A crack above a window or beside a steel beam does not always begin with settlement or excessive loading. Sometimes, the force comes from the steel itself as it corrodes. Expanding rust can push against surrounding materials, split masonry, break concrete, and force steel connection plates apart.
This process, commonly called rust jacking, can affect both residential and industrial buildings. Its significance extends beyond the visible damage: corrosion can weaken the connections, supports, and interfaces that transfer loads through a structure.
Evaluating rust jacking brings together structural assessment, forensic investigation, and steel connection engineering. The objective is to understand the damage mechanism, determine the remaining capacity, and develop a repair that restores reliable structural performance. That approach is especially relevant to the rehabilitation and continued use of existing buildings and industrial facilities.
What Is Rust Jacking?
When steel corrodes, the resulting corrosion products occupy more volume than the steel consumed. If the rust is confined, its accumulation can exert pressure on adjacent materials. The resulting movement and damage are known as rust jacking.
At overlapping steel surfaces, the buildup is often called pack rust. Moisture enters a narrow gap, corrosion develops, and layers of rust gradually force the components apart. FHWA guidance on pack rust identifies plate distortion, weld cracking, and overstressed bolts as possible consequences of pack rust.
Corrosion affects a structure in two related ways: it removes sound steel, and its expansive products can damage the surrounding assembly. A thick layer of rust does not represent useful structural material or remaining capacity.
How Much Can Rust Expand?
Research on rust expansion in reinforced concrete describes corrosion-product volumes of approximately 2 to 6 times the volume of the iron or steel consumed. The Brick Industry Association's guidance on movement in masonry cites volumes up to 10 times the original steel volume.
The ratio varies with the corrosion products and their physical condition. It refers to the steel actually consumed by corrosion, not the original volume of the entire beam or lintel. For example, 1 cm³ of steel converted to corrosion products could produce approximately 2 to 6 cm³ of rust within the commonly cited range.
That expansion does not translate directly into the same increase in a component's dimensions. Some rust can occupy pores and gaps or escape through cracks. Pressure develops when surrounding materials restrain the accumulating corrosion products.
How Much Force Can Rust Jacking Exert?
There is no single rust-jacking pressure that applies to every building. The pressure depends on confinement, the properties of the rust, the surrounding material, and the space available for expansion. Cracking and movement can release part of that pressure.
For scale, a Colorado Department of Transportation research report on corrosion-induced deterioration calculated concrete cracking pressures of approximately 6.12 MPa and 9.60 MPa for its selected non-uniform and uniform reinforcement-corrosion scenarios. These are model-specific cracking pressures, not universal maximum pressures or design values for lintels and steel connections.
Pressure becomes force when it acts over an area. As a simple illustration, a uniform pressure of 6 MPa acting on a flat area measuring 100 mm by 100 mm produces a separating force of 60 kN, equivalent to the weight of approximately 6 tonnes. This calculation illustrates the scale of the force; it does not predict the pressure distribution in a particular connection.
Confined corrosion can generate enough force to split surrounding materials or distort steel connection components. The resulting damage depends on which part of the assembly cracks, bends, or loses restraint first.
Rusting Lintels and Cracks in Brick Veneer
Steel angle lintels commonly support brick veneer above windows and doors. When water reaches inadequately protected steel, corrosion can develop along surfaces concealed by the brickwork. Flashing and weep holes help direct water out of the wall, while appropriate corrosion protection helps protect the lintel.
Rust accumulating between a lintel and the surrounding masonry can lift or displace the brickwork and open mortar joints. Possible symptoms include cracking near the lintel ends, separation above the opening, and local brick damage. Corrosion of steel confined within masonry is a recognized cause of cracking and spalling.
Crack patterns alone do not establish the cause. Lintel deflection, restrained masonry movement, and foundation movement can produce similar symptoms. An assessment should consider the lintel, its bearing, the surrounding masonry, and evidence of moisture entry.
Brick veneer generally does not support the building's floors or roof, but it still requires reliable support and lateral restraint. Damage to its supporting lintel can become a falling-masonry hazard even when the main building frame remains unaffected. Repointing the visible cracks will not resolve continuing corrosion or restore a weakened lintel.
