More than a century of blowing snow, dripping rain, and the steady tread of foot traffic had finally taken its toll on the flooring of Ken Brown's porch in Montclair, New Jersey. Despite its well-maintained coat of paint, the old fir decking had become soft and splintered along the exposed edge just above the steps. “It was a real eyesore,” Brown says.
Aesthetics were the least of his problems; this type of damage has to be fixed right away, before moisture reaches the joists and turns them into a breeding ground for rot. Once that happens, the joists themselves have to be replaced, a far more difficult and expensive project.
Replacing porch decking is not a challenging task for any homeowner who's used a circular saw and a table saw, particularly if you have replacement boards milled to the same width as the originals. Just resist the temptation to cut out only the damaged areas. Short patches leave obvious and unsightly seams. Instead, follow the steps of This Old House technical editor Mark Powers, who installed only full-length boards on Brown's porch. The new vertical-grain Douglas fir blends perfectly with the old wood and, if given a coat of paint regularly, should survive at least another hundred years.
Cut the first board
You will need to saw through one board lengthwise to remove it and any damaged neighbors. To keep from cutting the deck joists, set the depth of the saw blade by resting its shoe on the edge of the deck and lowering the blade until it's even with the board's bottom face.
Cut the damaged board
Make the cut in a damaged board that's next to a good one and whose groove faces the other boards that will be replaced. (You can spot the tongues and grooves at the ends of the decking along the front edge of the porch.) Starting at the porch edge, run the saw down the center of the damaged board to avoid hitting nails. Stop when you reach the house wall. Remove the saw and drive a 1—inch demolition chisel into the kerf to split the final few inches.
Pry up the old decking
Using a pry bar and hammer, remove the old wood on both sides of the cut, being careful not to harm the tongue of the undamaged deck board. Once the waste is clear, drive the bar's curved end between the joist and the underside of the next damaged board and pry it up. Start at the edge of the porch and work toward the house until the board pops loose. If necessary, chisel out the end nearest the house, and pull any nails left in the framing. Repeat these steps on the remaining damaged boards. Then scrape clean the exposed tongues and grooves of the old boards with a 5—in—1 tool.
Matching new boards to the old
Vertical—grain Douglas fir is widely used for porch decking because it's fairly rot- and dent-resistant, easy to work, and stable, so it holds paint well. When this porch deck was laid, boards of clear, quartersawn Douglas fir were readily available. These days, the same wood can still be had (though at a much dearer price), but the nominal milling dimensions now are 1x4, 1x6 (3/4 in. by 3½ or 5½ in.), 5/4x4, and 5/4x6 (1 in. by 3½ or 5½ in.). An experienced carpenter can mill the new boards down to size on a table saw, or you can do it yourself. (See Resizing New Floors)
Install the new decking
Prime all the boards' edges and lower faces with fast-drying, oil-based primer to protect them from moisture. Squeeze a bead of polyurethane construction adhesive on all the exposed joists, then place the groove of a replacement board over the tongue of an old deck board and press the new piece into the adhesive. Toenail (pound at an angle) a stainless-steel ring-shark siding nail through the tongue of the new board and into each joist. Recess the nailheads with a nailset and hammer. Continue installing the new decking until you're ready to put in the last piece.
Trim the last board
The last replacement piece cannot be toenailed, so mark the location of each joist on the faces of the neighboring boards. Then cut off the bottom edge of the last board's groove so it can rest on top of the last exposed tongue. To do this, adjust the table saw's blade depth and fence position so this sliver of wood will be lopped off in one pass as you slide the tongue along the fence.
Install the last piece
Tilt the trimmed piece and slide its tongue all the way into the groove of the old decking. Gently tap the groov side into place until it rests on top of the adjacent tongue. Drive the siding nails vertically, down through the face of the new piece and in line with the joist-location marks. Pound the heads below the wood surface with a nailset and fill with putty.
Sand the patch flush
Using 80-grit paper, run a belt sander diagonally across the new boards until they're nearly flush with the old ones. Then, switch to a random-orbit sander with 100-grit paper and smooth away the belt sander scratches. Vacuum up the sawdust, wipe the wood with a tack cloth, and brush on a matching oil-based deck paint.