October 5, 1997

Hemp for Houses

     Just about everybody knows by now that hemp can be used to make thousands of valuable products, everything from food, clothing, and shelter, to fuel, rope, paper, soap, cosmetics, and just about everything else you might need or want. Anything you can make with petro-chemicals you can make with hemp seed oil, for instance.

     Well, but so what? Is there anything better about using hemp than other materials? Yes, there is. There are generally two categories of advantages for using hemp: ecological and economic. Since hemp is a natural material that can be grown without pesticides or extensive use of fertilizers, and processed without toxic chemicals, it is ecologically way above such alternatives as cotton for clothing or wood pulp for paper. But it is the economic benefits that are causing accountants to sit up and take notice. Hemp clothing may cost twice as much as cotton, but since it lasts six times as long, it really ends up being much cheaper in the long run. And hemp can produce at least four times as much pulp per acre, on a sustained yield basis, as wood pulp.

     I am a papermaker, forming handmade sheets at the vat with a mould and deckle, and I have been using hemp (as well as kenaf, abaca, and roadside weeds) in my papers for about six or seven years. Most of my interest in hemp has been paper related, and I am now in the formative stages of bringing a new technology to market that will allow a large scale production of pulp for paper to be made from whole stalks of hemp along with agricultural waste material (see information on our web site: www.tree.org). This process will make pulp in a very ecologically friendly way. It is a closed system with no toxic effluents and no use of chlorine or other offensive materials. Furthermore, the process ought to cost substantially less than wood pulp alternatives, at least once we have a few years of development and refinement under our belt, and we are able to build mills on a scale to compete with the established wood pulp industry.

     But now, through contacts associated with that endeavor, I have found myself with extensive documentation of research efforts, mostly originating in France, of using hemp as a building material. I have been experimenting with these materials and procedures with very satisfying results, and I predict a huge growth industry in this process.

     But first, let me narrow the field of my own research. Quite a lot of interest and investigation has gone into the effort to re-invent the wooden board. Basically, some version of heat and pressure, along with some binding agent, is used to create a medium density fiber board with properties superior to wood at potentially lower cost. Some efforts are geared to produce much harder and denser plastic materials, but the basic idea is the same. The problem is in the binders. There are plenty of binders that will work just fine, but they are not ecologically friendly, and so there is not a lot of interest in their use. On the other hand, there are plenty of ecologically friendly binders, but they are either too costly to be viable, or they don’t work very well.

     One of my European contacts assures me that he has found the Holy Grail of the potential hemp building materials industry: the cheap, effective, and ecologically friendly binder that will launch the industry into the big time. At this point it is premature to mention anything further about this, except to say that I will be getting more information about this shortly and will be making efforts to bring it to market. Perhaps it is not inappropriate for me to suggest that anyone working on pressed hemp boards might want to get in touch with me to collaborate over binding agents.

     But there is another quite different approach to using hemp as a building material, and it is an approach that makes more sense to me all the way around.

     I have made some little research into ecologically appropriate housing materials and methods, and I have made a list of the criteria for the healthy house: it should be made as much as possible from an efficient use of locally available materials; it must have good working value (it must be strong, durable, water-proof, fireproof, have good insulating value, etc.), and it must be cheap to build from the standpoint of both materials and labor cost. Furthermore, it must use only ecologically friendly materials and construction methods that respect our environment. It must use less energy to build and operate (heat and cool) and fewer non-renewable resources than conventional housing.

     One rule of thumb is that when a process (like building a house) remains as close to the earth as possible, with a minimal disturbance of the earth’s resources, then it will end up being very cheap to build. This suggests that the cheaper your house costs to build, the more ecologically correct it is. Of course that is only a general observation, but what it means is that cost is the real benefit of efficiency in the use of resources.

     By all of these measures, the hemp house wins the prize. What you do is frame in your structure using spacing as wide as local codes will allow – at least 24", but there is no reason why you couldn’t get by just fine with 48" spacing. In northern latitudes, you will use wider framing boards, 2x10s, for example, for greater insulating efficiency. In moderate climates, 2x6 construction ought to be adequate. Next, you case in these spaces by tacking plywood to the frame. Then you fill in the spaces with a mix composed of hemp hurds (the woody core, after the more valuable bast fiber has been removed) combined with lime, sand, plaster, cement, and just enough water to dampen and mix the materials. The material is tamped well and then left to set up overnight. In the morning you remove the casings and find that the material has set up into a kind of concrete.

