Arguably more than for any other piece of street furniture, the selection of materials for a signage product is vitally important. Primarily, every material must be carefully selected to ensure a long service life of the sign, and particularly that the graphic elements remain crisp and legible. External signage, by its very nature, is exposed to the elements 24 hours a day 7 days a week, therefore materials that will not rapidly corrode or degrade are required.
As the weight of the finished sign is not normally a concern, one of the most economic materials with which to make the internal structure is galvanised mild steel. Steel itself is relatively cheap and easily cut, formed and fabricated. The galvanised layer, while not particularly pretty, will protect the steel for many years by acting as a sacrificial layer; it does this by corroding in preference to the steel and the rate at which the zinc in the galvanised layer corrodes is much slower than that of bare steel. Adding paint or powder coat over the top of the galvanising not only allows the introduction of colour, but further protects the steel by adding an additional layer of protection from the environment.
Anodised Aluminium Fingerpost
Fabricated steel alone can be limited in its applications since commonly available sections and sizes are limited. Aluminium allows for more intricate shapes to be created through the use of extrusions and complex formed shapes. Raw aluminium is a highly reactive metal that oxidises very quickly; the advantage over steel being that this oxide layer protects the metal underneath and is much harder than the base material. The oxide layer, which is only normally a few microns thick, can be made thicker by anodising the aluminium - a process that thickens the protective layer by passing an electrical current through the metal while submerged in an acidic bath. The thicker the oxide layer the better protected the aluminium and a typical thickness for external architectural use is 25 microns, while interior grade anodising might be only 5-10 microns. Again, aluminium can be painted or powder coated, but colours can also be introduced during the anodising process through the use of organic dyes. These produce bright, vivid colours but can be affected by UV in sunlight unless special architectural grades of dye are used. In addition, electrolytic colours can be added to the anodised layer; while they do not offer the range of colours available through organic dyes, they are colour fast as the hues are produced using metallic compounds. It’s worth noting that aluminium is more difficult to weld than steel and welded areas do not take anodising well, usually creating dark grey to almost black areas along the weld seam.
One of the most stable materials for use in signage is stainless steel. Two grades are commonly used, ANSI 304 and 316; 304 grade being slightly cheaper than 316, but having a slightly lower resistance to corrosion. If the sign is to be installed in a coastal location it is highly recommended that only 316 grade is used in order to minimise the chances of corrosion. The corrosion resistance is further enhanced by electro-polishing as it reduces the size of the small pits on the metal’s surface, making it easier to clean, and less likely to hold on to contaminants which lead to corrosion. In a non-coastal environment 316 grade stainless steel is recommended, but can be used without the need to be electro-polished. This allows alternative finishes such as brushing, graining, bead blasting or polishing to be applied. 304 grade stainless is highly suited to interior signage or in areas that are relatively protected from the elements.
For non-structural components there is a much wider variety of materials available:
UV stable plastics such as acrylic and polycarbonate can be cut, formed and molded to produce curved and domed surfaces as well as allowing elements of the sign to be illuminated producing a soft glow. Long lasting vinyl graphics can easily be applied to a sign’s exterior surface, providing a n affordable way to add information or branding to a sign’s panels. Glass is a very tough and durable material which is mostly used to protect the key information on a sign. Vinyl graphics applied to the reverse side of a glass panel will be resistant to physical damage and, if sealed properly, will also resist environmental damage for many years. Obviously lower tech solutions, such as paper, can be fitted behind glass panels, and these are suitable for optional back illumination.
Vitreous enamel, or VE for short, is one of the toughest and most durable sign materials available. It is a ceramic glass-like material that is applied layer by layer onto a steel substrate. Each colour used on the sign requires its own screen to be produced, the slurry applied and then fired in an oven. Due to the amount of labour and time it takes to apply the graphics, VE is not a cheap material, the cost increases with each colour added to the graphic and also with the intricacy of the graphics. However it is incredibly durable and resists most attempts of vandalising, while remaining colour fast for its lifetime delivering a competitive whole-life cost. Due to its stability as a material, it is very easy to clean and maintain.
Stone is an incredibly durable material that will most likely outlast not only the life of the sign, but probably the life of the area in which the sign is installed since most urban areas are regenerated every 20 years or so. Certain stones can be expensive, in part due to difficulties in shaping and forming and, with recent developments in concrete, very slim and complex forms can be created to look like stone, with many grades of finishing from acid etching to polishing at a fraction of the cost of stones such as granite and marble.
With such a diverse palette of materials and finishes available, the signage specifier has a huge combination of suitable materials and finishes to choose from. Through this extensive selection, signage can be employed not only to serve a purely functional purpose of displaying local information but also to improve or complement the identity of a project through a vernacular approach.