Hemp in construction - The Hempcrete Topic: Designing and Building with Hemp-lime - page 30

For self-builders wanting to carry out the work themselves, sprayed hempcrete is not really
an option. The expensive machinery is not something you can hire by the week, and in any
case the skill required to operate it can only be developed over time. However, spray-ap-
plying has the potential to reduce the number of people needed on-site during the place-
ment of hempcrete, especially on large-scale builds. Against this, of course, you have to
factor in the capital outlay, and time and money spent cleaning, transporting, maintaining
and repairing the machine.
For builds of up to around 100m 3 (a very large house or large community building, for ex-
ample) the costs of hand-placing and spray-applying are comparable, with any variation
usually depending on the frame design and site-specific issues. As you start to move up to
larger builds, spray-application really comes into its own.
Pre-cast hempcrete
As an alternative to in-situ casting, hempcrete can be pre-cast into either blocks or framed
panels. This usually brings distinct advantages in terms of predictability of the build pro-
cess, since in most types of pre-cast hempcrete construction the drying of the hempcrete,
or at least most of it, is completed off-site, so any uncertainty regarding the time needed
for this is eliminated. This is a particular advantage for the schedule of works in large-scale
commercial builds, and times when the construction phase must take place during winter.
However, the downside of pre-casting is that it is often a more complicated way of using
hempcrete, with a higher number of processes and materials involved. This in turn means
that it may be a less sustainable construction method, although in truth, accurate compar-
ison between cast-in-situ and pre-cast hempcrete is extremely difficult owing to variables
such as the scale of the build, design details, the materials used and the distance between
farm, processing plant, factory and site. The main pros and cons with pre-cast methods are
outlined below.