Floors, ceilings and roof insulation - The Hempcrete Topic: Designing and Building with Hemp-lime - page 382

Placing hempcrete in a ceiling.
The method for casting a ceiling out of hempcrete takes its inspiration from the mechanical
structure of lath and plaster, with small-section timber battens acting as the 'laths', provid-
ing a key, and the hempcrete being in place of the basecoat plaster. This is illustrated in
Figure 33, page 330 . The basic method is as follows:
Timber battens of 20mm x 35mm section or similar are fixed to the underside of the
rafters or joists, running perpendicular to them at 150mm centres. These act as the key
for the hempcrete and provide the structure and reinforcement of the ceiling.
There are two options for shuttering the underside of the ceiling: you can fix OSB
sheets directly to the battens, which leaves the battens showing in the surface when the
shuttering is removed, or you can hang them underneath the battens by about
20-25mm, so that continuous hempcrete makes up the surface of the ceiling. Fixing
shuttering direct to the battens makes placing the hempcrete easier, as you don't have
to get it underneath the battens, but plastering is harder owing to the varying back-
ground. Conversely, if you hang the shuttering underneath the battens, it is harder to
hempcrete but easier to plaster.
Whether your battens are showing or not, it is recommended to use a fibre reinforce-
ment mesh in your basecoat plaster, or a haired lime basecoat.