DIY Advice Needed on Repairing Damaged Staircase Stringer in Home

I’m pretty competent as a DIYer, but unsure how to tackle a cracked INNER staircase stringer in our rental house. These are simple box stairs. The stringer on one side has a 30-inch crack in it. This image shows the worst of it, but when you look at it from above, it doesn’t look nearly this bad. Most of the crack is very narrow, about 1/8 to 1/16 of an inch. I think the crack developed over many years. No idea if it’s getting longer. Yes, Nor Abram would replace the stringer, but that’s a huge job. Tommy SIlva might use a series of steel straps to stabilize the crack, then glue and seal it. Problem is, the underside of the stairs is sealed drywall, so accessing it would be messy.

We will be selling this house in a couple years, so I’m considering injecting a strong carpenter’s glue or epoxy into the crack, then covering it with wood filler, then priming and painting. Another idea: Given how narrow most of the crack is, I thought about drilling small holes along the crack so that I can inject more glue into it, but I could see that backfiring. I don’t see any way of clamping the wood while the glue dries.

Your suggestions are greatly appreciated.

Am trying to upload photo but keep getting message that embedding media isn’t allowed.

Post it on a free photo hosting site and post the link here.

Gotta go to Imgur or one of those places. I can’t do it either.

I’m gonna say, without seeing the crack, if it’s been there umpteen years I would glue if you think necessary. And then carpet.

I know that’s cheating. If there’s no danger the stair case will fail. Cover and forget.

It’s the “inside stringer,” above the carpeting. I think I could glue, patch, sand, and paint and make it completely disappear. The staircase seems very stable. But a patch job does feel like cheating. :zipper_mouth_face:

That said, I’ve often heard that a good glue (Gorilla or Loctite) will bond the wood so well that the glued seam will be stronger than the surrounding wood.

Oh. I see.

That is true. IF you can inject the glue so the entire cracked area is glued.

Conversely, if instead you all-but caulk over the face of the crack with a smidgen of glue leaving the actual crack unchanged, you’ve accomplished nothing. There is no good way I know of to drive glue into a very thin crack as we see in your pic.

Amazon sells glue syringes of various sizes, but in the really thin cracks, I can’t see this working very well. The idea of opening the crack up winder so that I can inject more glue strikes me as risky.

I think this is one of those situations where I do my best and hope for the best.

As far as glue, I would consider epoxy – it will harden and fill the gaps better than wood glue. You can get a glue syringe to force it at least partway in. Bear in mind that if that crack isn’t brand new, there is almost certainly some amount of dust and dirt in that crack, and that will work against adhesion. Work the epoxy in to the crack with thin-bladed knives or flat probes* and don’t be afraid to put plenty in there. Just be prepared to wipe up the squeeze-out, if you’re lucky enough to get any, before it sets up. If you haven’t done so already, I would use probes to see if I can tell how deep the crack is.

For clamps, I’ve never seen this exactly, but I can imagine a device that you could screw deeply into the stringer on either side of the crack, with a turnbuckle to bring the sides together at least a little.

*To see this in action, watch the furniture repair videos of Thomas Johnson Antique Furniture Restoration on YouTube. He has cracks to repair in lots of his videos, and although he usually is able to apply clamping pressure, you can see him working the glue into the cracks. He only uses epoxy when it’s a bad joint or he isn’t able to close it completely, but it will give you the idea.

Great information, thanks!

I have treated similar cracks by diluting carpenters glue about 1:1 with water, and using a disposable syringe with a medium thin needle to inject the mixture deep into the cracks. From what I can see in your picture you should be able to fill the crack from the inside out with this method. There will be run-out glue so have a rag at hand, and possibly use masking tape on the stair carpet as well. @Roderick_Femm makes a good point that any dust or crud in the crack can affect the bond, so if you have a can of compressed air you should try using it to clean the crack as best as you can first.

Another thing you could try is to apply two or three pocket screws per “section” starting an inch or so above the crack. This would require buying the jig to drill the holes, so if it’s a one time job may not be affordable. Getting the drill jig in between the stair and riser and the underside of the baluster might be tricky.

