Decks come in all shapes and sizes. They’re also built using a variety of materials and for different corrosive environments. As a result, choosing the right fixings for the job can be a difficult task. Not withstanding the applicable Australian building codes and regulations, there are some basic guidelines that can steer you in the right direction when selecting fixings:
1) Choose the right corrosion protection
Don’t risk a costly re-build by choosing the wrong coatings. To ensure a long life from your deck, choose fasteners with the right corrosion coating to match your environment. For dry rural and urban environments that are more than one kilometre from the sea, the minimum recommended coating protection on fasteners is galvanising – either hot-dipped galvanising (dipped in molten zinc) or mechanically coated (with 25 microns of a tin/zinc alloy). Galvanised coatings generally offer a long life for fixings in these conditions. When fixing to or into CCA- and ACQ-treated timbers – like treated pine, for example – in dry rural and urban environments, Climacoat® and Tufcote® coatings will substantially increase the life of the fixings in these treated timbers. Climacoat® and Tufcote® are special coatings that provide protection against galvanic corrosion caused by the chemicals in the treated timber.
Mild coastal environments are generally limited to a distance of one kilometre from the coastline, but can extend many kilometres inland depending on topography and wind speeds. Extreme coastal environments extend from the beachfront to several hundred metres inland. For these corrosive environments, fixings made from austenitic stainless steel material will provide the best protection against corrosion. Stainless steel 302- or 304-grade material is recommended for mild coastal environments and 316-grade material for extreme coastal areas. These stainless steel fixings offer the best corrosion protection in treated timbers in coastal areas.
2) Choose the right fixing
Using Bolts & Nuts
Bolts and nuts can be used when fixing timber bearers to posts, fixing posts to post supports and fixing timber balustrade posts to floor joists. When joining timber to timber or metal, choose a cup head bolt for a smooth finish. The square under-head design will lock the bolt in place and it allows the nut washer combination to tighten without turning the bolt. For metal to timber or metal applications, use a hex head bolt.
In recent times, screws have become more popular. Screwed decking boards don’t ride up over time or leave nail heads protruding. Screws can also form part of the design feature of the finished deck. When using screws to fix decking boards, it is always best to pre-drill and pre-countersink the decking boards. This stops the decking boards from splitting at the joins, or ends, and it sets a consistent depth for the screw head (generally 1-2 mm under the surface). Pre-drilling and pre-countersinking is particularly important when using stainless steel screws. These screws are softer than hardened steel alternatives and need to be driven home at a lower speed to guard against screws snapping during installation.
When fixing common treated pine decking boards (22mm thick) to softwood timber joists, 8- or 10-gauge screws are recommended. When fixing hardwood decking boards or fixing to hardwood joists, 10-gauge screws work best. Bugle Batten screws in a 14-gauge are generally used to fix thicker decking boards and sleepers, and they offer a large head finish that becomes part of the deck design. When choosing the correct screw length, it is recommended that you allow a 25mm minimum embedment into the timber joist. There are different corrosive environments and building materials (many not covered by this article) that will present challenges when building decks. Following the above basic guidelines will assist you in choosing the correct fixings.