Dealing with floorboard gaps

Q: What can I do about the cracks between the pine floor boards in my century house? The boards are 1-inch thick by 7 1/2-inches wide, with tongue and groove edges. I want to sand and refinish the floor, but the cracks between boards seem too big to leave as is. Some are a full 1/4-inch wide. Can you suggest a filler such as sawdust and wood glue, or some kind of caulking?

A: I've never seen filler that lasts well in a wood floor because seasonal movement ends up knocking it loose as the boards shrink and swell. As bits of filler break off, the floor looks worse than it did before. I'd be tempted to leave the gaps alone if you can, or rout them out to a consistent width, then fill the enlarged gaps with strips of pine glued in place along one side only. Use a long piece of wood to guide your router along each joint (a sheet of plywood is ideal). A 3/8-inch diameter carbide bit would create a perfect groove. You could cut the filler strips you need on a table saw, then run them through a thickness planer afterwards would make their size absolutely consistent. Also, be sure the strips are slightly taller than they need to be to fill the gaps. That way they’ll all become flush with the floor after sanding. Gluing the strips along one side only allows the floorboards to change shape unhindered. If you glued both sides of each strip cracks would develop in time.