History and uses of hemp - The Hempcrete Topic: Designing and Building with Hemp-lime - page 5

The hemp plant, thanks to its many uses and in particular its most famous one, as a
widely popular recreational drug, is one of the most instantly recognizable plants in
the world. A great deal has been written about hemp's many uses throughout hu-
man history and about the politics of its prohibition during the twentieth century,
and there is no need for us to reproduce it all here. In the interests of context,
however, in this chapter we provide a brief description of the hemp plant, its history
and the resurgence in its use today.
Hemp is the English name (from the old English haenep ) for the cannabis plant. The words
haenep and cannabis are both thought to derive from the Ancient Greek kánnabis , which
in turn evolved from an older word in an ancient Iranian language from around 2,500 years
ago.
Three varieties of the cannabis plant exist: Cannabis sativa, Cannabis indica and Cannabis
ruderalis. Cannabis sativa and C. indica are seen as the more closely related species. Can-
nabis ruderalis differs from them in that its flowering happens after a predetermined num-
ber of days, rather than being dependent on the seasons, and it contains very little tetrahy-
drocannabinol (THC), the psychoactive substance that gives the drug cannabis its active
ingredient.
Hemp is a fast-growing erect annual plant which produces only a few branches, usually
at the top of the plant, and grows to a height of between 1.5m and 4m. Its stem is thin
and hollow, with a diameter of 4mm to 20mm, depending on the conditions and the spe-
cific variety grown. The 'bast' fibres of the hemp plant, which are contained in the bark of
the woody stem, range from about 1.2m to 2.1m in length and are extremely strong. Their
quality varies depending on the timing of harvesting, and the fibres are graded in terms of
their fineness, length, colour, uniformity and strength.
The inner woody stem, the 'shiv' (or 'shive', or 'hurds'), historically has not been used in-
tensively, but this is changing rapidly in the modern world, with new uses being developed
all the time: packaging filler and animal bedding, for example. It is hemp shiv that is used
in the production of hempcrete.
The seeds of the hemp plant are used as a food source, and ground to produce oils for a
wide range of purposes, including technical and industrial applications. The hemp plant in
its whole state can be used as a biofuel, and even the cell fluid of the hemp plant is now
used in the manufacture of abrasive fluids. 1