Architectural design on coastal locations involves a set of conditions that makes the choice of durable external materials especially important. These environments are often prone to high winds, stormy weather, dampness and saltwater which can accelerate the deterioration of less resilient buildings.
Wood is not a suitable long-term choice for balustrade in marine locations as greater exposure to weathering and moisture can cause rapid deterioration in timber. It is more advisable to use balustrade comprising glass panels and/or metal. Salt crystallisation can form rust in metals, so metallic balustrade requires careful consideration in terms of its likely reaction to a marine environment. Rust-resistant properties or finishes are vital.
Four types of metal are corrosion resistant:
- Stainless steel
- Copper, bronze or brass
- Galvanized steel
Copper, bronze and brass are expensive materials for use in balustrade. Therefore, most metal used for balustrade in coastal locations is either aluminium or some form of steel.
Stainless steel balustrade
Grade 316 or 316L is the optimal choice of stainless steel grade for balustrade in coastal locations. However, in these conditions it often necessitates a cleaning regime to maintain its finish. Without regular attention, its surface can be tarnished by high levels of airborne salt and high winds in harsh marine environments. For both initial cleaning and ongoing cleaning, it is advisable to use soft, non-abrasive cleaning cloths that are clean and uncontaminated with iron or mild steel.
Issues with galvanized steel balustrade
Galvanized steel is a popular choice for architectural metalwork on coastal sites. The galvanizing process coats the metal with zinc to make it resist corrosion. However, it can also make it vulnerable through flaws in the zinc coating which can release hydrogen bound up in rainwater and fog and drive it into the steel during an electro-chemical reaction. Hydrogen makes hardened steel brittle, leading to stress cracking corrosion.
Issues with combining two different metals
In coastal locations, it is common for metallic corrosion to occur when two dissimilar metals are in ‘electrical’ contact and bridged by an electrically conductive liquid. Seawater or salt laden moist air is more of a risk of producing this conductive liquid. The ‘cell’ produced can result in corrosion to one of the paired metals. This can be an issue when stainless steels are in contact with other metals, depending on the circumstances.
A corrosive cell can result from two metals having differing levels of nobility. The more noble metal (cathode) is protected as the less noble metal (anode) sacrificially corrodes. The further apart the metals are, in terms of relative potentials, the greater the driving force in a cell.
The table below shows the order of nobility of various metals, from least to most.
[table id=8 /]
Galvanised steel in contact with stainless steel is considered to be a corrosion risk in severe marine-type environments.
Corrosion risks with aluminium and stainless steel in contact
As the above nobility table shows, aluminium and stainless steel together is a corrosion risk. Aluminium external fasteners holding stainless steel balustrade together is an unsuitable combination, as there is a practical risk of corrosion. In a marine environment, severe localised pitting corrosion can occur on the aluminium components where un-insulated stainless steel bolts have been used to secure the components in place. This problem can be avoided by using modular balustrade assembled from components which are connected internally – for example, with split-sleeve ferrules – thereby taking the issue of external fixings out of the equation.
Aluminium balustrade and powder coating
With its corrosive-free durability, aluminium balustrade is an ideal option for coastal buildings. Over time, aluminium generates a protective oxide film coating giving excellent resistance to corrosion. Aluminium can also be treated with powder coating, applied electrostatically as a dry powder and baked into a solid state for smooth, even protective coating. The finish is much more durable than conventional paint, which is prone to flaking and cracking, especially in harsh environments. Powder coated aluminium combines well with stainless steel balustrade as the powder coating negates any potential issues caused by their difference in nobility. You can find our more about powder coating options for balustrade here.
Structural glass balustrade – with free-standing glass panels – is also a durable option for coastal locations. It avoids the issue of corrosion and maximises the outlook of a building (e.g. from a balcony) whilst enabling maximum solar penetration to the interior of a property. Glass can also be combined with metal stanchions and toprails – below shows a combination with powder coated aluminium. However, on coastal locations it may need more regular cleaning than other environments to maintain an attractive appearance.
Advice from manufacturers and installers
When specifying balustrade for coastal buildings, always seek advice and assurance from manufacturers regarding the suitability of their products for coastal locations. This includes the installation requirements – if a manufacturer outsources its installation, there is a far greater risk of the corrosion issues outlined above. Manufacturers that have their own installation teams can provide experienced fitters with specialist knowledge about local conditions and their specific demands. For expert advice, please contact Neaco’s technical department on 01653 695721 or fill in an enquiry here