A chair is made up of a number of small, relatively weak pieces of wood that all work together to make it strong enough to hold a person. However, if a joint is loose, the overall strength of the chair is weakened-and that single loose joint could lead to another-and soon you'll end up with a useless chair. This is why it's important to you know how to deal with loose chair joints. Here is how.
Remember, the simplest repair may well be the best repair. If a joint on your chair is loose, the easiest way to repair it might be to simply reglue it. Use a glue injector (available at home stores) or a syringe filled with polyurethane glue to inject glue right into the loose joint.
Clamp or hold the joint tightly together overnight, then put the chair back into service. Hopefully the newly glued joint will hold.
Insert some moisture into the joint before injecting the glue, which may help the polyurethane glue hold old dried wood together, since moisture causes polyurethane glue to foam up and expand.
Remove the chair rung and sand the end to remove all traces of old glue in order to repair the joint (if new glue alone isn't strong enough to hold it).
Spread a thin layer of regular wood glue around the end of the rung, then wrap rows of silk thread around the rung to increase its diameter. Finish up by applying a second coating of glue.
Insert the now silk thread-wrapped chair rail into the chair leg and clamp it tightly overnight.
Alternatively, rather than removing the rung and wrapping it with thread, you can try inserting glue-soaked toothpicks into the joint. Leaving them in place, clamp the repaired rung joint and allow it to dry overnight.
Once the glue is dry, simply cut off the protruding toothpicks.
Remove the chair rung and fasten it upright in a vice.
Make a thin cut across the width of the rung, then insert a thin wedge soaked with wood glue into the cut. Be sure the cut in the rung is no deeper than the distance the chair rung goes into the chair leg. Also, be very careful you don't split the chair rung when inserting the wedge.
Allow the wedge to dry, them trim and sand it smooth.
Apply wood glue and insert the newly expanded chair rail into the leg, clamp and allow it to dry overnight.
The expanded chair rung should fill the hole and hold tightly.
Chair legs and rungs can be particularly hard to clamp because they are often odd shapes. As an alternative, you can wrap pieces of cloth (or even rope) around the legs and use a piece of wood or metal twisted like a tourniquet to apply pressure to hold/clamp the glued sections tightly together.
Polyurethane glues are relatively new in the United States, and some store employees may not be familiar with them. Some brand names are "Gorilla Glue" and Elmer's "Ultimate." Polyurethane glue reacts strongly to moisture (even the moisture in your hands), so it can be hazardous to use. Be sure to protect your hands by wearing gloves when using it.