Cladding Corrosion

Cladding corrosion is the progressive degradation of a building’s external skin caused by environmental, chemical, or electrochemical reactions. In the UK, this typically manifests as oxidation or pitting on metal cladding, weakening the structural integrity of the facade and compromising the building’s aesthetics and weatherproofing capabilities. If left unaddressed, corroded cladding can lead to water ingress, panel failure, and significant long-term remediation costs.

Key Takeaways#

• Early detection is critical: Identifying metal cladding corrosion in its early stages can prevent the need for full replacement.
• Environmental factors matter: Buildings in coastal or industrial areas of the UK are at significantly higher risk of accelerated facade corrosion.
• Systemic approach: Effective cladding testing identifies whether corrosion is superficial or indicative of deeper structural issues.
• Material specific: Aluminium, steel, and zinc all corrode differently; treatment must be tailored to the specific substrate.
• Compliance: Addressing corrosion is a key part of maintaining a "Safe State" under modern UK building safety legislation.
• Repair vs Replace: Cladding corrosion repair is often viable for localised damage, but widespread systemic failure may necessitate a full reclad.

Understanding Cladding Corrosion#

In the context of the UK’s built environment, cladding corrosion refers to the chemical breakdown of the external wall system’s metallic components. While we often think of the visible outer panels, corrosion frequently occurs out of sight, affecting the rails, fixings, and brackets that hold the facade in place.

The UK climate, characterised by high humidity and frequent rainfall, provides the ideal electrolyte for galvanic and atmospheric corrosion. For property managers and building owners, understanding the mechanism of this decay is the first step toward effective asset management.

Common Types of Facade Corrosion#

Not all corroded cladding looks the same. Depending on the material and the environment, the degradation can take several forms:

• Uniform Corrosion: This occurs evenly across the surface of the metal. While unsightly, it is often the easiest to predict and manage.
• Pitting Corrosion: Small, deep holes form in the metal. This is particularly dangerous as it can penetrate through a panel while the surrounding surface appears relatively healthy.
• Galvanic Corrosion: Occurs when two dissimilar metals (e.g., aluminium panels and steel fixings) come into contact in the presence of moisture, causing one to corrode at an accelerated rate.
• Crevice Corrosion: Happens in confined spaces, such as under gaskets or lap joints, where stagnant water becomes trapped.

Why Does Metal Cladding Corrode?#

The primary driver of metal cladding corrosion is the exposure to oxygen and moisture. However, several catalysts specific to the UK landscape accelerate this process. Coastal buildings face salt-laden air, which contains chlorides that aggressively attack protective oxide layers on aluminium and steel.

In urban environments, pollutants like sulphur dioxide react with moisture to form acidic compounds that etch into the facade. Furthermore, poor design—such as inadequate drainage or the use of incompatible fixings—can create "micro-climates" on the building face that foster rapid decay.

The Impact of Corroded Cladding on Building Safety#

While cladding corrosion is often viewed as an aesthetic flaw, its implications for building safety are profound. The external wall system is designed to act as a unified shield. When individual components fail due to corrosion, the entire system’s performance is compromised.

Structural Integrity and Falling Hazards#

The most immediate safety risk involves the failure of fixings. If the primary support brackets or the rivets holding a panel in place suffer from advanced facade corrosion, the panel may become detached. In high-rise environments, even a small piece of trim falling from height poses a lethal risk to pedestrians and residents.

Regular cladding inspections focus not just on the visible panels, but on the integrity of the hidden support structure to ensure every component remains securely tethered to the building’s primary frame.

Water Ingress and Secondary Damage#

Corroded cladding often develops perforations or "pinholes." These allow moisture to bypass the weather screen and enter the cavity. Once inside, water can degrade insulation, promote the growth of mould, and eventually reach the inner leaf of the building. This often leads to internal damp issues that are expensive to rectify and detrimental to occupant health.

