If a deck board is bowed, you'll have to bend it straight before fastening. Some carpenters drive a chisel, pry bar, or awl into the joist and then use it to lever against the board. This method works, but not as well as a purpose-built tool like the BoWrench or the PowerHand.
BoWrench. You use this tool (17) to grasp the top of a joist and pry bowed deck boards into position. It can be a little tricky to set up the first time, and it requires precise positioning so that there's enough throw to lock it off. We've had a BoWrench for about 10 years, and it's worked on every board we've tried it on — even ipe, which is notoriously tough. The tool sees less use than it did when we installed wood decking, but it occasionally comes out when we have to wrangle a badly warped synthetic board. Price:$50. www.cepcotool.com.
PowerHand. I recently began using the Deckmaster PowerHand (18), a device that grasps a joist or adjacent deckboard to push or pull bowed boards into place. It's similar to the BoWrench, but the mechanism is far more advanced and you can use it from a standing position. Price: $205. www.grabberman.com.
Greg DiBernardo owns Fine Home Improvements of Waldwick in Waldwick, N.J.