Restoring colombage walls

Colombage walls - often known as 'half-timbered' walls in other countries - consist of wooden uprights / supports, usually about ten centimetres thick, with gaps between these struts about 20 centimetres wide.

Historically, these gaps were then filled with some kind of thin wooden structure or thin wooden struts, that join the larger posts together, and on to which torchis ('cob' in the UK) is placed. This torchis consists of wet clay, with the addition of chopped straw, cow manure or sand according to local practice and local availability.

This torchis, on the outside of the property at least, is then (traditionally) covered with a render, made from lime and sand. Sometimes the wood is also covered over with this render, sometimes it remains visible. You will be familiar with the appearance of a wall like this from old houses in both France and the UK and almost always with an appearance of age and beauty.

With old houses in France the torchis has often started to fall out of the gaps between the wood, and the exposed and unprotected wood has started to suffer from the ravages of the weather and wildlife. So it is necessary to restore the wall.

Before you start you need to be sure that the wood structure itself is sound. This may involve your local carpentry company, but wood that is too weak will need to be replaced. Don't be too keen to remove the old wood though - if the wood that is currently supporting the wall looks to be in a very poor state, it is quite likely that it can continue to support the wall, on condition that further deterioration can be prevented. It is difficult to add new struts without altering the appearance of the wall, and the ravages of time all add to the beauty and appearance of the existing wood.

On one occasion we were able to add a new beam across the top of the colombage wall, so the new beam was actually supporting the roof and supported at each end on existing stone walls, thus making the colombage wall "non-supporting", which is quite a satisfactory solution. Similarly on another building we renovated, the roof has been supported in an alternative fashion, thus rendering the colombage "decorative".

An alternative possibility is to decide that the colombage will be visible on one side of the wall only - that is, either inside the building or outside the building (either is possible). It will be then be easy to construct a supporting wall or add reinforcing struts on the side that is to be "invisible". This will also help with insulating the walls, since the insulation can be added in the gap between the new wall and the colombage wall. Incidentally, torchis itself is a very good insulant, although a wall 10 centimetres thick is never going to be the best insulated.

At this stage, you should also thoroughly treat the wood against woodworms, termites, capricorn beetles and so on. Colombage walls are usually held a few inches away from the ground - traditionally on a low stone wall, this is designed to separate the wooden structure from the damp ground. You need to ensure that the wood is not subject to damp rising from the ground.

The torchis itself will usually need repair or replacement. There are several possible approaches, depending in part on the existing condition. If the torchis is in a very poor condition, it will be necessary to remove it and replace it. If it is still reasonably intact and quite secure it may be possible to simply brush it with a wire brush to obtain a firm support. Several modern replacements for torchis are available:

• real 'earth' based products (for example, from a company called Akterre in France), which take the form of earth and straw, to which water is added, and formed into brick shapes which can be cut to size and then built up in the gaps
• insulant based products, including hemp (available from a company called Isochanvre in France) which can also be cut to shape and size easily
• brick type products, with thin bricks being used to fill the gaps - each brick will need a nail to be hammered into the adjacent wood and then hooked under the brick, to provide extra support and rigidity. This approach is perhaps best used for small wall areas only
• It is possible in some areas to find a local artisan who can recreate the wall using the original construction techniques.

The next stage is to crepi (render) over the top of the torchis, using a mix of lime and sand. Your friendly local builders merchant will have reinforcement fibres which should be added for extra strength.

It is not very easy for the non-professional to get a very good finish on crepi, although since the wll is old and 'rugged' you mght not be concerned about achieving a perfect finish anyway.

The professionals wait for the crepi to be quite hard but not completely set, and then they rub it enthusiastically with a tool that consists of a handle attached to a flat metal plate about 15 centimetres by 20 centimetres, which has stiff metal bristles sticking out (NOT a wire brush, which has much more, less stiff, bristles).

Now all the hard work is finished, and when the crepi is dry you will probably need to give the wood a good clean to remove any residual surface render.

The exposed wood should now be protected. This can be done with an off the shelf stain or varnish, or for more authenticity you can use a mix of 3 parts linseed oil (huile de lin), 1 part turpentine (terebenthine) and a small amount of drying agent (siccatif) which helps the oil 'set'. Although cheap, quick and traditional, this will need to be redone every year, whereas varnishes and other bought products will usually last many years between applications.