A brick expansion joint must stay free to move

A brick expansion joint is a deliberate, continuous gap through a layer of brickwork, usually weather-sealed with flexible sealant. It divides the masonry into sections that can move without pressing against one another. It is not a mortar joint left unfinished—and filling it with mortar defeats its purpose. Brick Industry Association (BIA), Technical Note 18A

Before specifying or repairing one, establish the material and wall construction. The guidance below concerns fired-clay brick walls and veneers, not concrete bricks, thin-brick systems or refractory oven linings. An existing load-bearing wall needs a different assessment from a non-load-bearing brick facing.

Why brickwork needs room to move

Clay brickwork expands and contracts with temperature and generally undergoes long-term moisture expansion. Concrete masonry, by contrast, tends to shrink. If surrounding construction restrains these movements, stresses can build until the masonry cracks. A brick expansion joint can partially close as the brickwork grows. Brick Development Association (BDA), Designing for Movement in Brickwork

This explains three distinctions:

• Brick expansion joint: separates sections of brickwork and accommodates their movement.
• Concrete masonry control joint: creates a plane of weakness to locate shrinkage cracking; it tends to widen as the masonry shrinks.
• Building expansion joint: separates entire building sections, including the underlying structure—not just the brick facing.

These details are not interchangeable. A brick veneer and its concrete-block backing may need different movement-joint layouts. BIA Technical Note 18A

Where joints belong—and why spacing varies

Placement starts with the elevation, wall supports and expected movement, rather than a repeated distance alone. Designers consider corners and short returns, offsets, changes in wall height, material transitions, changes in backing or support, and window and door openings. Vertical joints generally continue to the top of the brickwork, including parapets. BIA Technical Note 18A

Published spacing recommendations differ by construction context. These are design guides, not a substitute for the project’s applicable standards and engineered layout:

Guidance	Published recommendation	Important qualification
U.S. BIA, May 2019	Brick veneer without openings: no more than 25 ft (7.6 m); with multiple openings: consider reduced spacing no more than 20 ft (6.1 m)	Width, compressibility, restraint and wall configuration also govern spacing; parapets need wider or additional joints when spacing exceeds 15 ft (4.6 m)
UK BDA, April 2023	General clay brickwork: approximately 10–12 m; unrestrained parapets and freestanding walls: 5–6 m	Corner distances, geometry, exposure and brick properties require consideration

Sources: BIA Technical Note 18A and BDA movement guide.

Joint spacing and width must be designed together. Neither guide provides a universal layout for every building. The BDA, for example, gives a 16 mm-wide joint at 12 m centres as a general allowance for movement and filler compressibility. BIA bases spacing on the expected movement and the compressibility of the least-compressible joint component.

Openings need particular care. Aligning a vertical joint with a window jamb may look tidy, but a loose-laid lintel requires detailing that permits its independent movement and checks the masonry load it carries. Joint placement must not undermine lintel support. BIA Technical Note 18A

Horizontal joints serve a different direction of movement. Where veneer is supported on shelf angles—the steel supports carrying the brickwork above—horizontal joints belong immediately below those angles. Brick infill also needs movement allowance between its top and the structural frame. These gaps must accommodate the relevant differential movement, not simply imitate an ordinary bed joint. BIA Technical Note 18A

What a working joint contains

A surface bead of sealant is only the weather seal. The movement gap behind it must remain functional.

1. An unobstructed gap through the brick layer. Mortar, debris and rigid reinforcement must not bridge it. Any connection crossing the joint needs a designed movement detail.
2. Highly compressible filler where specified. BIA describes full-depth foam or neoprene filler; ordinary fibreboard is insufficiently compressible.
3. A backer rod behind the sealant. This controls sealant depth and provides a tooling surface. The sealant must not bond to the rod, allowing it to deform between the two masonry faces.
4. Compatible elastomeric sealant. It must accommodate movement, withstand exposure and bond to the adjacent materials. BIA specifies ASTM C920, Grade NS, Use M, and recommends Class 50 or Class 100/50 sealants to minimise the number of joints. Colour alone is not a specification.

BIA recommends backer rod approximately 25% larger than the joint width and sealant depth approximately half the joint width, with a minimum depth of ¼ in. (6.4 mm). Confirm the selected sealant manufacturer’s requirements for joint dimensions, backing, primer and substrate preparation; BIA also recommends field adhesion testing before construction. BIA Technical Note 18A

Maintaining joints in existing walls

During periodic inspections, look for missing or torn sealant, loss of elasticity and separation from the masonry. Record photographs and associated damp staining. Failed sealant should be removed carefully, the joint cleaned, and suitable backing and compatible sealant installed—not covered with another bead over the failed material. BIA, Maintenance of Brick Masonry

Keep movement joints out of the mortar repointing scope. If one has been packed with mortar, restoring movement requires checking the obstruction and joint detail, not merely replacing its visible face. Repeated sealant failure warrants reviewing movement, dimensions and adhesion before repeating the same repair.

Adding a new joint is a separate intervention. BIA describes remedial cutting in some circumstances but stresses placement, alignment and structural integrity. Do not turn an unexplained crack into a saw-cut joint or cut through load-bearing masonry without a designed repair. BIA Technical Note 18A

For historic brickwork, do not treat the absence of modern expansion joints as an automatic reason to cut them in. Have the existing construction and movement assessed before removing sound fabric. The U.S. National Park Service rehabilitation standards favour retaining historic materials and construction features; the accompanying guidance recommends case-specific preservation advice. A proposal to add joints should identify their necessity, effect on support, weathering detail and impact on the historic bond—not just a spacing dimension.