advises builders and tradespersons to ensure that the steel they buy meets with compliance requirements.
The high Aussie dollar is seeing the entry of a greater number of imported products into the country including light gauge steel products sourced from a range of offshore manufacturers. These products create risk for the building trade in the absence of data about their performance or compliance with Australian Standards.
Many of these products are being used in good faith by trade professionals in the belief that they meet minimal quality requirements for their application, which may lead to inadequate or non-compliant installations.
A good tradesperson wants certainty that all his materials are fit for purpose and comply with Australian Building Codes. There are several factors that impact steel performance, which can be used by builders and tradespersons to assess the quality of this key building material.
Corrosion resistance, mechanical properties and written warranty are three very important considerations when evaluating the quality of steel.
Though all materials eventually deteriorate over time, the speed of deterioration depends on variables such as the environment and product properties. Rust is the most common sign of steel deterioration and is avoided by coating steel products with metallic coatings.
Metallic coatings used on building products include hot dipped zinc/aluminium coating used for steel roofing, wall sheeting or rainwater goods, and hot dipped zinc (galvanised) coating, commonly used for structural steel purlins, steel stud and track sections, steel internal and external corner beads, and steel suspended ceiling components.
The Building Code of Australia (BCA) generally requires products and systems to be ‘fit for purpose’ but it does specify a minimum protective coating for the intended design purpose in Volume 2 of the Code dealing with Class 1 and 10 buildings (Housing Provisions).
The BCA Volume 2 (section 184.108.40.206) states that a minimum steel coating of Z275 or AZ150 is to be used for protection of the steel frame. AZ150 refers to an Aluminium/Zinc coating of 150 grams per m², and Z275 refers to a Zinc coating of 275 grams per m².
Volume 1 of the BCA covers virtually all commercial building types such as hotels, schools, hospitals, restaurants, car parks and office buildings.
The important thing to remember when determining suitability for design is that the life of a zinc coating is directly proportional to its thickness. The zinc will continue to sacrifice itself in order to protect its base metal, so the more zinc there is to start with, the longer the product will last.
However, zinc is about twice the cost of steel with producers likely to reduce the zinc coating thickness to reduce manufacturing costs without affecting the appearance, making it almost impossible for the layman to differentiate.
In fact, manufacturers tend to compensate for the reduced coating thickness with an increased base metal thickness, making the product stronger and appear better in quality, though less corrosion resistant in reality.
What to look out for:
- Look for spangle (glitter or shine) on the surface of the product, indicating it has a metallic coating
- Check the labelling on product or packaging, material specifications or certification
- Beware of ZnO (Zinc Oxide), or ‘white rust’ forming, this means the zinc coating is already starting to sacrifice itself, and may lead to the formation of red rust
- Avoid products with surface damage such as deep gouges, which have penetrated the surface coating, as well as any zinc peel or flaking
Builders take pride in the quality of their work and desire to walk away from each job knowing that the installation and their reputation remain intact. A quality job is the result of using products that physically perform the task required.
For instance, when it comes to the mechanical properties of drywall steel framing, two things to look out for are the guaranteed minimum yield strength, and the base metal thickness (BMT).
Yield strength, expressed in MegaPascals (MPa) is the point to which the steel can be stressed before it deforms permanently and is clearly marked on the product with the letter ‘G’ followed by a number. Higher the number, greater is the structural strength.
BMT refers to the thickness of sheet steel prior to adding the corrosive protection. The Australian Standard (AS/NZS 1365) often refers to minimum BMT to meet differing design purposes. Material grade or thickness can have a dramatic effect on performance.
Often the BMT will be less than expected due to its coating. For example, a 0.50mm BMT product with a Z275 coating is approximately 8% thicker than an uncoated equivalent, and has a Total Coated Thickness (TCT) of 0.54mm.
What to look out for:
Quality and consistency, guaranteed
- Most manufactured drywall products have a clear marking stating both Grade and BMT
- Cheap prices may be an indicator of lower gauge, grade or zinc coating
- Buy from a reputed manufacturer who can supply the product with a comprehensive written warranty
Ensure that the manufacturer has a robust quality control system such as ISO9001 or equivalent, and regularly tests the performance of their products to meet exact specifications. This should be backed up with a quality guarantee in writing.
It is also important to avoid mixing systems as it is critical not only for maintaining the system warranty, but also for safety. Not all products are manufactured to the same specifications and this can mean inconsistencies when swapping products. This is especially important when it comes to suspended ceilings, where system collapse could lead to devastating consequences.
Rondo is a specialist supplier of ceiling systems and wall systems such as suspended ceilings, steel stud partition walls, plaster and render finishing sections, and wall and ceiling access panels.