Q: There is a problem in the heavily trafficked, upstairs stairwell of our 1919 house. One of the floorboards (not original to the house) is splitting. A long, narrow portion is pulling away from the main board and is rising up and threatening to come off. My inclination is to hold that portion down and fill the crevices with wood glue, but I’m sure I’d do a messy job. What do you suggest?

A: Wood glue is often a great way to join two pieces of wood, but it probably won’t work in this case. Because the wood is splintering and moving up and down, there is probably not a clean break. You need two surfaces that mate fairly well for glue to hold. And you need to clamp the pieces together while the glue cures, which is difficult in a case like this, though perhaps it’s possible using thin wire nails and weights, such as heavy books.

Although you note that the split piece isn’t original to the house, it’s not clear whether all of the flooring in the stairwell was changed, or whether the broken piece was put in to replace an earlier piece that was damaged or stained. If just that board was replaced, the way it was installed could explain why the edge is splitting off. The original piece would have been cut or chiseled out. Then, to get the replacement piece to mate with pieces on either side, the bottom lip on the groove side would have been cut away, so the piece would lie flat after the edge with the tongue was angled down into the adjoining piece’s groove. This would have left the groove edge of the new piece just resting on the tongue of the adjoining piece, making it prone to splitting loose as the flooring flexed from people walking over it.

There are two basic approaches to fixing the problem: Replace the piece of board with the split, or pull out the loose part and fill the gap with epoxy.

A reader wants to fix this floorboard. Because it’s splintering and moving up and down, wood glue probably won’t work. (Reader photo via The Washington Post)

Replacing the piece will result in a floor that looks good as new, especially if you find a replacement wood that’s the same species and has grain lines that closely match those in the surrounding flooring. Many homes built in the early 1900s, especially on upper stories, have fir flooring that came from trees in the West’s old-growth forests. The grain is straight and tight, with narrow, alternating bands of light and dark wood, marking the decades of spring and summer seasons when the trees grew. New fir flooring will probably have much wider growth lines, so you might want to search for replacement wood at a store that specializes in salvaged building materials.

The most challenging part of replacing a broken floorboard is removing the damaged piece. One way calls for drilling through the floor between floor joists with a wide spade bit and making plunge cuts with a circular saw between the holes to create narrow strips that you can pull out. Then, with a chisel, you can pry or break out the rest of the piece, leaving a clean opening for the new insert. Family Handyman has a good how-to, which you can find by searching “patch a hardwood floor” on familyhandyman.com.

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Or, even simpler if you have the right equipment, you can cut out the old piece with an oscillating multi-tool, such as the Fein MultiMaster. Learn more about this approach by searching oldhouseonline.com for “simple wood-floor fixes.” However you remove the old piece, prep the replacement board by cutting off the bottom of the groove edge. This is most easily done with a table saw. If you don’t have one, perhaps a friend does. Of course, you could hire anyone who repairs wood floors to do the whole job.

Or, if you just want to remove the safety hazard and don’t care if a patch shows, you can remove the splinter, sand off any rough bits that project above the surface and fill the gap with epoxy.

Some epoxies are very thin. For this, you need something you can mix to a moldable, putty-like consistency, such as Abatron WoodEpox Wood Replacement Compound. A 12-ounce kit, with 6 ounces each of Part A and Part B, is $27 at Ace Hardware. WoodEpox dries to a light tan color unless you add powdered pigment when you mix the components. A half-ounce of Abatron’s black pigment is $9 at Ace; the website lists the same price for a 1-ounce container of brown pigment. (The containers are the same size, but the pigments weigh different amounts.) Although not essential, it’s a good idea to also get LiquidWood, another Abatron product, to use as a primer before you apply the epoxy. A kit with six ounces of Part A and six ounces of Part B is $26.24 on Amazon. LiquidWood helps the epoxy bond better and, because it remains slightly flexible over time, it helps the patch stay in place as the wood flexes, said Richard Ahlstrom, Abatron’s sales manager.

To avoid getting epoxy on the surrounding wood, carefully mask off areas just beyond the patch, using painter’s tape (usually called “blue tape”), which won’t lift the finish from the surrounding flooring. Brush on the LiquidWood, if you’re using it. When it’s slightly tacky, put on rubber gloves and mix equal amounts of the two epoxy components, and stir in pigment to get the color you want. The color won’t change much as the epoxy dries, Ahlstrom said.

You will have about 20 minutes of open time. Press the mixture into the crack with a putty knife and level the surface. Don’t overfill, because the epoxy won’t shrink as it hardens. Once it cures — generally in one to three hours — touch up the surface with sandpaper, as needed, taking care not to sand the surrounding wood. If the sandpaper gums up, give the epoxy more time to cure before sanding more. Cure time depends on temperature, which is partly affected by how much you mix at once, because the curing process itself creates heat.

If you want the patch to blend in even better, get an artist brush and paint contrasting lines across the epoxy to simulate grain lines in wood. Ahlstrom said some people even lightly comb the epoxy before it cures, to simulate the texture of wood. It’s art, not science, at that point, he said.