Getting the basics right - The Hempcrete Topic: Designing and Building with Hemp-lime - page 93

The main reason for constructing walls out of hempcrete is to equip the building
with a very high standard of insulation without resorting to the use of synthetic insu-
lation materials, which have a high embodied energy and are produced from non-re-
newable materials - usually petrochemical derivatives or synthetic fibres.
Hempcrete is a relatively new construction material, about which the general public is only
just becoming aware. Perhaps because of this, we at Hemp-LimeConstruct frequently get
enquiries, even from people seriously considering using the material in their building, from
which it is clear that the basic principles of building with hempcrete are not fully under-
stood. In the case of clients who are employing someone else to do the construction work,
clearly there is a limit to the level of detail they actually need to know about the process.
There are, however, certain concepts that they will need to understand in order to maintain
their hempcrete building in good order.
For those considering building with hempcrete themselves, however, it is obviously im-
portant that they know what they are doing, and that the basic principles are understood at
the start, so that mistakes are avoided later on. This chapter, therefore, provides an over-
view of the key principles of hempcrete building. Some of these themes have been intro-
duced in previous chapters, and we return to them all throughout the topic, but gathering
them together here should serve to highlight their importance. At the end of the chapter is
a brief overview of problems that can occur with hempcrete as a result of lack of under-
standing of the material and the construction process.
The nature of the material
Hempcrete is essentially a modern version of very old natural composite construction ma-
terials, such as wattle and daub or cob. While it is relatively low-tech in its composition
and application, the quality of workmanship throughout the construction phase can make a
huge difference to the finished material.
The material is formed by wet-mixing hemp shiv (the chopped woody stem of the indus-
trial hemp plant) with a lime-based binder. The cast-in-situ method involves casting it in
'moulds' made from temporary shuttering, which is taken down as the hempcrete begins
to dry. Hempcrete is also available as pre-cast blocks or panels, but cast-in-situ hempcrete
is the focus of this topic.