Metals are often thought of as strong, durable and long lasting, and generally speaking this is correct. However, if the steels surface is not sealed with a protective coating, it can corrode. Metal outdoor furniture loses visual appeal and eventually their structural integrity. There are hundreds of steel surface coatings to choose from, with most designed to prevent corrosion and increase aesthetic appeal.
Read on for further information on the types of surface coatings commonly used by street furniture manufactures.
Zinc Electroplating
A very thin layer of zinc is imparted onto the surface of the metal using electrolysis. Generally street furniture items that are zinc plated are also painted as well. Zinc plate and powder coat can offer good service lives of up to 15 years in low-corrosive environments. However, it is not suitable in coastal areas, other corrosive environments, or where vandalism and “hard” use is present. It is a relatively cheap process.
Hot Dip Galvanising
Metal components are dipped into a molten tank of zinc, leaving behind a thick coating. Used extensively in outdoor products, galvanising protects against corrosion. This is due to the high volume of zinc in the coating. Galvanised products initially have a bright silver look, but after several months will take on a matt grey finish. Galvanised steel products can also have a secondary finish applied, such as powder coating. This gives the advantage of both a good corrosion protection and a visually appealing finish. However, there are several steps that need to be taken to ensure good adhesion and finish. This includes etching and de-gassing. Galvanising is more expensive than zinc plating, but is still reasonably economical. Galvanising creates a high level of protection against corrosion and is suitable for most environments.
Mechanical Galvanising
Components are placed into a rumbling drum with zinc powder and plastic shot. The rotating action of the drum imparts the zinc onto the surface of the components. With similar protection levels to hot dip galvanising, the main advantage of this process is the uniform coating. It’s free from dags and slag that can be associated with hot dip. Due to the nature of the application, this process is only suitable for small components such as brackets and fasteners. Labour costs increase when the de-burring of hot dip galvanised parts are required.
Zinc Rich Primers
A primer containing zinc is applied to the material prior to a finish coat. This is done by powder coating or a wet coat paint process. Depending on the type of primers and paints used, protection levels vary. This generally offers a medium level of protection, but is usually a more expensive process. It is not suitable for areas where surface finishes are likely to be broken by physical damage.
Zinc Plated Sheet Steel
An alloy of aluminium and zinc (zincalloy, zincallume etc) or zinc (gal sheet) is applied in a production line. The sacrificial properties of zinc will protect the raw edges, even when cut to shape. But if large areas of the finish become damaged during fabrication, areas can become vulnerable to corrosion. This is a very cost effective method that has a good level of corrosion resistance. However, it is acceptable only for low corrosive environments.
Powder Coating
The metal components are coated with a primer, or a layer of powdered polymer. The coated parts are baked in an oven to melt the polymer, resulting in a very smooth and consistent finish. Powder coat generally offers low levels of corrosion protection and for street furniture is really only an aesthetic finish. Powder coating is suitable for steel and aluminium and is a cost effective and consistent finish. There is also a large range of colours available.
2 Pak Painting
Components are coated with a primer and a two-part top coat. This top coat consists if a base and a hardener. 2 pack paints offer a very hard wearing surface and a high level finish. Depending on the primers used, 2 packs main defence against corrosion is sealing the base material from the atmosphere. Due to the extreme durability of good quality 2 pack paints, this can offer a very high level of protection; however it relies heavily on the surface. If the surface layer is damaged, corrosion can spread underneath the paint. 2 Pak’s finish is very high quality and lasts longer than a powder coat finish. For this reason, 2 pack paint is generally a more expensive finish than powder coating.
Anodising (Aluminium)
Components undergo an ectrolytic passivation process used to increase the thickness of the natural oxide layer on the metals surface. In simpler words, aluminium naturally gains a skin that protects it from further corrosion. Anodising thickens this skin. Generally speaking, all aluminium outdoor furniture should be anodised. This stops the surface from becoming cloudy and unsightly, particularly in corrosive environments. Anodising is also a suitable preparation for powder coat. Anodising is a cost effective process. It has a very high level of corrosion protection, making it suitable for coastal areas.
Draffin Street Furniture has vast experience with metal surface coatings. If you have and questions or need advice when specifying a surface coating please contact one of our friendly engineers. We love to put our experience and resources to work helping solve our customer’s problems.