Why rungs loosen
Rungs, also called stretchers, usually have round tenons glued into drilled sockets in the legs. Over time the glue can fail, and in dry winter air the wood shrinks, so the joint loosens. A loose rung is often a sign that other joints in the chair are loosening too.
Check the whole chair first
Before you start, rock the chair and check each joint. A loose rung often means the whole chair is working loose, and fixing only one rung can lead to repeat failures. How to restore an old chair sets out the full order of work.
Label each part with masking tape as you take it apart, such as front left, back right, or the rung’s position. Note how each rung is rotated, so the chair goes back together the right way round. Then set the chair on a flat, level surface so all four legs touch.
Taking the joint apart
Ease the joint apart with a rubber or dead-blow mallet, tapping gently. Neighboring joints may need loosening too. Don’t force a joint that won’t move, because you can split the wood or break a part. If a joint is solid, leave it alone.
Softening the old glue helps. Hide glue softens with warm water or vinegar, and vinegar won’t work on polyurethane glue or epoxy. PVA glue responds to heat, so gentle heat followed by scraping works better than soaking it.
Cleaning sockets and tenons
Clean the sockets with a scraper, or wrap sandpaper around a dowel and turn it inside the hole. Don’t enlarge the socket. A bigger hole leads to a looser joint. Clean the tenon with fine sandpaper, and keep its shape. A tenon that’s too thin will be loose again.
Gluing and clamping
Apply glue to both surfaces, inside the socket and on the tenon. Work quickly, and don’t use sawdust or matchsticks to fill a gap, because those fills are weak and often fail.
Use a clamp that suits the chair’s shape. Band clamps or a rope tourniquet work well on chairs. Pad the contact points so the clamp doesn’t mark the wood. Keep the chair flat on a level surface while the glue sets, and check that it’s square by measuring the diagonals.
Leave the glue to cure for the time on the label, often overnight, and don’t sit on the chair for about 24 hours.
Snug and slightly loose joints
If the tenon is snug, PVA or hide glue is enough. Hide glue is the choice for antiques, since it can be reversed later by a future restorer.
If the tenon is slightly loose, build up its surface with a thin shaving of wood or a glued-on veneer, then refit it. Gap-filling epoxy can also work on a slightly loose joint, but it isn’t reversible.
Wood-swelling glues, which swell the fibers to tighten a joint without taking it apart, are another option. They can help as a quick fix, but they’re less permanent than a full regluing.
Pins and wedges for extra strength
A small dowel driven through the leg and tenon adds a mechanical lock, so the joint holds even if the glue fails. For a through tenon, a kerf and wedge can lock the joint. Windsor chair legs are often built this way; see how to restore a Windsor chair. Orient the wedge across the grain of the leg, not along it, to avoid splitting the leg.
Wedges are strong, but they’re hard to undo. Think about whether a future restorer may need to take the joint apart before you choose them.
Cure time and safety
Let the glue cure for the time the label gives, and avoid sitting on the chair until it’s had about a day. If you use epoxy, wear gloves, since it’s a skin sensitizer, and work with good ventilation.
For a related leg or frame repair, repairing antique furniture legs covers the hide glue and clamping steps in more detail.