Fire Safety Considerations#

While corrosion itself is not a fire risk, the remediation of cladding corrosion often intersects with fire safety. If a building requires cladding corrosion repair or replacement, it is an opportune time to assess whether the cavity barriers and insulation meet current UK fire regulations. A degraded facade can sometimes mask issues with the underlying fire protection layers, which are only revealed during a detailed technical assessment.

Identifying Cladding Corrosion: What to Look For#

Building owners and managing agents should be vigilant for early warning signs of facade corrosion. Early intervention is almost always more cost-effective than reactive repairs after a failure has occurred.

Visual Indicators of Failure#

• Discolouration and Staining: Rust-coloured streaks on steel or white, powdery deposits on aluminium.
• Blistering Paint: Bubbles forming under the polyester powder coating (PPC) often indicate that corrosion is happening underneath the finish.
• Pitting: Small indentations or "craters" on the surface of the metal panels.
• Surface Chalking: A powdery residue on the surface, indicating the protective coating is breaking down due to UV exposure and chemical attack.
• Loose Fixings: Visible gaps between panels or fixings that appear to be "lifting" away from the surface.

Technical Investigation Methods#

When visual signs are present, a professional investigation is required to determine the depth of the problem. At CladdingTesting.com, we utilise several methods to diagnose the health of a building envelope:

1. Borescope Inspections: Inserting cameras into the cavity to inspect the condition of hidden brackets and rails.
2. Adhesion Testing: Checking if the protective coatings are still bonded to the metal substrate.
3. Thickness Gauging: Using ultrasonic tools to measure how much "healthy" metal remains in a corroded cladding panel.
4. Metallurgical Analysis: Taking small samples (coupons) for laboratory testing to identify the specific alloy and the rate of degradation.

The Lifecycle of Metal Cladding in the UK#

Most modern metal cladding systems are designed to last between 20 and 40 years, provided they are maintained correctly. However, the reality in the UK is that many systems begin to show signs of cladding corrosion much earlier due to a lack of "wash-down" regimes or the use of sub-standard materials during construction.

Environmental Zonation#

The UK is divided into different corrosivity categories (C1 to C5) based on ISO standards. A building in central Birmingham (C3 - Medium) will have different maintenance needs compared to a tower block on the Brighton seafront (C5 - Very High). Understanding your building's zone is vital for determining the frequency of inspections and the type of cladding corrosion repair required.

The Role of Protective Coatings#

Most metal cladding relies on a protective layer—either galvanisation, anodisation, or a paint system like PVDF or PPC. Once this layer is scratched or naturally reaches the end of its life, the raw metal is exposed. Metal cladding corrosion typically begins at the "cut edges" of panels where the protective coating was broken during installation but not properly treated.

Cladding Corrosion Repair and Remediation Options#

When cladding corrosion is identified, the response must be measured and evidence-based. We advocate for a "hierarchy of intervention," starting with the least invasive methods that still ensure long-term safety.

Localised Repairs#

If the facade corrosion is limited to a few panels or a specific elevation (such as the prevailing weather side), localised cladding corrosion repair may be possible. This involves:
- Cleaning and treating the affected areas to remove oxidation.
- Applying specialist primer and high-performance overcoating systems.
- Replacing individual failed fixings with higher-grade stainless steel alternatives.

Systemic Remediation#

In cases where the corrosion is more widespread but hasn't compromised the structural safety of the building, a remediation programme is appropriate. This might involve stripping back the protective coatings across the entire facade and applying a new, warrantied coating system. This is often a viable way to extend the life of a building by 10-15 years without the cost of a full reclad.

Full Cladding Replacement#

There are instances where corroded cladding has progressed too far. If the metal has thinned significantly or the support structure is failing, cladding corrosion repair is no longer a safe or economical option. In these scenarios, a full replacement is required. This allows for the installation of modern, non-combustible materials that meet current Building Regulations and provide superior resistance to future corrosion.