Lay the wood out on a concrete patio or driveway. Use a pressure washer, or high pressure hose nozzle to wash the surface of the wood thoroughly to remove dirt, pests, spider webs and other debris. Use a long handled stiff nylon scrubber to remove stubborn dirt. Turn the wood over and wash both sides. Allow it to dry in the sun.
Inspect the wood for split, rotted or damaged sections. Cut damaged sections out with a circular saw to leave sound lengths of lumber. Remove rotted material one inch back into solid material so that the rot does not spread or attract pests such as termites.
Use a claw hammer, nail bar and locking pliers to remove all old nails, screws and staples. Cut off sections or mark with a permanent marker to indicate areas where broken nails and screws could not be removed. Do not cut through these areas with power saws to prevent breaking blades.
Belt sand all faces of your recycled wood with a 100-grit sanding belt to remove oxidation and rough areas, including splinters. Inspect the lumber more closely as you sand, looking for small cracks and splits indicating weaknesses that you may have missed earlier. Dispose of pieces that appear to be structurally unsound.
Stack your lumber with perpendicular skids between each layer, every 24 inches. Stack long pieces on the bottom and shorter pieces above for easy access. Separate wood by length and size, if there is enough material, to save time later in looking through it.
Cut, work and fasten your recycled lumber just as you would new lumber from the lumber yard. Look for weaknesses and old fasteners when cutting, especially when cutting structural support pieces. Dispose of any piece that may not be safe. Remember: You got it for free, so replace what needs replacing.