Q: How do I repair a deck joist that is starting to rot?
A: The easiest way is to repair a joist is to install a sister joist to strengthen the damaged area. Use a hammer and chisel to chip away the damaged wood. Liberally apply two coats of waterproof sealer over the damaged joist. Cut a reinforcing sister joist from lumber that is the same dimension as the damaged joist. Treat all sides of the new joist with the sealer, and face-nail it flush over the old joist with 10d nails or screws every 2 feet. Toe-nail the ends of the sister joist to the ledger and rim joist.