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Design for Durability -
Corrosion Resistance of Fasteners
The interaction of
moisture and chemicals on metals can cause breakdown of
wood fibres around metal fasteners. This breakdown can
result in additional moisture traps and loosening of
joints with a propensity for decay.
To prevent deterioration
of timber around metal (particularly fasteners) where
moisture is present, the following can be employed:
- metal fasteners
should be detailed using material with the
required resistance to corrosion. Table 1
provides a general guide to the selection of
metals with appropriate levels of corrosion
resistance
- countersink and plug
or stop fasteners (prevents moisture traps)
- avoid the use of
dissimilar metal for fasteners
- grease, coat or
sheath fasteners in contact with CCA treated
timber.
Reference: Timber Datafile
P4 – Timber – Design for Durability of the NAFI
Timber Manual.
Table 1 Selecting
Corrosive Resistant Fasteners
| Material |
Applications |
Remarks |
| Stainless steel 304 |
Chemical, industrial,
marine |
Grade 316 is preferred for
marine environments. Additional protection via
coatings should be applied to 304. |
| Monel |
Marine |
Usually used in boat
building, nails & screws available. |
| Silicon bronze, copper and
brass |
Marine |
Usually used in boat
building, nails and screws available. Do not
bring in contact with aluminium. Silicon bronze
nails are also available for acidic species, e.g.
western red cedar. |
| Hot dipped galvanised and
mechanically plated |
External exposed to weather
and medium corrosivity. Industrial and marine
environments. |
Where in contact with moist
CCA treated timber, additional protection using
plastic sheaths or bituminous epoxy coatings are
suggested. |
| Plated (zinc, cadmium) and
gold passified. |
Internal exposed to view or
protected from the weather and corrosive
environments. |
Care required with handling
and installation to avoid damage of the
protective coating. |
| Mild steel |
Fully protected from the
weather, moisture or corrosive gases. |
Use zinc dust paint systems
to provide a base for conventional paints. |
Note: 1. The metals/coatings described
are in descending order of resistance to corrosion.
2. Life expectancy of zinc coatings is
determined primarily by their weight or thickness. As a
minimum, hot dipped galvanised fasteners should have a
coating thickness of 42 microns. Refer to AS1214.
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