A play on the name concrete, hempcrete is a mixture of hemp and lime to form a building material. It also goes under many other names, the most notable of those is hemplime. Hempcrete uses the stalks of the hemp plant. Not the sort that people use to get high, but a fibrous variety grown specifically for its fiber uses such as making hemp rope, or hempcrete.
The mixture of hemp fibers and lime can be used as a high quality insulation infill. It does not have the structural rigidity needed to support load bearing walls. It is also significantly lighter than concrete and very easy to work with as a moldable material. It is often used between normal timber frame construction as an insulation. Outer forms have to be placed until the hempcrete has had a chance to properly dry.
Once dry, it is resistant to seismic disturbance and is an excellent choice for those living in areas with a high likelihood of seismic activity. France, where hempcrete was first created is its current biggest proponent. It is stated that it may have even been created as long ago as the 14th century where it is reported to have been found in use in a bridge in France. Though it is only recently, the 1990s that the material has seen a resurgence of interest.
Though it is too lightweight for load bearing, it is find a lot of use as insulation. Helping to regulate moisture in buildings as well as giving a high degree of thermal insulation. The high silica content of hemp is what allows it to bind so well with the lime to create this excellent and renewable material.
As interest in this material increases, research will undoubtedly follow and perhaps soon we will see the material being taken more mainstream. Until then, this is an excellent green building material to keep an eye on and think of ways to creatively be put to use. Especially considering the durability of this building material since the other examples of its use are several hundred of years old.