Characteristics of Treated Lumber
Pressure-treated wood has been infused with chemicals to make it more resistant to deterioration and insect infestation. It comes in the form of boards, posts and plywood. Treated lumber usually has been treated with amine copper quat (ACQ) and copper azone (CA), which are less toxic alternatives to the chemicals used when treated lumber was originally developed, but caution should be used when handling it. The Natural Handyman suggests wearing a mask and eye protection when working with treated lumber.
What Type of Nails to Use
The Natural Handyman recommends using galvanized screws or nails that are specially made for treated lumber, especially if it is outdoors, to prevent rusting and deterioration of the nail. If you need extra support or reinforcement for your project, use galvanized metal brackets as well. Treated lumber can be extremely hard, and you should pre-drill the nail or screw holes, keeping them about an inch from the ends of the boards to prevent any splitting while drilling or from the wood drying out as it gets older and is exposed to the elements.
If using the treated lumber for a deck, install it with the bark side up, since it will cup as it dries out. You can see the bark side by looking at the end grain of the board.
When laying a deck floor, there should not be any spacing between boards, since the wood will shrink even if it is treated with a preservative.
Deck posts should be made from treated lumber, as it will not rot due to exposure to cold and moisture when buried in the ground. There may be regulations against burying treated posts for mailboxes or decks, and you should check with your local building inspector before starting your project. Some cities require you to use a concrete footing for posts exposed at ground level.