Placing hempcrete - The Hempcrete Topic: Designing and Building with Hemp-lime - page 355

The basic method for placing hempcrete is as follows:
Tip the contents of a tub of hempcrete into the shuttered void so that it forms a layer of
loose hempcrete around 100-150mm deep but no more. Any deeper than this and it will
be difficult to compact evenly and consistently, leading to loose or dense areas in the
finished material.
With a gloved hand, spread the mix out evenly to make sure it fills the whole void to
the same level.
Pay particular attention to any hard-to-reach areas, such as small corners around doors
and windows and around horizontal frame timbers (see page 213 ) .
Consolidate areas around the frame timbers and against the shuttering using the tips of
your gloved fingers, always bearing in mind the desired finish on the surface of the
wall (see page 209 ). If using permanent shuttering, there is no need to consolidate the
hempcrete next to these boards.
Spread it evenly once more to ensure that the compaction is consistent, and check that
the above areas are still well consolidated. n For hard-to-reach areas you can use a
stick, e.g. a length of roofing batten, as an extension of your hand, using the same
method as with your hand. Apart from this instance, avoid using 'tamping sticks' gen-
erally, as this tends to encourage over-compaction.
At external corners, and at window reveals, a little extra compaction of the hempcrete
as you place it is a good idea, to give these vulnerable areas a little more strength in the
set material, and thus maximum resistance to knocks and bumps.
For certain applications - usually in solid-wall insulation or historic work - where a
thinner section of cast material is being placed (e.g. 150-200mm), it may need to be
tamped more firmly than usual to increase the strength of the material, but this should
still be kept to a minimum. If you are casting that thin then you don't really have much
leeway for a reduction in thermal performance. If in doubt, experiment by casting a test
panel at a low density, letting it dry for a week or two, and testing the strength of it.
When placing hempcrete over any opening in the wall, the section immediately above
the opening up to at least 300mm above it, and extending at least 300mm either side,
needs casting in one go, so that a single cast-in-situ 'lintel' of hempcrete is formed.
Where the opening is not formed by permanent shuttering then some sort of reinforce-
ment needs casting into the hempcrete to support it while it dries, e.g. battens spanning
the opening (see Figure 37, page 339 ).
When you reach the top of a shuttering section where no hempcrete will be placed dir-
ectly on top of it, e.g. a windowsill, over-fill this section so that the hempcrete sticks
out of the top of the shuttering. This is necessary because the exposed section at the top