Q: I have an old stairway with several broken wood balusters. How do I replace them?
—S. Christopher Hunter, Ypsilanti, MIch.
David Raymond, owner, Raymond Design Builders, replies: A stair with missing balusters is not only unsafe, particularly for children, it's about as attractive as a hockey goalie's grin. Fortunately, replacing them is fairly easy for anyone who can use a miter saw. It just requires some advance work.
First, you have to find new balusters that match your existing ones. It's unlikely that a home center will have what you need, but companies that specialize in building stairs or making stair parts, such as Harmonson Stairs, can often turn an identical one for you on a lathe. You'll need to supply a sample or two, intact if possible. For paint- grade work, maple is ideal because it's strong and smooth. For stain-grade balusters, ask the company to match the species, too.
Finish the new balusters before you install them, either with paint or polyurethane, then follow these steps to get your stairway back in shape.
Scope Out the Situation
On this stair, each baluster has a tenon on its lower end that fits into the tread. A cap nailed to the end of the tread holds the tenon in place. Finishing nails secure the baluster's top end to the handrail. (On other stairs, these details may vary.) Each baluster on a tread is a different length, so provide the company making the new balusters with a sample of each length.
Remove the End Cap
Whether removing an intact baluster or replacing a missing one, first pry the end cap off the tread. If taking out a baluster, pull it sideways out of the mortise in the tread, then free the top end by tapping it with a hammer toward the top of the stair. Use nippers to pull out any nails in the handrail and tread, and 80-grit sandpaper to smooth the tread around the mortise and the underside of the handrail.
Measure the Length
Custom balusters are made long so that they can be trimmed to fit. First, measure the upstairs side of an existing baluster, from the tread up to where it touches the handrail. Hook the tape measure on the bottom edge of the new baluster—not on the tenon—and transfer that measurement to its upstairs side.
Find the Top Angle
Hold a sliding T-bevel against the upstairs side of an existing baluster, pivot its blade against the underside of the handrail, and tighten its nut to lock the blade. To transfer this angle to the new baluster, hold the T-bevel against the new baluster so that the blade is beside the mark made in Step 3; use the blade's edge to mark the cutline.
Cut to Length
Using the T-bevel, set the angle of the miter-saw blade, then cut the baluster just next to the cutline. Test-fit the new baluster; it should sit flat on the tread when the tenon is in the mortise and have equal spacing between it and the tops of the neighboring balusters. If they're not, shave the top with the miter saw or a swipe or two of a block plane.
Fit the New Baluster
Drill two 1/16-inch pilot holes into, and square to, the baluster's angled end and out the upstairs side. Coat that end with wood glue, fit the baluster into its tenon, and drive 6d finishing nails up through the pilot holes and into the handrail. Set the nailheads with a nailset and cover with putty. Nail the end cap back onto the tread.