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Cut Edge Corrosion – what (not) to do

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Our commercial roof surveys often identify signs of cut edge corrosion on metal roof cladding. Cut edge corrosion typically starts as edge peel at the cut edges of a metal sheet. Through the action of natural weathering over time, the exposed edge can start to corrode and the process rapidly accelerate, particularly at the sheet overlap as a result of capillary held rainwater.

Edge corrosion is a progressive problem. Left untreated, it can cause the protective coatings to peel away, revealing bare metal and further corrosion. What’s more, it can develop away from the cut edge, destroying the weather-sealed lap joint and gutter overhang, and ultimately threaten their waterproofing function.

Early detection and effective treatment is highly advisable to prevent costly future sheet replacement.

Here’s how not to do it:

Cut Edge Corrosion

 

We came across this truly terrible example of cut edge corrosion treatment on a recent building survey. There’s clear evidence of poor preparation and the product having been (badly) applied over a cloth tape – what we call a ‘botch job’ in the trade.

What causes cut edge corrosion?

Pre-finished roof sheeting is cut to size at the manufacturers to fit the building layout. If the cut edge is not sufficiently weather proofed, thin lines of metal are left exposed, leaving the roof vulnerable to corrosion. The roof cladding will be coated prior to cutting but this typically won’t suffice as a weatherproof, waterproof coating for the edges, leaving them susceptible to peeling, corrosion and delamination.

Cut edge corrosion is most visible along horizontal edges such as overlays, seams and eaves. Unfortunately, this means that the damage will often not show up during a general inspection ‘from the ground’ or inside a facility, since water spreads through capillary action.

Regular maintenance checks

Repair work and roof sheet replacement for large commercial building can be very costly and disruptive to day-to-day operations, which is why we always recommend that regular roof audits should be carried out on the condition of the cladding.

Weathering, oxidation and pollutants all accelerate the degradation of the cladding. Regular manual checks should be conducted along metal guttering to make sure gutter overhangs are not blocked or ill fitting. Water and chemical build-up in a gutter can further degrade the cut edge and cause roof leaks.

As corrosion takes hold, aluminium and steel become increasingly brittle. Neglecting to carry out regular maintenance checks may mean the cladding can no longer be repaired, requiring expensive replacement.

How to protect your roof

Refurbishing and protecting commercial roofing and cladding is best achieved by installing waterproofing systems for metal roofs, using high performance liquid membranes. Coatings can be applied to a number of surfaces on industrial or commercial properties. This won’t just improve the overall look of the building but also protect against weather damage and corrosion.

At Bradley-Mason, we’ve recently had great results with Sika Liquid Plastics, a tried and tested effective surface treatment for the onset of cut edge corrosion. Designed to extend the lifespan of the roof surface, sheets remain structurally sound without compromising the waterproofing function.

Here’s a recent before/after example:

 

Roof coating - project image

 

Roof coating - project image

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