Brick ties, sometimes called ‘brick anchors’, are metal strips or bars used to connect the two leaves of a cavity wall. This allows the inner and outer parts of the wall to act together as one solid structure.
Although hidden from view after construction, brick ties play a vital role in reinforcing cavity wall buildings. Insufficient or incorrectly installed ties can lead to severe issues like damp penetration, cracks, or even collapse of the outer leaf.
Key Takeaway: Brick ties connect the two leaves of a cavity wall, providing crucial structural stability.
How Brick Ties Connect Cavity Walls
Cavity walls have been the standard construction method in the UK and many other countries since the early 1900s. This involves two “skins” or rows of bricks with a gap or cavity between them.
Brick ties span this cavity, embedding into the mortar bed of each leaf. This binds the inner and outer wall together into one cohesive unit that can resist lateral forces like wind or earthquakes.
Without the connecting ties, the separate leaves would act independently. The outer leaf could detach or bulge outwards due to wind load or foundation issues. Brick ties transfer stresses between the leaves, maintaining structural integrity.
Materials and Corrosion Resistance
Brick ties must be corrosion resistant, as moisture is present within the wall cavity. Galvanized steel ties were historically common but can corrode within 15-20 years.
Modern ties are predominantly stainless steel, which is not affected by water or cement. Stainless steel ties offer a maintenance-free lifespan and minimize material use.
Some composite materials are also used, like basalt fiber ties in low-energy buildings. Their low thermal conductivity helps reduce heat loss through the cavity.
Installation of Brick Ties
During construction, brick ties are built into the wall as it progresses:
- Press the brick tie into the fresh mortar bed of the inner leaf.
- Ensure the tie is surrounded by mortar to prevent air gaps.
- Position the drip part of the tie near the cavity center, angled slightly downwards.
- Repeat this process with the outer leaf, fully embedding both ends of the tie.
For non-standard builds like thin joint blockwork or timber frame, ties are often installed after the inner leaf is complete:
- Attach one end of the brick tie to the inner leaf or frame with screws.
- Embed the outer end in the fresh mortar of the outer leaf as it is built.
Brick Tie Length and Cavity Widths
Brick ties must span the full cavity and have a minimum embedment of 62-75mm in the mortar on both sides.
Tie length depends on the cavity width:
- 50-75mm cavities need 200mm ties
- 76-100mm cavities need 225mm ties
- 175mm cavities need 300mm ties
- Over 175mm, calculate the tie length as the cavity width plus 125mm
Symmetrical ties allow for on-site variability in cavity width or tie centering. If the cavity differs significantly from the tie length, longer ties are required.
Spacing and Density of Brick Ties
According to building standards, cavity walls require:
- Minimum of 2.5 brick ties per square meter of wall
- Maximum horizontal spacing of 900mm between ties
- Maximum vertical spacing of 450mm between courses
This equates to one tie per 600mm x 450mm in a staggered layout.
Around openings, unbonded edges, and movement joints, the vertical spacing decreases to 300mm (or 225mm maximum from openings).
More ties concentrated in vulnerable areas help maintain stability. The quantity and layout ensures an even distribution tying the full wall surface.
Selecting the Correct Brick Tie
Choosing suitable brick ties depends on:
- Cavity width
- Masonry materials and thickness
- Building height and dimensions
- Wind/seismic conditions based on geography
In the UK, Ancon’s PD 6697:2010 guidelines aid selection based on location. Four tie types suit most standard masonry cavity builds:
| Type | Application | Density | Max Height | Location |
|---|---|---|---|---|
| Type 1 | Heavy duty, all building types | 2.5/m2, 3-4 at edges | Any | All regions |
| Type 2 | General, small buildings | As Type 1 | 15m | Wind ≤ 31m/s, altitude ≤ 150m |
| Type 3 | Basic, as Type 2 | As Type 1 | 15m | Wind ≤ 27m/s, altitude ≤ 150m |
| Type 4 | Light duty, domestic | As Type 1 | 10m | Urban, wind ≤ 27m/s, altitude ≤ 150m |
Other specialty ties are made for wider cavities, steel frames, timber frame, thin joints, etc. Always follow standards to select suitable brick ties.
Identifying Brick Tie Failure
It can be difficult to detect brick tie issues, but warning signs include:
- Horizontal cracking in the outer leaf at regular intervals
- Bulging, distortion, or detachment of the outer leaf
- Cracks around openings like windows
- Sagging or lifted lintels
This often results from corroded, expanded ties applying outward pressure. A professional survey is recommended to inspect for deteriorated ties needing replacement.
Conclusion
Brick ties are a small but vital component in cavity wall construction. By binding the inner and outer leaves together, they allow the wall to act as one solid structure resistant to lateral and out-of-plane loads. Correct selection, spacing, and installation of suitable corrosion-resistant ties prevents long-term issues like cracking, bowing walls, and even structural failure. Specifiers should always follow building standards to ensure appropriate tie provision for durability.
Frequently Asked Questions
What are brick ties made of?
Modern brick ties are usually stainless steel for corrosion resistance. Galvanized steel ties were previously common but can corrode. Some fiber-reinforced plastic ties are also used.
Where are brick ties placed in the wall?
Brick ties are embedded in the horizontal mortar joints, spanning the cavity to tie the two leaves together. The ends should have a minimum embedment of 62-75mm into each leaf.
How many brick ties are needed per m2?
Building standards specify a minimum density of 2.5 ties per m2 of wall area. They are typically spaced at maximum intervals of 900mm horizontally x 450mm vertically.
How can you tell if brick ties are failing?
Signs of failure include horizontal cracking of the outer leaf, bulging/leaning walls, cracks around openings, and sagging lintels as corroded ties expand. A professional survey is recommended to inspect for deteriorated ties.
What happens if there are insufficient brick ties?
Insufficient ties lead to reduced structural integrity as the leaves act independently. This can result in cracking, moisture penetration, and potentially collapse of the weaker outer leaf under wind or out-of-plane loads.