by Michka

Building a hemp house sounds like a hempsters dream come true. Yet the fact is, houses are being restored or actually built from hemp in France. This was even the case ten years ago, before the hemp renaissance had begun to take place.

Houses have always been built out of what was available. Where stones and trees for building were scarce, chopped straw was mixed with clay to form walls over a wooden structure. Modern building with hemp differs from these old techniques, yet it too allows for building with what grows around you (at least in a country like France, where hemp has remained a legal crop).

Hemp, when grown for fiber, is sown very densely, so as to have branchless slender stalks. After harvest, the long fibers that make up to about 25% of the stalks are removed. In some parts of the world, like China or Hungary, these fibers are still spun and woven into cloth. In France, the machinery presently used to separate the fibers from the stalk does not allow processing of the fibers into a thread strong enough to be woven into cloth.

Hemp is still grown for its fibers in France, but today these are entirely used by paper making companies (mostly de Mauduy, French company now owned by Kimberley Clarke). Hemp fibers and flax are added to ordinary wood pulp, to make pliable and resistant specialty papers for banknotes or cigarette paper so that, strangely enough, smoking tobacco often entails smoking the fibers of the cannabis plant!

For Cats and Horses

The strong fibers are what hemp has always been grown for: they account, even at present, for about 70% of its commercial value. Yet after the fibers have been removed from the stalk, there remains about 75% of the plant. This bulky by-product, known as hurd (chenevotte in French) looks like fine wood chips, only much lighter.

Hemp hurds are extremely absorbent (about 12 times as much as straw). They will soak up to five times their own weight in moisture. They are commercialized in France by the hemp growers co-op "La Chanvriere de l’Abue" (near Troyes), as bedding for livestock under the brand name Aubiose. Aubiose is used in particular for race horses, who will have nothing but the best. The most minute hurd particles are molded into pellets and commercialized as cat litter. La Chanvriere de l’Aube commercializes them as Biochat in France, or All Hugro in Germany. Since hemp growing became legal in England in 1993, cats there can enjoy the same product, made out of British hemp, as Posh Paws.

Hemp hurds are not only very absorbent, they are also uncommonly rich in silica, a chemical compound naturally occuring as sand or flint. The high mineral content of hemp hurds brings us naturally to  one of their most interesting application: building...and for people too Hemp hurds, when dry, make excellent natural insulation. In damp conditions they tend to absorb moisture. This is why in 1986 La Chanvriere de l’Aube patented a technique that coats the hurds with silica. The resulting product has been commercialized under the brand name "Canobiote". But any loose insulation can turn out to be a cosy home for mice. In my opinion hemp hurds, whether or not they are coated with silica, are at their best when used in a mixture that hardens.

La Chanvriere de l’Aube likes to mix Canobiote with cement, which gives a sort of insulated concrete. Yet it seems a pity to use a natural product like hemp to drown it in cement. Both cement and lime are obtained by heating limestone-but cement also contains clinker (stony matter fused together Webster’s) and a variety of other more or less suspect residues. Besides, it is brought up to such high temperatures that it becomes dead.

France Perier originally worked for La Chanvriere de l’Aube promoting Canobiote, then left to start her own business in a growing area near Le Mans and created a product named Isochanvre. Isochanvre looks very much like Canobiote and costs almost twice as much, yet it is hard to tell what makes the difference between the two products.

One thing is certain: France Perier is concerned with environmental issues. (I remember fondly the excellent organic wine she had arranged to have served at one seminar I attended). The mere idea of mixing hemp hurds with cement is appalling to her. For a number of people, including me, only natural lime is noble enough for this task.

Making Mineral Out Of Vegetable Matter

The basic process is simple: hemp hurds are mixed with natural lime and water. Sometimes plaster of Paris (pure gypsum) or sand is added. The important thing is that hemp hurds, when mixed with lime, undergo a process known as "carbonatation in which the hurds are actually mineralised or petrified (changed to stone). The mixing can be made in a cement mixer. At this stage the resulting mix does look a bit like cement. It can be poured like cement, and likewise it hardens and becomes mold and insect resistant, as well as fire retardant. And yet it retains some of the virtues proper to plant matter: the resulting material, which becomes a lighter, tawnish color when dry, has a texture vaguely reminiscent of cork. It is many times lighter than cement (which workers fully appreciate) and it offers both thermal and sonic insulation (a rare combination). The mixture sets in a matter of hours, while the actual process of petrification continues.

The mix can be poured as a floor or for walls, between sheets of plywood that will be removed a few hours later. In either case, a basic wood frame is needed to support the roof. Here one material replaces several layers of conventional building materials: bricks or cement, vapor barrier, insulation, and plaster board. All that is needed, inside as well as outside, is a whitewash finish, with or without pigments added. Alternatively, for interior use, the look of the material can be preserved with a simple waxing or varnishing, which brings out the cork like structure of the material.

This is the technique recommended by Isochanvre, it can equally be used with Canobiote. And it can also be used in yet another manner, which I find most appealing.

For some people, like Yves Khun, the basic process of petrification is at its best when ordinary hemp hurds are used, not manufactured products like Isochanvre or Canobiote, provided the right kind of lime and plaster of Paris is used, in the right quantities, and in the right manner. This technique, which he has perfected (by slightly modifying the cement mixer for instance) he calls Canosmose.

Khun, a former solo dancer with the prestigious Bejart company, is now an entrepreneur working with his architect wife. They maintain, quite logically, that coating the hurds with silica, in the manufactured products, is unnecessary, and that they are best left untreated,so as to bind more intimately with the lime. They use the hurds such as nature made them. Of course regular hemp hurds, as used for animal bedding, are much cheaper than either Isochanvre or Canobiote (only 270 FF a cubic meter). And very importantly, they are produced everywhere in the world where hemp is being grown. Canosmose is not a brand, but the name of a technique that Yves Khun is happy to share with people anywhere who want to learn about it.

France is one of the few western countries where there has been an uninterrupted tradition of hemp growing. People have been experimenting for a number of years with ways to build with hemp. So it should not come as a surprise that there are already different methods to choose from.

Whatever form of hurds is used, hemp certainly provides a most attractive building material, and is very pleasant to live in. It can compete financially with more common building techniques while being both healthy for people to live in and environmentally friendly.

Useful addresses in France:

La Chanvriere de l’Aube (Canobiote) Chenevotte Habitat (Isochanvre)

Le Verger Rue du General

de Gaulle

10200 Bar-sur-Aube 72260 Rene

Tel: 33-43-97-45-18 Tel: 33-25-27-12-74

Fax; 33-43-97-65-44 Fax: 33-25-27-35-48

Yves Khun (Canosmose)

Ferme La Thuiliere

26560 Monfroc

Tel: 33-92-62-00-74