Chris Brandrick, Technical Director of Giromax, discusses advances in the treatment of Cut Edge Corrosion on Profiled Steel Roofing and the reasons they were necessary.
CUT EDGE CORROSION
Roof sheet manufacturers’ performance statements refer to the lifetime of the pre-finished steel sheet in terms of the period when the building owner must consider whether to re-paint the sheet, either to upgrade the aesthetics or to preserve protection of the steel substrate. Within that lifetime, coating edge peel may arise from normal weathering. It is most often seen at sheet overlaps and at eaves and gutter overhangs, and if neglected, this may develop into Cut Edge Corrosion which can eventually compromise the structural integrity of the sheet.
The development of Cut Edge Corrosion is difficult to predict. It is progressive by nature and accelerates in proportion to the accumulation of conductive elements especially capillary held water, eventually overcoming the protective sacrificial barrier which is usually zinc or a zinc alloy. Ideally, long sheets from ridge to eaves should be specified, reducing the need for overlaps. In practice, this is not always possible where long runs or translucent sheets are required.
If the problem of Cut Edge Corrosion has subsequently arisen, it is recognised that its treatment must necessarily follow a specification that excludes water from the lap, without the ability to lift and reset the roof sheets. In addition, the joint must remain flexible enough to accommodate stresses from building movement, sheet expansion and foot traffic and withstand extremes of weathering, temperature, and UV. This is a difficult specification to achieve and one that was best serviced for many years by the use of a silicone based system. Successful treatment however, depended on two key factors which inevitably could be viewed as system limitations.
THE LIMITATIONS OF SILICONE
Firstly, corrosion control depended entirely on the adhesion properties of silicone in being able to smother and starve the substrate of the two main agents of corrosion - air and moisture. Using silicones, such adhesion can only be achieved on a completely dry surface and since moisture cannot be fully displaced from the lap joint, adhesion cannot be guaranteed with sealant alone. The compromise was to augment it with a brushed version that relies entirely on its making contact above and below the lap, classing it as an external seal.
Secondly, for this seal to work, to fully accommodate sheet movement without splitting, the application must remain flexible. Silicones have a high level of flexibility but remain relatively soft, especially during their curing cycle, which makes them particularly vulnerable to impact and abrasion damage, especially on a roof where they attract the attention of birds.
ADVANCES IN TREATMENT -
GIROSIL® EDGE RC-E
With these limitations in mind Giromax have introduced a more technologically advanced solution. GIROSIL® uses the latest hybrid technology that takes full advantage of properties developed to overcome the application restrictions and wear limitations of silicone alone.
Fully moisture tolerant, the GIROSIL® system can be applied to all surfaces, wet or dry, speeding up application times and helping meet project demands.
For effective corrosion control, GIROSIL® doesn’t rely solely on its tenacious adhesion. GIROSIL® Basecoat penetrates and binds with corrosion at the molecular level, using laminar flake technology to form a hard barrier that prevents air and moisture from reaching the substrate.
Laminar flake is also found in GIROSIL® SE, a moisture tolerant sealant that fully contacts with all surfaces to secure a full inter-lap seal. It uses the same base structure as GIROSIL® Edge RC-E, the coating that completes the lap encapsulation that results in a tough, UV resistant system that fully satisfies the demand for both corrosion control and flexibility without sacrificing impact and abrasion resistance.
FOR FURTHER INFORMATION -
GIROSIL® delivers market leading Performance, Choice & Reliability. For further information click here to view our revolutionary new product range, all fully guaranteed for up to 20 years.
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