Straight wood is important on a deck because it not only enhances the deck's looks but also helps the deck hold up better in weather over time. While most high-quality wood that is cut for deck construction is straight, cheaper types of wood and boards used to build decks sometimes are bought warped or become warped over time due to weathering. Fortunately, there are ways to straighten these warped boards.
Unfasten the Warped Board
The first step in repairing a warped board or boards in the deck is to unfasten them from the deck itself and then try refastening them through different holes or by different means. Sometimes the wood in the warping board just needs a different area of tension in it to relieve the warp. Try stainless steel galvanized nails or screws when refastening to see if it repairs the warp in the board. When attaching nails or screws, drive their heads a short distance below the surface of the board. If this doesn't repair the warp, then the boards are at least already loose or have been loosened so you can replace them easily.
Another technique for repairing warped boards is by using a chisel to straighten them out. Once the boards have been removed, reaffix them into place by hammering in nails about a quarter of the way, so that they are just about to go through the board and into the wood joint to which the board will be connected. Then take a chisel and line it up against the top of the joint and the base of the warped wood plank. Drive the chisel where those two pieces of wood meet, pressing the warped plank back against the planks on the other side of it. The warped board will often flatten out while the chisel is in there. Now drive the nails down the rest of the way through the board to joint below.
A heavy-duty pipe clamp can also straighten out crooked or warped boards on a deck, though this technique only works if you're letting the boards for the deck run long and will cut them off later. Slip the pipe clamp onto the end of the warped boards and gradually tighten it as you reaffix the boards to the deck by adding nails or screws into different sections. By the time you have added all the nails or screws, the boards should be locked flat into place.