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PREPARATION WORK FOR A TIMBER DECK

how to prepare for timber deck

A timber deck and its supporting structure will be exposed to the weather; therefore it is essential that a suitable type of timber is chosen.

Those timbers that will be in-ground contact should have a Natural Durability rating of 1 or 2 in-ground contact or be preservative treated to H4.

Those timbers that will be above ground should have a Natural Durability rating of 1 or 2 outside above ground or be preservative treated to H3.

Appropriate commercially available species include Blackbutt, Spotted gum, Ironbark, Turpentine, Tallowwood, River red gum, Blue gum, Merbau, Treated pine and Cypress.

Timber Posts

Where possible, timber posts should be placed on stirrups rather than in the ground. The stirrups will provide the required termite barrier to protect the deck and will prevent the deck being a bridge for termites to the house. Even if preservative treated posts are used, a termite barrier is recommended.

Decking profiles

There are a number of decking profiles used. Common varieties are plain, pencil round and reeded. Some decking is supplied with one face having a reeded finish. Despite the urban myths (which always sound very logical), it doesn’t matter whether you fix the reeded face up or down. Your choice will greatly affect the appearance of the deck, but it will not affect the life span of the deck.

Decking Board Spacing

It is important to provide an appropriate spacing between the decking boards. Decking boards (treated or untreated) which are exposed to the weather will take up and lose moisture from or to the atmosphere as the environment around the timber changes on a seasonal basis, even when sealed or coated.

The gap or spacing between the decking boards must be sufficient to accommodate any expansion in the width of the boards. Recommended spacing for decking depends on the width of the boards, whether they are hardwood or softwood and whether they are seasoned or unseasoned at the time of fixing.

Fixings the decking boards to Timber Joists

For a weather exposed deck, all fixings such as bolts and nails should be hot dipped galvanized, stainless steel or similar. Generally speaking, the two nails in a board at any joist should not form a single line with the nails in the other boards on that joist. 

It is best to stagger the nails so that there are two lines of nails along the joist. This lessens the chance of a single line of nails creating (over time) a split in the top surface of the joist. Each of the two nails in a board should be driven at an opposing angle to increase the holding capacity of the nails.

Some decking nails are designed to be fixed so that the nail head remains proud of the surface of the board but in an attractive way. Other nails are designed to be fixed so that the nail head is driven below the surface of the board.

This creates a void in the surface of the board which should be filled with appropriate filler. The filler reduces the moisture collecting in the void and the subsequent staining of the timber that may occur.

To reduce the possibility of splitting, nails should not be too near the edge of the board. Pre drill the board when nailing the ends of the boards to the joists. In most decks there will be some butt joints.

Care should be taken to ensure these butt joints are randomly spaced to avoid butt joints in adjacent boards being next to each other.

There are two methods of protecting the top surface of the joists. A brush on timber preservative can be applied to the top surface of the joists prior to fixing the decking boards to the joists.

Alternatively, an appropriate protective strip can be fixed to the top surface of the joists. Specially made protective strips are available. This lessens the chance of a single line of nails creating (over time) a split in the top surface of the joist.

Each of the two nails in a board should be driven at an opposing angle to increase the holding capacity of the nails. Some decking nails are designed to be fixed so that the nail head remains proud of the surface of the board but in an attractive way.

Other nails are designed to be fixed so that the nail head is driven below the surface of the board. This creates a void in the surface of the board which should be filled with appropriate filler.

The filler reduces the moisture collecting in the void and the subsequent staining of the timber that may occur. To reduce the possibility of splitting, nails should not be too near the edge of the board.

Pre drill the board when nailing the ends of the boards to the joists. In most decks there will be some butt joints.

Care should be taken to ensure these butt joints are randomly spaced to avoid butt joints in adjacent boards being next to each other.

There are two methods of protecting the top surface of the joists. A brush on timber preservative can be applied to the top surface of the joists prior to fixing the decking boards to the joists.

Alternatively, an appropriate protective strip can be fixed to the top surface of the joists. Specially made protective strips are available.