What is Oil-Canning?
Oil-Canning is associated with all thin sheet metal products and occurs in the wide flat portions of the cladding profile. It seen as a series of standing waves, or regular bumps and hollows alternating along the flat length of the panel. This waviness, when viewed under certain conditions, can be undesirable aesthetically and may not meet the owner’s expectations.
The cladding manufacturers are aware of the potential for oil-canning in the cladding profiles and can help minimize the effect. It is important for the proper steps to be taken during manufacturing and installation to produce a quality finish product. Quality however, cannot end on the shop floor. The building project needs the cooperation and knowledge of everyone involved to enhance the quality of the finished job. Oil-canning is a phenomenon that can be managed if the following factors are considered at the beginning of the project.
Common Factors that Affect Oil-Canning
Sheet Thickness: Generally, the ticker the steel, the flatter the profile can be maintained. For some products, however, this may not always be the case. The manufacturer can advise on the best option.
Flat Width of Cladding Profile: The addition of stiffening ribs or ridges “brakes up” the surface and reduces the flat width of the profile. The narrower the flat width of the cladding element the harder it will be for that area to develop into noticeable oil-canning waves. If wide flat elements are necessary, then more attention should be paid to the other factors that can reduce the possibility of serious oil-canning like; leveled and smooth decking.
Temperature: The expansion and contraction of the cladding sheet due to changes in temperature creates stresses that will exaggerate oil-canning. The surface temperature of the cladding will cycle throughout the year and even fluctuate daily. The amount of fluctuation depends on several variables such as project location, building orientation, cloud cover, surface finish, color and solar absorption characteristics. The impact of temperature changes on the panel appearance can be exaggerated if the perimeter flashing conditions inadvertently restrain the panel. Only fasten one end of the sheet to allow for expansion and contraction. Shorter panels lengths can also help these stresses. The use of expansion type hold-down clips that allow the panels to expand and contract can be helpful for metal roofing applications.
Cladding Orientation: Cladding panels can be installed either vertically or horizontally to achieve different architectural effects. The appearance of oil-canning in a vertical application is less pronounced than in a horizontal application due to the different way the eye of the observer perceives the standing waves.
Paint System and Color: The nature of the paint system selected for the cladding is a strong contributor to controlling the visual impact of oil-canning. Lighter colors will reduce the visibility of oil-canning where the identical cladding in a dark color will highlight any irregularities. Paint system with textured finishes and lower gloss will also be less likely to show oil-canning.
Cladding Slope: The slope of the wall or roof on which the cladding is mounted will affect the visibility of oil-canning by changing the angle of incidence of the reflected light. Vertical applications with the light striking the surface at high angles of incidence perpendicular to the length of the flat element will reduce the visibility of oil-canning.
Handling: Carrying of panels in the flat, or twisting of the panels during lifting, can induce a wavy appearance to a previously flat panel. Twisting can occur if one corner of the cladding panel is used to lift the panel or to remove the panel from a bundle.
Fastening: Over-engagement of the cladding panel and over-driving of fasteners are two installation-related factors that can contribute to oil-canning. Most panels accommodate transverse thermal expansion by flexing of webs and by “take-up” at side laps. When panels are over-engaged, these relief features are hindered or eliminated, particularly for the flat panels without corrugations. Installing the fasteners requires some control to ensure that the fastener is not over-driven. An over-driven fastener will pull don the classing locally and can create noticeable deformations.
Movement of the Primary Structure: If the primary structure moves due to differential deflection, racking, drift or settlement the amount of oil-canning can be increased. This type of oil-canning can be temporary as the structure continues to move, or could be permanent depending on the root cause of the movement.
Subjective Assessment: The acceptance of oil-canning (if present at all) is a very subjective assessment between different observers. If the building project demands a very tight control on the possibility of oil-canning, then extra attention needs to be given while specifying the cladding product.
Preventive Measures: Some degree of oil-canning will occur in all flat panels but only in few cases is the amount considered unacceptable. It is important to recognize that it is always best to prevent oil-canning; corrective measurements after the cladding is installed are usually very limited. Many uncontrollable factors contribute to oil-canning and no cladding manufacturer or installer can assure the total prevention of oil-canning on any project. Preventive measurement that consider all the contributing factors are the key to a successful project.
Oil- canning is an aesthetic issue only. Structural integrity is typically not affected.