 . . .

     That’s it; you’re ready to move in. You do not need to add any additional exterior or interior wall coverings, nor do you need insulation. For a more finished appearance, you can apply a top layer of lime and sand to the exterior wall, and plaster (with pigments added if desired) to the interior wall. The entire frame can be built over a foundation slab composed of the same material, with slightly different proportions.

     That is the basic idea, but there are many design options. The "boards" specified may be anything you want to use. This can be the time when the added process technology (hence cost) of using pressed hemp particleboard may be warranted. Or, you may want to recycle some existing wood. I have a bunch of very rough redwood posts that I want to recycle that must have originally been 6x6. I could frame it in the style of an Elizabethan mansion and leave the posts exposed, or I could cover the whole structure with a top coat to give it a more uniform finish and better insulating value.

     When this construction method is considered, it appears to meet every one of the goals for the ecologically appropriate house. The materials are very inexpensive and can be prepared on-site with nothing higher tech than a cement mixer, yet it sets up into a solid mass that literally turns to stone and just gets harder and stronger as the years go by. It has a very high comfort rating: the walls are waterproof, weather resistant, and have high insulating properties, yet the walls "breathe" so that you do not have the suffocating feeling of being sealed in a plastic bag, like a modern office building.

     Best of all, the material is cheap and abundant. – or it should be! After all, so many tons of industrial hemp are being processed and decorticated every day so that all that bast fiber can be sold for textiles and fine paper, right? Actually, at this point there is a divergence between the theoretical and the actual. This construction technique was pioneered in France (well, ancient Egypt, but France more recently) in the midst of their flourishing industrial hemp industry, and there really was a great abundance of hemp hurds (about 70% of the stalk) quite cheaply available, already bagged and ready to be taken away.

     However, in order to experiment with this building technique, it really didn’t make much sense to me to import a boat load of hemp hurds from China or South America in order to build a "hemp house" here in California. The only reason why the idea is not totally as silly as it sounds is that it could demonstrate the feasibility of the process and material, and lead to the days when we will be able to pick up bags of cheap hemp hurds from any number of local farms. But for right now, the hemp hurds are neither locally available nor cheap. But I compared the situation to what I am already familiar with, papermaking, and I had (and have) the same idea: instead of making paper (or houses) with 100% hemp, why not use the hemp for its valuable properties, but supplement it with agricultural waste, such as that 1,500,000 tons of rice straw that is annually burned off the fields in the Sacramento valley of California? (Actually, I think they have stopped the burning of the straw, but it is surely available for little more than the cost of taking away.)

     So I have done this. I have been making experiments of the basic process, yet I have used chipped roadside weeds, such as teasel (Dipsacus sativus), with or without added hemp hurds, instead of just using hemp hurds alone. I have been looking for weeds that have good fiber and cellulose, and also high silica content (one of the components of the chemical process that turns the hemp into stone). My theory is that using the whole stalk of teasel, including such bast fiber as it may have, can be as good as using hemp hurds, with all of the bast fiber removed. My experiments seem to be working just fine no matter what I use. My thinking now is to use a mix of available fibrous stalk from farm waste combined with rice and oat straw, and later on using hemp when it is more plentifully available. The argument for using the hemp is clear: if it were abundantly available locally as the byproduct of an industrial hemp plantation, then it would be the cheapest and best source of raw material, since its chemical composition is ideal and it doesn’t need to be harvested or chipped.

     But for right now, I am using weeds, and all of a sudden my building projects are beginning to look pretty affordable. I recycle various framing materials, build my walls with weeds, and all I have to pay for is the cement mixer and the bags of binders. It is so easy I can do it myself (with a little help). I have enough projects on my own land to keep me busy, but I am also interested in forming a commercial construction company to advance this process on a larger scale.

     I believe that this building process can have wide application all over the world, wherever high quality affordable housing is needed or wanted.

     --and its implications for the cultivation of hemp are considerable. If there is any industry that could rival the potential tonnage of hemp for paper, it is hemp for houses.

John Stahl
Agstone Construction

email: tree@tree.org

Go to: Earth Pulp and Paper

Go to: Hemp Building Materials