Decks are exposed to the weather and must be protected to remain strong and in good condition.

The surface of all exterior timber will eventually become weathered and discoloured, and even split or crack. Rot and mildew are more serious effects of weathering. To help counteract it, apply a water repellent and a finish coat of oil or paint.

Most water repellents provide limited protection and need to be applied every 6 months or so. The repellent penetrates the surface of the timber without altering its natural colour, although pigments may be added. Other additives, such as ultraviolet stabilisers, insecticide and fungicides, can be incorporated for greater protection.

Especially formulated decking stains or oils can be used for a natural look or to change the colour of the timber. Both stains and oils provide protection for up to 3 years, or even longer depending on the conditions. They are easy to apply and maintain and don't peel, crack or blister like some paints do.

Tips:
Stains will perform better when the surface has had a primer coat of water repellent.

Any paint used should be specially formulated for external timberwork: ordinary house paint will not withstand the constant exposure to the weather. Paint manufacturers make special paint for decking.

Here's how
1 Make sure the timber is dry or the finish may blister or crack. To test, splash a handful of water across the boards. If the water is absorbed by the timber within a few minutes, the timber is dry. However, if the water remains on the surface for some time, the timber is wet and needs time to dry out before finishing. This could take up to a week or more.

2 If the timber has discoloured patches, remove them by sanding or washing the timber down with a timber bleach. To eliminate minor defects such as marks, splintering or rough surfaces, lightly sand the surface and then ensure it is free of dust or oil before finishing. Pressure treated timber may have powdery deposits on the surface. Remove them by lightly washing the surface with mild soap and water.

3 Using a paint brush or roller, apply the finish, keeping an even amount on the surface and working the edges so that they remain wet to avoid a streaky or patchy appearance.

Source: Building Decks (Murdoch Books) Better Homes and Gardens Mini Workbook series $4.25 in newsagents, hardware stores and nurseries.