The hempcrete wall: an overview - The Hempcrete Topic: Designing and Building with Hemp-lime - page 212

When the hempcrete has dried sufficiently, it can be finished internally with lime or clay
plasters, with these being applied directly to the surface of the cast hempcrete or to the
breathable permanent shuttering board. Or, if the texture of the face of the hempcrete wall
is to the occupant's taste, it can be left as cast, with just a natural, breathable paint applied
directly on to the hempcrete. All paints used on hempcrete, whether applied directly to the
wall or on top of finishes, must be breathable.
Externally, a hempcrete wall is usually finished with lime render, but might alternatively
be clad with a natural material (e.g. timber, slates, tiles, brick or stone), as long as a vent-
ilated air gap is left between the cladding and the face of the wall, and breathable lime
mortar is used for any masonry. For a rendered wall, again, breathable paints or limewash
are used externally. The principle of the 'breathable' wall made with natural materials is
discussed in Chapter 4 .
Structural maintenance
It is worth reminding ourselves here that, while all natural materials used in a wall allow
the absorption and desorption of moisture by the wall over time without damage to its fab-
ric, this does not mean that hempcrete walls are maintenance-free! As with any building,
periodic maintenance is required over the years, to keep it working as it should. Sadly, you
can walk down any street and see examples of conventional structures where the failure of
the occupants to carry out simple maintenance tasks, such as cleaning out or repairing gut-
ters, or replacing slipped roof tiles, is causing problems with damp and structural deterior-
ation. Finally, a key principle to bear in mind when using any plant-based natural building
material (e.g. hemp, straw, timber, reed) is that any exposure of such materials to stand-
ing water, or to water constantly running through them, will eventually lead to the material
rotting. Of course this is nothing unusual, since most materials, not just natural ones, will
deteriorate if exposed to standing water! This is another good reason to keep up with main-
tenance (especially of the roof), and it has implications for the design of the building, as
discussed on page 133 .
Hempcrete wall construction method
This section describes the process of constructing a typical new-build hempcrete wall. Oth-
er chapters in this part of the topic address in more detail each aspect of the construction.
For a full discussion of hemp and lime materials, see Chapters 2 and 3 .