Definition of Oil Canning:
Oil canning is the visible distortion or waviness visible on flat areas of metal cladding and roofing.
The level of this waviness is directly associated with the type of material, surface reflectivity of the material and the ambient temperature- both at time of installation and time of viewing.
Type of material and ambient temperature: materials behave differently and have unique properties regarding thermal expansion and contraction. Aluminium has a thermal co-efficiency of 2.4mm per m @ 100 degrees centigrade. This means that the material will expand and shrink 2.4mm per m @ 100 deg C- obviously we will not experience 100 degrees but may get close to 50 degrees C.
It would therefore be advisable to slot fixings to allow for this movement along the length of the material. Titanium Zinc has a thermal co-efficiency of 2.2mm per 100 degrees C, Copper is 1.7mm and Steel sheet including Colorbond is 1.2mm.
Surface reflectivity: the level of gloss on a flat surface directly affects the degree of visual distortion, the more matt the colour the flatter the material appears. Shiny metallic surfaces have a high degree of light reflection and therefore appear to have far worse oil canning.
Other factors that can affect the visual appearance of sheet metal:
There are further numerous causes through manufacture and installation that can also attribute to Oil Canning these can be listed as follows:
Original coil not being completely square and the exact same thickness across the width. This means that one side of the slit strip may have a slightly thicker gauge when compared with the opposite side. The resultant roll-formed panel may have a camber lengthwise resulting in distortion when pulled straight.
A blunt slitting blade can stretch the material as it runs through a slitter this will result in the slit strip being flat one side but wavy on the other. Once roll-formed this too will lead to waviness in one side of the pan.
Choice of profile can also determine the flatness of a profile- where both sides are similar in section such as Archclad Express™ Panel, Archclad Cliptray 48™ and Archclad Standing Seam 25mm there is similar pressure imposed to both sides during roll-forming- however Cliptray 25mm has a very different cross-section between the male and female rib and more stress is applied to the male leg causing long panels to camber in length.
Substructure needs to be as plumb and flat as possible with minimal deviation in level- any discrepancy here will be noticed immediately as panel will distort and be stressed.
Panels must be installed in a relaxed form- over engagement and forcing panels into each other will cause stress across the flat face and cause distortion.
Due to the thermal movement discussed above under What is Oil-Canning item 1- we recommend slotting fixings to Archclad Express™ panel to assist with natural thermal movement. Ensure the fixing is the correct size for the slot and not overtightened as this will prevent movement.
Handling panels can also cause damage or stress. Panels need to be carried vertically, not flat, to reduce damage.
Ensure the installer has the experience to install your project and is aware of the intricacies surrounding thermal movement and material performance.
Machinery designed to roll-form these modern, innovative Architectural products are designed for non-ferrous materials. A characteristic of non- ferrous metals is their ability to form and remain completely in the formed shape. Steel unfortunately has a certain spring and even using 0.55mm Soft feed Commercial Grade material designed for the roofing and flashings industry, there still is a certain amount of spread after roll forming.
Due to this design in roll-forming for softer non- ferrous material the tolerances and pressures applied are designed for 0.8mm – 1.0mm Non-ferrous materials- when 0.55mm steel is substituted the tolerances at side laps are not a tight as intended and somewhat loose.
Level of surface gloss:
The visual distortion of flat metal surfaces is directly related to the level of gloss of the surface finish. With shinier surfaces the tiniest blemish is immediately noticed- the same item on a SATIN or MATT finish will almost disappear completely- bear in mind though, it can never be entirely eliminated.
In a scale of 1-5 from least noticeable distortion to most noticeable distortion we would list our products as follows:
PVDF Original Range Aluminium
Satin Black, Cirrus White, Metallic Silver = 1
Silver Grey = 3
PVDF Naturel Range
All colours = 2
PVDF Premium Range
Patina Grey = 1
Light and dark bronze = 5
Standard Range Colorbond
Night Sky, Manor Red = 4
Balance of the range = 3
Matt Range Colorbond
All colours = 1
Copper Mill Finish
Mill finish = 5
After patina formation = 2
Mill finish = 5
After patina formation = 2
Standard Colour ranges =2
Raw state = 5
After patina formation = 1
Design of panel width and thickness:
There are two ways to stiffen panels, the first being to reduce the effective cover of a panel and the second is to increase the thickness of the material.
The roll formed sides of all panels stiffen the immediate area - therefore the narrower a panel is more rigid the panel will be.
However, a narrow panel will not always suit the design and is often more expensive due to wastage of material in forming the folds. In this case increasing the thickness of the material may be an option. A point to consider here though, is availability, minimum order quantities and extended lead times.
All Archclad PVDF Aluminium Range is stocked in 0.8mm thickness and we recommend panel widths specifically to reduce Oil-Canning and maximise the coil width to reduce wastage and cost.
Oil- Canning is a visual problem and will not affect the performance of the product or installation.
By being aware of the points above we can possibly reduce the chance of noticeable distortion but will never entirely eliminate this natural phenomenon.
As a supplier and manufacturer, Archclad has invested in the very best European equipment available, expertise and staff to manufacture the best materials available- but even with all this care we cannot guarantee that there will not be some form of Oil-Canning in the finished product on site and therefore a degree of oil-canning is an acceptable Industry Standard and does not form a basis to reject the finished product.