion), and must be tooled in a way (concave/rodded) that discourages the collection of water in the joint. Re-pointing is required when the bond between the brick and the mortar fails.

The Roles of Relieving (Shelf) Angles and Soft Joints

Brick expands and contracts with changes in temperature and moisture content. Relieving (shelf) angles are necessary to ensure that movement is accommodated between face brick and back-up wall systems, and that cracks and displacement attributable to restraint in the system are alleviated. Soft joints installed at horizontal (shelf) angles, and at vertical control and expansion joints, will accommodate movement and create relief for the brick’s expansion.

Brick Masonry Walls that Endure

Properly design, install, and maintain flashings and weeps. Check those mortar joints. Provide adequately for movement within brick wall systems. Brick exterior wall systems designed and built to expel water and accommodate movement will endure.

Scott D. Chamberlain, project manager, North Haven, CT-based Hoffmann Architects (www.hoffmannarchitects.com), directs a variety of building envelope rehabilitation projects, including those for brick façades.

 

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Need portable cooling?

Rent or buy spot coolers from full-service locations nationwide. On call “24/7”. Primary, supplemental or emergency cooling. Atlas Sales & Rentals, Inc., or call (800) 972-6600.

Click here for more info


Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

Bluebeam® Revu® simplifies digital facilities document management from design review to leveraging as-builts, maintenance manuals and O&Ms submittals.

Yaskawa drives offer quality performance for air handlers and cooling towers on the roof to secondary chilled water pumps in the basement

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.


 
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