Restoration and retrofit - The Hempcrete Topic: Designing and Building with Hemp-lime - page 457

properties. However, not all conservation officers have had first-hand experience of hemp-
crete, and some may need convincing before they are prepared to sanction its use. The
main issue we come up against is a concern that the hempcrete will be applied in such a
way as to alter the building's fabric in a way that cannot be reversed at a later date if neces-
sary. However, this should not be the case, as long as application techniques appropriate
to the situation are used, and such objections can usually be overcome with the provision
of detailed information to the conservation officer and clear explanations of the proposed
work. For example, spray application is not suitable for all aspects of work in historic
buildings, owing to the force with which it is projected. When casting solid-wall insula-
tion up against a hard stone wall, the force of projection causes no problems and in fact
is an advantage, as it helps the hempcrete adhere to the surface. However, when casting
up against the back of surviving plasterwork or wattle and daub, spray-applied hempcrete
would adhere too closely to the historically important material, making later reversal of the
works impossible without damaging the original fabric. For this reason, in most situations
in historic properties, hand-placing is a more appropriate method.
It is recommended that anyone applying hempcrete in heritage buildings should not only
be competent in the use of the material but also have specialist skills in, or at least un-
derstanding of, the repair of heritage buildings. This should include the repair of timber
frames, cob, stonework and heritage roofs, and the use of lime (including fat lime - lime
putty - plasters) and, where appropriate, clay mortars and plasters. It is not necessary for
the hempcrete contractor to be skilled in every one of these areas, as other specialist con-
tractors can provide these services, but an understanding of all of them is needed in order
to be able to take a holistic view of the building and thereby design hempcrete insulation
solutions that will complement and enhance the way the existing building fabric works.