Steel Beams and Cracking at Their Supports
Steel beams bearing in masonry pockets or enclosed in concrete deserve particular attention when moisture is present. Applying the same corrosion-expansion mechanism, rust accumulating around a confined beam end or bearing plate can press against the surrounding material and cause splitting or local spalling.
For example, a beam end in a persistently damp wall pocket may develop concealed corrosion. Cracks beside the pocket could reflect pressure from rust expansion, deterioration of the bearing material, or another structural movement. The exposed length of the beam may appear relatively sound while its concealed end requires repair.
These cracks can have structural significance if they affect masonry or concrete transferring the beam reaction into the wall or foundation. The assessment must consider both the remaining steel and the condition of its support.
Rust on an exposed beam does not automatically mean that the beam itself will crack from expansion. Cracking of surrounding masonry or concrete is a different mechanism from cracking within steel or welds. In steel assemblies, confined rust between attached components can create forces that distort plates and distress connections.
Rust jacking of the steel beam caused stepped cracking in the wall above. The close-up shows heavy corrosion and layered rust buildup along the beam.
Industrial Connections: Rust Between Plates
Industrial buildings contain many interfaces where moisture can become trapped: beam splices, bolted brackets, built-up members, and connections supporting platforms or equipment. These are practical locations to investigate when applying the documented pack-rust mechanism to building structures.
As corrosion products accumulate between contacting surfaces, they can force plates apart and change the connection's geometry. Combined with section loss, this can affect its ability to transfer load. A connection that still has all its bolts in place may nevertheless require assessment if plates are separating, welds are cracked, or substantial corrosion is present.
Painting the accessible exterior does not establish the condition of concealed surfaces. The extent of corrosion and the remaining connection capacity need to be understood before a repair is selected. A structural connection assessment can establish whether repair, reinforcement, or replacement is needed.
Other Examples in Residential and Industrial Buildings
Reinforced Concrete Balconies, Garage Slabs, and Loading Docks
Corrosion of reinforcing steel can produce the same expansive effect inside concrete. Pressure from the corrosion products can cause cracks along the reinforcement, separation of the concrete cover, and eventual spalling. Research on corrosion-induced cracking and reinforcement bond also documents how corrosion can affect the interaction between steel and concrete.
In balconies, suspended garage slabs, and industrial loading docks, the structural concern can extend beyond loose concrete. Reinforcement section loss and impaired bond or anchorage may affect load transfer. A surface patch alone cannot establish that the reinforcing system remains adequate.
Shelf Angles, Wall Ties, and Embedded Anchors
Lintels are not the only concealed steel components in masonry. Shelf angles, wall ties, and anchors can also corrode. Expanding corrosion products can damage adjacent masonry, while loss of steel can weaken the support or restraint the component provides.
The consequence depends on the component's role. A shelf angle carries masonry weight; wall ties help restrain the veneer against lateral movement. Similar-looking corrosion can affect different parts of the wall's load path.
Column Bases and Equipment Supports
Another application of the confined-corrosion mechanism is steel at concrete or grout interfaces, including column bases and equipment supports. Where corrosion develops in a confined location, the assessment should consider possible damage to surrounding concrete or grout, as well as loss of steel in the plate or anchors.
Cracked grout at a base plate does not, by itself, prove rust jacking. Loading, installation defects, and other deterioration mechanisms also need consideration. The engineering question is whether the assembly still provides the intended bearing, anchorage, and restraint.
Why the Load Path Matters
A rust-jacking assessment should follow the affected structural load path. What does the damaged component support? Where does its load go next? Has corrosion affected the member, its connection, its bearing, or several of these at once?
For a window lintel, the concern may be local masonry support. For a beam pocket, it may be the transfer of floor loads into a wall. For an industrial bracket, it may be the connection carrying an operating piece of equipment. The visible size of a rust stain does not answer those questions.
Consider an industrial platform supported by a steel bracket attached to an existing column. Corrosion between the bracket and a connection plate may affect the bolts, the plate, and the bearing between components. Restoring the bracket alone may leave a weakened attachment or column component in the load path. This illustrative example shows why the assessment needs to follow the forces through the full connection and into the supporting structure.
