TONGUE-AND-GROOVE REPAIRS
To replace damaged strip flooring, begin by marking the boards you plan to remove. Check under a radiator pipe or the edge of a door sill to determine the depth of the flooring, then set a circular saw to that thickness. Taking care not to cut into the joists or subfloor, make two parallel cuts into the board along its entire length, starting and finishing as close as possible to the ends. This will produce three narrow boards; the middle one will come out easily with a prybar. The groove side will need a bit of coaxing, and you may have to remove the nails from the tongue side to free it.
Cut the new boards to exactly fit each row of your opening, staggering lengths so that the new pattern won’t be obvious. To lace in the new boards, first try using a mallet to persuade the boards to fit into place. Cut away the bottom shoulder of the groove on the side of the board receiving the new strip. Then slide the tongue on the opposite side of the board into the exposed groove on the mating floorboard.
If the tongue still won’t go in, choose a new board and cut the shoulder off the tongue side at a 45-degree angle, including the tongue. Fit the detached shoulder with its tongue into the groove on the adjacent board. Then nose the rest of the patch board into the mating tongue on the opposite side. Make adjustments as needed to get the board to lie flat. Then either face-nail the board in place with finishing nails or glue the new board to the detached shoulder.