17.2 MRM Fastener Performance Requirements and Testing
Durability testing of construction fasteners for external cladding, suitable for Moderate, Severe, Very Severe, and Extreme Environments.
Typical applications include the fixing of non-ferrous metals, metallic coated steel, and painted steel cladding products to a primary structure. The fasteners may be non-ferrous metal or metallic coated steel.
The outdoor corrosion test site shall be located in a cleared, well-drained area not subjected to shadowing from trees, buildings or structures. The site should not be subjected to direct splash from any water body or industrial pollution sources. If industrial or geothermal influences are present, the level at the site should be <90 μg/m3.
The zinc corrosion rate at the outdoor corrosion test site shall be determined in accordance with ASTM G92 and ISO 9226, using mild steel coupons orientated 45° from the horizontal, facing directly into the prevailing winds and surf.
The test panels must face the same direction as the steel coupons.
A total of 100 screws shall be used for each of the test panel and for the control panel, of which 80 shall be crest fixed and 20 shall be valley-fixed in the configuration shown in 188.8.131.52A Fastener Test Rack. The screws may be of a different style, but all screws shall have identical coatings and sealing washers. Screws shall be power-driven into the test panel at their recommended driving speeds and hole shall not be predrilled.
The cladding used in the test panel shall be standard corrugated profile manufactured from metallic coated steel, pre-painted steel, or non-ferrous metal in accordance with the cladding types the fastener is designed for.
Control panels may be used to assess the compatibility of screws and any accessories with their other building materials or test fastener performance against known benchmarks.
All cladding fasteners must be compatible with the material, suitable for the environment and have a durability equivalent to that of the cladding material. All exposed fasteners must have a minimum durability of Class 4.
Representative samples shall be exposed in a test site in the manner described in 17.2.2 Test Panel Requirements until 5% of samples show red rust on significant surfaces. The corrosion rating of the site (measured in first-year mild steel corrosion rate) and the time to failure will establish the screw class in accordance with the following graph.
Complete fastener assemblies, including washers and profiled washers, as appropriate, shall be tested as a system.
It cannot be assumed that colour match painted screws will perform a well as unpainted. Both painted and unpainted samples are required to be tested concurrently.
The historical performance of fasteners exposed in a given environment over a number of years can be taken as a reliable measure of performance, but confirmatory testing in an approved, monitored location must also be done for validation.
Self-drilling screws which have the shanks and heads produced from the same parent material and undergo the same process and coating do not require the coatings on the shanks to be monitored. Self-drilling screws that have different head and shank material or processing shall require the corrosion resistance of the shank to be monitored as for the head.
The maximum current flow through a sealing washer shall be equal to or below 0.5 × 10-6 A for all thermoset and thermoplastic materials, and shall be tested by the specified procedure in Appendix L. of AS/NZS 3566. Any current flow above this level shall be deemed as not meeting the requirements of this Standard.
Fasteners must not fade at more than twice the rate of fade as the roofing material.
Paint coatings should evenly match that of the cladding in terms of colour, and be reasonably intact after installation with approved screw setting methods. The degree of paint loss during installation will be subject to the fasteners’ visual exposure, but should not exceed 10% of the exposed surface in any circumstance.
Some visual corrosion is acceptable after 10 years exposure, to the degree that it doesn’t affect the integrity of the fastener or the cladding material and appears over less than 10% of the fastener’s surface.