One of the most attractive features of many of the old houses in France is their exposed beams. If they are dry, they can last for hundreds of years with no particular care and attention.
To ensure the continue to be both beautiful and strong, renovation projects usually include a review of the condition of the exposed beams, then some sanding or sandblasting, and removal of decayed wood. This is then followed by wood treatment, to protect against wood-boring insects.
Even if old beams look to be in a bad condition they are usually still very solid on the inside.
It has often been said to me that woodworm and other wood-boring creatures can not eat into the hard centre of the wood, so no real harm will be done. Although this is usually the case it is not a fixed rule. As an example, some old beams are made from a softer wood – poplar, for example, instead of oak. This softer wood is more vulnerable to being eaten right through. Even with old oak beams, I have had cause to cut through a few and on at least one occasion there was certainly some damage right to the centre of the wood. It is very unusual though – possibly because the wood has been damp at some point.
The usual way that the condition of wood is verified is by banging three inch nails into it with a hammer. If the nail won’t go in, or only with great difficulty, the wood is in good condition. If the nail goes in easily there is a strong likelihood that the beam will need replacing. More pessimistic people do the same test with a screwdriver or a stanley knife – same result, but it will tend to identify beams with significant surface damage as needing replacement.
The main place that exposed beams are susceptible to problems in normal use is the point where they are set into the wall, at the ends of the beams. The humidity of the wall can cause some permanent dampness in the wood, which can lead to weakness, rot and invasion by boring insects, so this is the part that should be tested most thoroughly.
If your beams do need replacing you are very likely to need professional advice and help, since the beams are probably acting as a support for the floor or structure above. In any event, since there are load-bearing and other structural considerations it is outside the remit of this site.
After you have checked that the beams are in a reasonable condition, the next stage is to remove all the weak, decayed and crumbling wood from the surface of the beam, until you can find some solid wood. The tools to use will depend on the amount to be removed. i have used everything from sandpaper to hammer and chisel at various times. The amount of general sanding required will be greater if the wood has been painted or gloss varnished at some earlier stage. In this situation sandblasting (with care) may be the best approach.
After you have done, sand the wood to remove residual damaged wood and provide a clean, solid surface.
A quick wash with detergent water should then suffice to finish the preparation.
There are several treatments available for protection against wood-boring insects. In France the most commonly used is Xylophene.
NOTE ADDED LATER: Xylophene is VERY toxic. You MUST follow the safety instructions, including the wearing of protective gear and an appropriate breathing mask. As an alternative to xylophene it has been suggested to me that boron can be used (I have no experience of this, please research on the internet if you are interested).
The treatment liquid should be brushed vigorously onto the wood, while a long-nozzled plant sprayer can be used for inaccessible corners and gaps if necessary. Two coats is recommended for sound wood or three coats for infected wood.
You should not be living in the property at the time of treatment, since the fumes tend to get everywhere and are quite noxious. In any event, during application, the wearing of suitable protective gear is imperative.
Specialists will sometimes recommend more intensive wood treatment. Typically this will include drilling some holes in the beams every few centimetres, and then injecting treatment at high pressure into the heart of the wood. This is probably beyond the scope of DIY. In any event a professional company will also offer some form of guarantee.
I am not personally convinced that the benefits of doing this are significant, because the damage to the wood is largely along the surface of the wood, and the holes drilled could weaken the wood more than any insect. I am not one to get over-neurotic with treating wood that has been standing without any treatment at all for 200 years. You are welcome to disagree with me on this. The sound of capricorn beetles munching your roof beams can be a very persuasive argument.
The wood treatment should be redone every few years to ensure continued protection. Of course, the ongoing risk to the wood is much less in an inhabited, restored, clean, dry and broadly insect free building than in an old derelict building.
None of the above comments applies if you have evidence of termites at the property. I would not adopt my casual approach if I found these in my house. Termites always need professional treatment. Although Xylophene and other products say they can deal with termites, you will always need an expert if you find evidence of a termite infestation. Any confirmed sighting of termites at your property must also be reported to your local mairie.