From Forensic Investigation to Structural Rehabilitation
Accumulated rust, displaced masonry, recurring cracks, and movement out of the wall plane are reasons to investigate rather than repeatedly repair the finish. The Brick Industry Association's maintenance guidance identifies these types of conditions as potential indicators of structural concerns.
A forensic structural investigation focuses on identifying the cause of the damage. Depending on the assembly, it may require targeted openings, cleaning selected areas for examination, steel thickness measurements, and review of the loads and connections. Concealed deterioration cannot always be assessed from an exterior photograph or a visual inspection alone.
The investigation should distinguish damage caused by corrosion expansion from damage caused by section loss, excessive loading, movement, or deficiencies in the original detail. More than one mechanism may be present. Establishing the cause helps define what the repair must achieve.
Assessing Remaining Capacity and Connection Behaviour
For steel framing, the engineering review should consider the measured condition of the member and its connections, together with the loads they carry. Depending on the detail, relevant checks may include the remaining plate thickness, bolt and weld condition, bearing, local bending, and the effect of distortion on force transfer.
Where geometry or force distribution is complex, advanced structural analysis, including finite element modelling where appropriate, can help evaluate local behaviour and compare reinforcement options. Its usefulness depends on reliable information about the existing geometry, deterioration, materials, and boundary conditions. An analytical model supports engineering judgment; concealed conditions still require investigation.
Designing Repairs That Can Be Built
Repair should address the source of corrosion and restore the required strength, stiffness, support, and restraint. Options may include replacing a lintel, reinforcing a connection, restoring a bearing, or replacing steel that has deteriorated beyond practical repair. Masonry, concrete, and corrosion protection may also require attention.
The selected solution must account for access, welding or bolting feasibility, temporary support, and the sequence in which loads are transferred. In an operating industrial facility, equipment clearances and shutdown requirements can influence which repair is practical. Adding a reinforcement plate over an unassessed corroded interface can conceal deterioration and leave the original weakness unresolved.
Preserving Existing Buildings and Industrial Facilities
A well-supported assessment can help owners distinguish components that can remain in service from those requiring reinforcement or replacement. Where technically justified, targeted rehabilitation offers a way to retain serviceable construction, limit demolition and material use, and manage disruption to occupants or industrial operations.
These decisions connect local engineering details with broader objectives: protecting people, maintaining reliable facilities, and extending the useful life of existing structures. A damaged lintel affects the masonry above an entrance. A deteriorated equipment support may affect a production area. Both require a repair strategy grounded in how the structure actually carries its loads.
Structural Assessment of Corrosion Damage
Sepco Consulting Engineers provides residential structural engineering and commercial and industrial building condition assessments in Ontario. The practice integrates structural assessment, forensic investigation, and steel connection engineering to evaluate existing conditions and develop practical strengthening and rehabilitation solutions.
If you notice cracking around steel lintels, deterioration at beam supports, or separation at corroded connections, an assessment can help identify the cause, determine whether further investigation is needed, and establish an appropriate repair scope.
To discuss a structural concern, send photographs and the property address to info@sepcoengineering.com.
Technical References
- Federal Highway Administration, Peer Exchange Report on Corrosion Prevention and Mitigation for Highway Bridges. The pack-rust mechanism described in this bridge guidance is relevant to comparable steel interfaces in buildings; building-specific assessment remains necessary.
- Brick Industry Association, Technical Note 31B: Structural Steel Lintels.
- Brick Industry Association, Technical Note 18: Volume Changes, Analysis and Effects of Movement.
- Grassl and Davies, Lattice modelling of corrosion induced cracking and bond in reinforced concrete.
- Brick Industry Association, Technical Note 46: Maintenance of Brick Masonry.
- Quantification of the actual expansion and deposition of rust in reinforced concrete.
- Nickless and Atadero, Investigation of Mechanistic Deterioration Modeling for Bridge Design and Management, CDOT-2017-05, particularly the model-specific cracking pressures discussed on page 61.