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Exterior surface coatings play an important role in the final steps of the manufacture or construction and later, in the maintenance and renovation of wooden objects and structures. The performance and the selection of an acceptable finish for an exterior wooden structure or product is influenced by several factors. These include wood characteristics, environmental exposure conditions, durability, cost and maintenance.

There are various types of exterior products available on the South African market and suitable for local conditions.

The function of finishes is to primarily protect outdoor timber against the adverse effects of weathering. At the same time, they should enhance the appearance of the wooden product.

Protection against weathering is obtained by:
- optimal control of the moisture content level variations in timber
- absorption of destructive ultra-violet (UV) radiation
- finding a suitable match between the heat and moisture-induced dimensional changes of the wooden substrate with that of the finish.

Finishes decorate by:
- accentuating wood grain and timber colour
- providing colour by staining, bleaching or obliterating
- modification of the surface texture by smoothing or providing lustre.

Although finishes can keep the moisture content of wood below the levels where growth of wood destroying fungi (rot) in non-preservative treated wood is supported, once these levels are reached, finishes do not have the ability to stop the degradation process. Therefore, due care should be exercised to prevent design and construction defects that cause the unwanted ingress of water in places of structures other than through the finish alone. Once inside wood coated with finishes, excessive moisture can be trapped inside much longer and actually create prolonged favourable conditions for fungal growth.

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