Nails
Nails can be used for timber to timber fixing, metal connector to timber fixing and plywood or other sheet material to timber fixing.
For economy and performance, small diameter fastenings, such as nails, are used instead of large diameter bolts and bolted connector joints in large and small timber structures.
The development of powered nail-driving tools has meant nails are the typical fixing used for domestic structures and has contributed to a trend towards using steel or plywood plates with multiple fasteners to connect large timber members.
Availability
Nails are available throughout New Zealand from building supply stores.
There are several New Zealand manufacturers and importers of nails.
Most manufacturers can custom-make nails to suit particular requirements, provided that a minimum order is placed, usually about 100 kg.
Key points
- Timber connections are a large and complex part of designing in timber.
- A wide range of fixings are available.
- Selection of the fixing depends on factors such as the environment it will be used in, loading, aesthetic requirements and constructability.
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Nails
Finishes
Steel wire nails
Steel wire nails are available either ‘bright’ (uncoated) or with a corrosion-resistant coating.
Zinc is the most common form of protection and can be applied by tumbling barrels (electroplating or zinc plating) or by hot dip galvanising.
Zinc electroplating produces a thinner, more uniform and smoother coating than hot dip galvanising, but, because of its reduced thickness, it also provides less resistance to corrosion.
The hot dip galvanising process results in a much larger variation in the finished diameter of the nail compared with bright or zinc-plated nails.
Other forms of coatings are available, including resins and cement, and these can be used for particular environmental situations.
Coatings that make the fasteners corrosion resistant can also influence the performance of the joints made with them.
Stainless steel nails
Stainless steel nails are appropriate for highly corrosive environments.
They are available in a wide range of engineered grades, each with its own designation number and specific properties.
Only a few grades are suitable for fasteners – these being those that can be ‘cold headed’ easily and have adequate torsion and shear strengths.
- The 300 series stainless steel nails are the most popular:18-8 grades contain very little carbon, about 18 percent chromium and 8 percent nickel – giving them good corrosion resistance
- 304 stainless steel is not much better than the 18-8 grade with regard to corrosion resistance.
- 316 stainless steel contains molybdenum, which significantly increases corrosion resistance, strength and cost.
Stainless steel should be used with caution in situations below water because they will corrode in an anaerobic environment.
If the fastener is immersed in still water without oxygen, the corrosion-resistant film of chromium oxide will not form, and, without this, the stainless steel nail will suffer from galvanic corrosion and eventual failure.
Other metals
Silicon bronze fasteners are used primarily for marine boat building, but also have an attractive appearance when used with timber panelling because they eventually blend into the colour of the wood.
Silicon bronze fasteners provide excellent corrosion resistance but are soft and require a carefully sized pilot hole to avoid breakage. Copper nails are also available.
