Rust jacking is one of the most destructive yet often hidden deterioration mechanisms affecting older and moisture‑prone buildings. It occurs when embedded steel components begin to corrode, producing iron oxide that expands dramatically and exerts tremendous force on surrounding materials. Over time, this process can crack, deform, or entirely displace masonry, concrete, stone, and even heavy structural elements.
What Causes Rust Jacking?
Rust jacking begins with corrosion of iron or steel in the presence of moisture and oxygen, often occurring where water infiltrates exterior walls, structural pockets, or concealed spaces. Once corrosion begins, rust occupies a significantly larger volume than the original steel. There have been documented cases demonstrating expansion of up to 10X.
- The oxidation process generates extremely high internal stresses of sufficient force to deform or fracture building wall assemblies when confined in masonry or concrete.
Because many steel elements in older buildings were placed directly against masonry without proper coatings, moisture migration through walls readily initiates corrosion.
How Destructive Can Rust Jacking Be?
The expansion force created by rusting steel is powerful enough to crack stone, brick, concrete, and terra cotta. Typical observations in the field include:
- Cracking and spalling of adjacent masonry, as expanding corrosion products push outward or upward. Step cracking in brick masonry is a very common symptom of rust jacking.
- Spalling in concrete walls, floors or structural framing members caused by corrosion of the steel reinforcement embedded within.
- Steel sections can experience significant dimensional change: one case study showed a 3/8‑inch (9.5 mm) steel flange expanding to 1⅝ inches (41 mm) due to rust accumulation.
While not always immediately compromising the entire structural member, rust jacking can mask underlying section loss—and once section loss reaches 10–20%, engineers recommend deeper evaluation and potential repair or replacement.
Why Rust Jacking Is Particularly Dangerous in Existing Buildings
Older buildings, especially masonry structures from the early 20th century, commonly have unprotected steel embedded directly in porous exterior envelopes, like brick masonry walls. This creates a perfect environment for:
- Hidden deterioration, since corrosion often develops out of sight behind facades.
- Accelerated moisture intrusion, as cracks caused by rust jacking allow additional water to enter, creating a destructive feedback loop.
- Higher long‑term repair costs, as restoration frequently requires removing cladding, cutting out deteriorated steel, and reconstructing damaged areas.
In reinforced concrete, corrosion‑induced expansion can lead to concrete cover cracking, exposing rebar and rapidly worsening its deterioration. Studies show that the expansion of rust products creates sufficient force to rupture concrete layers, eventually reducing the structural integrity of beams, slabs, and columns.
Prevention & Mitigation Measures
Fortunately, rust jacking can be slowed or often prevented when proper measures are implemented:
- Control Moisture Infiltration
- Ensure effective exterior wall waterproofing.
- Repair failed mortar joints, sealants, or flashing details that allow water ingress.
- Protect Exposed and Embedded Steel
- Apply high‑quality anticorrosion coatings or paints; these significantly reduce oxidation by limiting exposure to moisture.
- Use corrosion‑resistant materials (e.g., galvanized or stainless steel) for replacements and repairs.
- Improve Drainage and Ventilation
- Promote drying of concealed spaces, reducing the availability of moisture that drives oxidation.
- Perform Regular Inspection of Vulnerable Areas
- Lintels, shelf angles, anchors, and embedded steel in masonry should be inspected for early signs of displacement or cracking.
- Engineers may remove small sections of cladding to observe concealed steel conditions where necessary.
- Address Corrosion Promptly
- Remove rust scale to assess actual section loss.
- Replace or reinforce compromised steel members.
- Rebuild damaged masonry or concrete once the underlying cause has been corrected.
Conclusion
Metals can be found in buildings as basic components of the structure. They are also found in devices and systems used to support and/or anchor façade elements. Corrosion is the most common form of deterioration of metals in buildings. It is an electrochemical oxidation process that results in the deterioration (separation and loss of mass) of the metal.
Rust jacking may begin quietly, but its consequences can be severe, leading to cracked masonry, spalled concrete, displaced building components, and compromised structural integrity. Because rust can expand steel components up to tenfold in volume and exert enormous internal stress capable of fracturing nearly any building material, early detection and preventive measures are critical.
For owners and facility managers of aging buildings, establishing a proactive inspection and maintenance plan is the most effective strategy to preserve structural health, control repair costs, and prevent unexpected failures caused by this powerful yet preventable form of deterioration. Such maintenance typically includes repointing masonry joints, installation of sealant repairs as appropriate, and repairing cracks in the masonry regularly.
Sr. Building Envelope Consultant
Duffy Engineering
