Chairs suffer more stress, strain and mistreatment than any other type of furniture, considering their lightweight construction and the heavy load they carry. There are, however, several methods you can use if they have to be repaired:
Straight-chair construction falls into two basic categories: frame or platform.
A frame chair is composed of flat pieces that form a frame that supports the seat. It has two continuous back posts that serve both as the rear legs and the sides of the backrest.
A platform chair has round legs, rungs and spindles. It has a separate back assembly that fits into a seat and the seat is supported directly by the legs. The joints that hold the platform chair together are mostly all dowel joints--the round legs, rungs and spindles fit into holes in the seat and legs.
All but the finest straight chairs can often be repaired at home with simple tools. The repairs depend in part on how the chair is constructed. Frame chairs, for example, are prone to break at the joints near the back of the seat. In platform chairs, the joints between the rungs and the legs are most vulnerable.
Before You Start
Before taking a chair apart, examine it. Plan to correct any previous quick-fix repairs. Before disassembly, remove all the fasteners. Label the components to ensure correct reassembly.
In any chair, the best way to fix a loose joint is to dismantle only the affected parts and reglue them. To dismantle a joint, gently work the pieces loose by hand, or use a rubber mallet or a hammer with a padded wooden block. If a joint is only slightly loose, you may be able to fix it by injecting a liquid wood sweller into it. Leave tight joints undisturbed.
Never substitute screws, nails, metal plates or angle irons for a good glue job. It helps to place a chair in a warm, dry room for a few days before dismantling it.
A chair part may work loose because the glue has dried out, the wood has shrunk or because damage to another part of the chair has put a strain on the joint. Many loose joints can be repaired by pulling the joint apart, removing the old glue, applying new glue and clamping the pieces. After the glue is removed, test-fit the pieces without glue to make sure all joints fit properly.
Sometimes the tenon on the end of a rung or spindle needs to be enlarged to fit snugly in its hole. Try wrapping thread or a wood shaving around the tenon, using glue to hold it in place.
If you notice play in a frame chair during use, check to see whether the frame is working loose around the seat. If it is, strengthen the frame by installing glue blocks. Cut a triangular block of hardwood, about 1 1/2 inches thick, to fit snugly into each corner of the frame.
Make the block about 5 to 6 inches long and drill two holes through it and into the frame. Glue the mating surfaces and screw the blocks into place. If the frame already has glue blocks, reinstall them with fresh glue and slightly larger diameter screws to increase their holding power.
Clamp and Glue Tips
Most repairs require gluing and clamping. You can, though, overdo both. Use too much glue and you'll not only create a mess, but weaken the joint or connection by creating a thick, easy-to-break glue line. Aim for a thin, even glue line.
Likewise, don't overtighten clamps. You can drive too much glue out, creating a starved joint. Or you can compress the wood so much that when the clamps are removed and the fibers spring back into shape, they weaken the repair.