Restoring and renovating colombage in France

Restoring a Colombage Wall

Colombage consists of wooden struts / supports typically ten centimetres thick, with gaps between them of perhaps 20 centimetres. These gaps are historically filled with some kind of thin wooden structure or thin wooden struts, joining the larger posts together, and on to which ‘torchis’ (‘cob’ in UK) is placed. This torchis essentially consists of clay, with the addition of chopped straw, cow manure or sand according to local practice.

This torchis, on the outside of the house at least, is then covered with a render of 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 – almost always with an appearance of age and beauty.

The problem often arises with houses bought in France that the torchis has started to fall out of the gaps, and that the wood has suffered from the ravages of weather and wildlife. So an approach is needed to restore the wall.

 

Firstly, the wood structure has to be sound. This may involve your local carpenter but wood that is too weak will need to be replaced. Don’t be too harsh 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, if further deterioration is stopped. It is difficult to add new struts without altering the appearance of the wall, and the ravages of time all add to the appearance of the wood. On one occasion we were able to add a new beam across the top of the colombage wall that was supporting the roof, 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, the roof has been supported in an alternative fashion thus rendering the colombage ‘decorative’. An alternative approach might be to decide that the colombage will be visible on one side only - that is, either in the building or outside the building. Then it will be easy to construct a supporting wall or 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.

 

section of colombage wall (internal, not rendered)

This is a good stage to treat the wood against woodworms, termites, Capricorn beetles and so on.

 

The torchis itself will often need repairing or replacing, and there are several possible approaches, depending in part on the condition. If the torchis is in very poor state, it may 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. Common modern replacements for torchis include:

• earth based products (for example from a company called Akterre in France), which can take the form of earth and straw to which water is added or earth formed into brick shapes which can be cut to size and then built up int 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 also possible in some areas to find a local artisan who can recreate the wall using original techniques.

Having obtained a solid base in the wall, it will the be necessary to crepi (render) over the torchis, using a mix of lime and sand (pay heed to local sand colours) and reinforcement fibres. It is not very easy for the non-professional (myself included) to get a very good finish on crepi – the professionals wait for the crepi to be quite hard but not completely set, and then rub vigorously 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).

 

You will then probably need to give the wood a good clean to remove residual surface render – a pressure washer would help, but try not to pressure wash the new render too enthusiastically.

 

The wood can then be protected either with an ‘off the shelf’ stain or varnish, or more authentically with 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 go hard. Cheap and quick, this will need redoing every year, whereas varnishes and other bought products will of course last many years.