A gentler approach to fixing your wobbly legs

Posted on 9th July 2020

By David Edwards, Graduate Diploma Conservation Studies: Furniture and Related Objects

Repairing loose joints in chairs is bread and butter work for furniture conservators. Chairs are particularly susceptible to tension and racking in all joints, but particularly those joining seat frame and legs. Constant stress and overloading of mortice and tenon joints from pulling out and replacing chairs from tables, the shifting of heavy human frames and even (heaven forfend) occasional rocking on the back legs, can cause loosening and eventual failure of joints.

Loose chair leg joints are therefore a common problem. A common solution is to dismantle the joint in order to clean the joint of degraded glue and to allow the conservator to check for the soundness of the timber around the joint. When dismantled, the joint can be cleaned and prepared for new adhesive bonding and thin strips of veneer can be introduced, if required, to compensate for losses or gaps caused by compression within the joint.

However, dismantling the joint should not be considered the only and default option. There may be good reasons to try avoid taking the joint apart. The loose joint may be the only one loose and others around it may be sound and in no need of disturbance. Fragile decorative surfaces on the chair may be damaged by dismantling. And finally significant damage can be done trying to dismantle loose but stubbornly fixed joints, where other elements such as pegs, screws and nails are holding the joint together as well as glue.

It is this last scenario that presented itself in the case of the conservation of a set of 6 mid-19th century oak rush-seated country chairs. These are handsome, well-built, originally sturdy chairs with unusual reeded, curved and crossed splats. Their condition is relatively good, but all of the chairs suffered from loose leg to seat frame joints in both front and back legs. As well as glue, the joints are secured with oak pegs through all of the tenons, so the joints, even when loose, are secure and unlikely to fail completely.

Fig 1. Diagram showing construction of pegged through mortice and tenon

Fig 2. Oak pegs visible in the back leg to seat frame joint

The treatment approach taken for the first chair was to completely dismantle the leg to seat frame joints, clean these and re-assemble the chair, gluing with hot animal glue. The dismantling was not straightforward due to the pegged through mortice and tenon joints. A lot of time and effort was spent working these loose, drilling out the pegs in most cases and damage occurred in one of the joints due to the dismantling process itself. The treatment was eventually completed successfully on this first chair, including repair to the damage done during dismantling but it was clear that a different approach would be needed for the other chairs in the set.

The revised treatment approach required no dismantling of the chairs at all and was significantly less interventive. For each chair the loose joints were carefully identified by working around each joint and attempting to move it carefully. All of the loose joints were in the front seat frame to front leg joint and rear seat frame to back leg joint. All were mortice and tenon pegged through joints, and almost all were loose to greater or lesser extent. Small diameter holes were carefully drilled at 45 degrees into the underside of the seat frame on either side of the leg directed towards the cavity between tenon and mortice in the joint. The objective was to drill alongside the cheek of the tenon. It was generally quite easy to feel once the drill bit had pierced through into the cavity and with practice the holes became more accurate and effective. Next a slighter larger drill bit was selected and used to drill down 2-3 mm into each of the same holes at the same angle.

Fig 3. Drilling at 45 degrees into the joint cavity

Fig 4. Diagram showing direction of drill holes for glue either side of the tenon

This wider opening was created to allow the end of a small plastic syringe to be inserted and used to inject fish glue into the joint. This glue was selected because a cold set collagen glue was expected to provide the best chance of getting good injection and distribution into all areas of the joint. Injection of the glue with a hypodermic needle was originally tried in order to try and minimise the diameter of the drilled holes, however in practice it was hard to get enough glue flowing through the needle and into the joint. Therefore the slightly enlarged hole and direct insertion of the plastic end of the syringe was deemed to be the preferred approach. Once the glue had been injected, the loose joint was manipulated back and forth to ensure that glue penetrated into as many areas of the joint as possible. The joints were then clamped and cleaned of residual glue. Once the glue had dried, all of the holes were plugged with oak plugs which were then trimmed and colour matched. These being on the underside of the seat frame, were not obtrusive at all once the finishing had been completed.

Fig 5. Injecting glue using a syringe into the joint cavity

Fig 6. Chair clamped up after glue injection

The result of the revised approach was very successful. The chairs are once again solid and sturdy with no racking and movement in the joints. No additional damage has been caused through unnecessary dismantling and the plugged injection holes are barely visible except to an experienced conservator. This treatment approach had the additional benefit of saving the original material of the tenon pegs which would otherwise have had to be drilled out.

Fig. 7 Chair after conservation

Graduate Diploma Conservation Studies

The Graduate Diploma provides the theoretical and practical knowledge and experience necessary to start your career as a conservator and to begin to develop an area of specialisation.

Find out more about the Graduate Diploma Conservation Studies at West Dean College of Arts and Conservation here.

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