Balustrade Design Guide – Part 4: Materials & Finishes
Balustrade for stairs, mezzanine floors, partitions and barriers involves a wide range of technical and aesthetic considerations. Neaco’s Guide to Balustrade Design is a four-part series which explains each key requirement. Having covered stanchions, handrails and infills in Parts 1- 3, our final part focuses on materials and finishes. This aspect can be very important in determining the lasting visual quality and environmental performance of your balustrade installation.
Timber has become an increasingly rare sight in balustrade specifications. There are a number of good reasons for this. It presents a higher fire risk than metal and is more prone to surface damage which can pose safety issues such as splinters on handrails. Wood also requires ongoing treatment to maintain its visual quality, its comfort to the touch and its ability to prevent absorption of bacteria and control infection. Wood’s decline as a specification has been accelerated by the development of wood-effect solutions (see FINISHES section below).
Mild steel (also known as carbon steel) is defined as having no more than 2 % carbon and no other appreciable alloying element. It is more malleable and cost-effective than stainless steel and is a common specification for internal use. However, it has poor corrosion resistance and should not be used in a corrosive environment unless a protective coating is applied. Galvanised steel is suitable for external use but its plain and rather functional appearance makes it more suitable for industrial settings where aesthetics are not a priority. Aluminium is considerably lighter in weight than mild or galvanised steel yet provides comparable functionality as well as superior performance (please see aluminium section below).
With a natural sheen which can be further enhanced by unidirectional polishing, stainless steel has obvious aesthetic appeal and represents an attractive high-end specification. Its visual quality can be maintained with an occasional washing to remove contaminants. It’s also very durable and hard-wearing in many environments. However, there are two grades – Type 304 and Type 316 – which are suitable for different environments and it is important to consider this with regard to the requirements of your design scheme. Below is a summary of the two grades and their suitability for different environments:
In rural environments, Grade 304 performs well on exposed surfaces but slight discolouration is possible on sheltered surfaces. In urban environment it may be subjected to slight tarnishing. In industrial environments it can provide satisfactory performance when the pollution is less extreme, but for aggressive locations an upgrading is recommended. It is not recommended for marine environments as it can suffer from pitting. Generally speaking, we would advise using Grade 304 for dry internal use only as its condition will remain unaffected by atmospheric factors.
Grade 316 is suitable for typical urban atmospheres, where it suffers little or no tarnishing. It will also perform adequately in most industrial atmospheres, but regular washing would be required to minimise slight tarnishing or staining. It will generally provide reasonable performance in coastal locations but the quality of its finish will need to be maintained by regular washing. Without washing it will suffer a degree of discolouration on long exposure. Grade 316 may be unsuitable for environments where a marine atmosphere is combined with hostile industrial pollution.
With a range of natural advantages and suitability for wide variety of environments, aluminium has become a widely specified material for balustrade. As well as being suitable for internal use, it preforms extremely well in harsh industrial and marine environments due to a number of qualities: it is a non-combustible, non-toxic, inert metal which is completely impermeable and corrosion-free. Aluminium is highly durable – one report suggests it has an infinite lifespan in internal installations and a minimum lifespan of 120 years in external installations. It is 100% recyclable with no downgrading of its properties and very little energy required for re-melting. It can be repeatedly recycled without loss of performance. With modular balustrade solutions, this means that you can replace and recycle components with relative ease and no ongoing maintenance is required, adding further carbon savings to a building’s lifecycle. Aluminium is also lightweight (one third of the weight of steel) to provide easier handling, thereby saving on manpower.
Structural glass balustrade or glass panel infills for balustrade avoid the tarnishing and corrosion in external environments which can be an issue with certain metals. Exterior glass will require occasional washing to maintain aesthetic quality but the primary concern, both internally and externally, is safety. You can find out more about this here. Make sure your manufacturer can demonstrate safety compliance with a recognised glass safety impact test.
Two types of structural glass are commonly specified: monolithic and laminated. Monolithic glass is a single pane whilst laminated glass is two panes with a laminate placed in between to provide stability. Monolithic glass usually requires a thickness of 15mm for a uniformly distributed horizontal line load of 0.74 kN/m and a thickness of 19mm for a load of 1.5 kN/m. Laminated glass usually requires a thickness of 17.5mm for a load of 0.74 kN/m and a thickness of 21.5mm for a load of 1.5 kN/m. These required thicknesses sometimes need to be increased for a number of reasons such as increased height and windloading. It is important to consult the manufacturer regarding the thickness required for your particular scheme.
Monolithic structural glass is much harder to break. However, if it does break the glass will shatter, whereas laminated glass will crack. Unlike laminated structural glass, monolithic structural glass needs to be capped by a toprail. However, this is usually desirable to provide building occupants with comfort to the touch.
Glass can be pre-tested at the factory stage with a heatsoaking process which identifies any imperfections or weaknesses. Their frequency of occurrence is extremely rare (approximately once in every 100,000 tests) but investing in a heatsoaking test provides total peace of mind.
Of the above materials, aluminium provides the most versatility in terms of finishing options. It readily accepts a range of surface finishes including painting, anodising and powder coating. Of these options, we would advise against conventional liquid painting, which will eventually start to flake and crack, especially in external environments.
Anodising is unique to aluminium and enhances its surface in a number of ways. Anodic film is totally impermeable and has exceptional abrasion resistance. It also provides optimal surface coverage, natural sheen and excellent preservation of the original surface texture and design, with no risk of fading or chalking. Anodising can be applied in a natural finish or with colouring to match the design scheme.
Powder coating techniques apply the finish electrostatically as a dry powder which is is then baked at high temperatures – a process which is completed at the factory stage. There are different types of powder coating, each offering different advantages which we have discussed in more detail here. However, all forms of powder coating have common attributes:
Smooth, even surface
Safe and warm to the touch (an ideal quality for handrails)
An extremely durable non-chip finish for maintenance-free installation
Eliminates the time and energy which would be consumed by applying a finish on-site
Powder coating is the most aesthetically versatile option for finishing aluminium. Manufacturing techniques can create any colour, including metallic colours. Advances in powder coating have also enabled manufacturers to reproduce the detailed appearance of natural wood grain, providing the natural beauty timber without the various practical drawbacks. It can also mimic the appearance of an anodised finish.