At AEP Span, we understand the critical role that precise field cutting of metal panels plays in the durability and aesthetic quality of your roofing and siding projects. With over 50 years of experience providing high-performance architectural metal profiles, we prioritize technical expertise and quality to help you achieve outstanding results in every build.
There can be installation complexities when creating a weathertight metal roofing solution. Cut edges are no exception. Factory cuts are those made to the panels and flashings during the fabrication of the roof system. Factory cuts are made using a shear during the manufacturing process. This ensures a clean panel cut without damage to the paint or metal.
The Importance of Proper Field Cutting Metal Panels
Field cuts are often necessary, as factory cuts may not work or be practical for certain transitions or roof conditions, such as hips, valleys, roof penetrations, or a variety of other conditions that can exist on a roof. While factory cuts are precise, on-site cuts and adjustments are often required for proper installation. Improper field cutting, however, can leave exposed edges susceptible to unsightly workmanship or worse yet, corrosion at the cut edge of the material.
Risks of Sawing & Abrasive Cutting
Factory cuts use specialized shearing processes, akin to the action of scissors, to ensure clean and precise edges. This method helps maintain the integrity of the protective coatings, such as ZINCALUME® which act as sacrificial layers to prevent corrosion. In contrast, sawing or abrasive cutting can leave jagged edges and produce heat that damages these coatings, leading to potential corrosion issues.
Abrasive cutting generates “swarf” (fine metallic filings, and fragments). These tiny particles, often invisible to the naked eye, are unintentionally left on the metal surface. If left unchecked, they can corrode and cause rust stains, leading to permanent visual deformities on the metal product.
The two photos on the left show a metal panel being field cut using a grinding disk. The second photo shows the swarf left behind from a grinding disk on the metal panels that have corroded and stained the metal panels.
Recommended Tools for Field Cutting
There are several reasons factory-produced panels require cutting on a job site. To maintain the quality and durability of AEP Span metal roofing & siding panels, we propose the following tools for field cutting:
Hand Tools
The following hand tools are preferred as they utilize a clean shearing motion.
Aviation Snips: For precise cuts, available in left, right, and straight cutting versions.
Sheet Metal Shears: A heavy-duty, long-handled pair of metal cutting scissors with short blades.
Guillotine-style shearing blades: The most popular is a portable hinged device manufactured by Swenson Shear. It is commonly used to field cut corrugated or trapezoidal ribbed panels at right angles to the ribs. Swenson Shear also manufactures a portable field table for notching standing seam panel ribs.
Electrical Power Tools
Nibblers: Handheld oscillating punch-and-die tool that removes small pieces of metal. Note, when using this tool, it’s difficult to cut in a straight line and can be challenging to cut up-and-over standing seam or trapezoidal ribs.
Power Shears: Electric scissors that produce clean cuts with minimal burrs. This is a good tool to cut parallel to ribs or for cutting the flat pan of a standing seam panel, but it’s difficult to cut across a panel.
Using high-quality tools helps ensure clean cuts and reduces the risk of corrosion. To achieve the best results, tools should always be kept sharp and well-maintained. Improperly cutting prefinished panels on a job site can create severe performance issues. If an improper cut edge is exposed to weather, the cut panels can create corrosion and finish deficiencies that will compromise the material and paint finish warranties.
The Misunderstood Aspect of Cut Edge Protection
Metal roofing installers and users do not need to be concerned about corrosion at cut edges when field cutting metal panels correctly. While the edge is exposed, the base carbon steel is encased by a metallic coating on both sides. Over time, galvanic action causes zinc compounds in the coating to automatically build up at any cut edges to prevent corrosion. Additionally, when metal is cut in a shearing action, small amounts of the metallic coating can be folded over the exposed base metal to provide additional protection. For particularly harsh environments, consider hemming panel edges to conceal and shield them from exposure. Irregular cutting motions such as sawing or abrasive cutting may introduce impurities to the cut edge or create inconsistent pathways for the metallic coating to encase the cut edge, increasing the risk of corrosion.
The Science Behind Self-Healing Properties
In service, galvanic action causes zinc compounds to automatically build up at any cut edges or scratches through an electrolytic reaction when water or moisture is present. This process slows the rate at which the surrounding coating is consumed around damaged areas, sometimes referred to as the “self-healing” property of ZINCALUME® coatings.
Superior Cut Edge Protection in Severe Environments
In more severe environments, ZINCALUME® offers superior cut-edge protection. Unlike galvanized coatings, which are purely sacrificial, zinc and aluminum are included. While zinc will corrode preferentially, aluminum acts as a protective barrier, slowing the spread of corrosion and the rate at which this coating is consumed. For additional protection, particularly in harsh environments, consider hemming panel edges to conceal and shield them from exposure.
Are Cut and Exposed Edges a Source of Corrosion?
The short answer is no. Field cutting metal panels with exposed edges are not a significant source of corrosion. However, this depends on installation and environmental factors. In general, several reasons underpin why exposed edges are not a source of significant concern:
- The zinc in the ZINCALUME® coating acts as a sacrificial layer.
- The self-healing properties of the coating slow down the rate of corrosion.
- Additional protective measures, such as hemming, can be employed in extreme environments.
In Summary
In summary, following proper field cutting techniques and using recommended tools will help ensure that your AEP Span metal panels perform as intended and maintain their aesthetic and functional qualities over time. Always consult with our technical services team for specific recommendations and best practices tailored to your project needs.