Pressure-treated wood is infused with preservatives to protect it against rot as well as termite infestation. Treated wood is useful in outdoor structures that are consistently exposed the elements, and most wood decks use pressure-treated wood. Although highly resistant to rot, pressure-treated wood can still become cracked because of moisture and heat, or become punctured or gouged. A severely damaged plank should be replaced, but it's easy to patch minimal damage with wood filler.
Remove any loose splinters from the areas to be patched, using a utility knife, a putty knife or sandpaper.
Clean the areas to be patched to remove dirt, residue and stains and to ensure proper adhesion of the wood filler. Use a non-toxic wood cleaner. These cleaners come in a dry concentrate and are oxygen-activated when water is added. Dilute according to the manufacturer's instructions and use a soft-bristle scrub brush to scour the wood. Rinse the deck with fresh water and allow to dry.
Pick up a scoop of the wood filler on the end of a putty knife and work it into the crack or hole. Make sure the crack or hole is completely filled, then scrape the blade of the putty knife flat across the surface of the wood to level off the wood putty.
Clean up any excess wood filler from around the patched area with a damp rag.