Those “stronger than the wood” claims only apply to a tight joint. In addition to the cleanliness issues already discussed, be aware that polyurethane Gorilla glue has no ability to bridge gaps. It just expands into a crunchy and useless foam. PVA wood or carpenters glue isn’t a lot better. Epoxy, on the other hand, will make a structural bond across a gap, but as you’re already aware, you really have to get it in there.

I like @moes_lotion’s pocket screw idea.

I’m not sure what the minimums are for housed stringers, but a notched stringer is (typically) allowed to have a 5” minimum throat. As such, you probably have enough material below the crack that this isn’t a structural concern. On the other hand, if this crack wasn’t there when you bought it, it happened for a reason. (If it was always there, it could’ve been a drying crack and not be an issue, as long as the material below the crack was wide enough)

Very helpful information. I reinspected the crack. Most places, it’s too narrow to get anything in there, even dilute glue – but I will still TRY. In wider sections (see photo), I could get some epoxy in there using a wafer-thin artist’s palette knife or similar, kinda of wedging it in there. Epoxy sets fast, so I’d need to work fast and make it in two batches. JB Weld has a wood epoxy. Perhaps that?

Here is a photo of the underside of the stairs in the basement, which are identical. This ain’t old-school Yankee craftsmanship, boys. Again, I CANNOT access the underside of the 2nd floor staircase.

I do have a Kreg tool, the small intro one. Not sure where I’d clamp it in place, but I can figure it out. The stringer is not real thick, so I’d have to be careful.

I lived at the house before I rented it out. One day I had some big friends carry a solid-oak entertainment center upstairs. It easily weighed 225+ lbs. and these two guys were 225# each. I remember them struggling to lift it overhead and carry it up the stairs. Maybe that stressed an existing hairline crack.

A combination of glue and pocket screws should do the job. Just the pocket screws may be sufficient to keep the crack from expanding but glue will make it stronger and the pocket screws should provide some clamping action. Epoxy makes the most sense here because even penetrating the crack by 1/4" will strengthen the joint, fill the gap and can be sanded down to a smooth surface to repaint. You can dig out the wood along the crack so more glue can be contained. I don’t think I’d try to pry the crack open though. Just use tape to mask above and below the crack so you don’t have a ton of glue to sand down when done.

It doesn’t look that bad really, if it’s not creaking and moving you may not need to do anything right away. If you pull back the carpeting you might see that the treads are holding the stringer together and it only needs cosmetic work.

I’m a little surprised by the thickness of the stringer in your basement stairs picture. I’d expect at least a 2" thickness, but yours looks thinner. If the same lumber is used for the cracking staircase then you’re right about possibly ending up with the pocket screws poking out the other side of the stringer.

Can you tell the average depth of the crack by probing with a fine needle or thin bit of wire? If it is currently no more than 1/8 to 1/4 inch deep then the structural integrity is not going to be reduced enough to worry about. In that case I’d just leave it as is, but check back every couple of months.

Another option might be to run some structural screws straight down into the stringer and plug the countersunk holes, although if it’s only a 1x stringer that could be tough. Repairing drywall is not that big a deal–the real solution is a plywood gusset from underneath.

I just measured the depth of the crack – taking readings in two places, where the crack is widest, which turns out to be near where the riser meets the tread, on two contiguous steps. I managed to wiggle a tiny knife blade inside these two cracks, and insert it all the way in, about 1.5 inches, meaning the stringer is cracked all the way through at those two points. Again, other parts of the 3-foot-long crack are very narrow and the depth of the crack is probably shallow. I will confirm that tomorrow.

Glue wouldn’t stick to that painted wood.

The crack needs to be cleaned out with a gouge chisel. Glue the opened crack, and then fill with paintable, plastic wood filler. The chiseling doesn’t have to be precise. Your only trying to get a clean wood surface for gluing.

The width of the chisel is enough and go maybe 1/4" deep. That’s enough to get down to clean wood for gluing.

The crack doesn’t look that serious. I’d try chiseling and gluing. A sharp gouge chisel would clean out that painted crack in a few minutes. Don’t go too deep and weaken the stringer.

Fitting a strip of wood would be stronger. Instead of relying totally on wood filler. But a tedious job on a long crack.

It would be a huge pain in the ass, but I would rout out a pocket along the crack and then screw a metal mending plate across the two pieces, then fill with epoxy wood filler.