Placing hempcrete - The Hempcrete Topic: Designing and Building with Hemp-lime - page 356

can dry too quickly and become loose and friable. Over-filling allows the loose hemp-
crete to be cut off after it has dried (using an old saw or multi-tool), back to the solid
stuff at the required level (see photo overleaf, bottom left).
Ensure that the wet hempcrete mix is placed well before it has started to take its initial
set. This is not usually a problem, unless using Prompt Natural Cement, which has
quite a short window of workability - though this can be increased a certain amount
through the judicious use of Vicat's Tempo (citric acid) retardant (see page 46 ). If you
use Prompt after it has started to go off, strong bonds are not formed in the cast materi-
al, leading to loose mix which can disintegrate when the shuttering is removed.
(Thankfully such patches can be remedied if they don't extend too far: see page 214 . )
Although no manufacturer specifically recommends a maximum daily lift in their liter-
ature, it is much better as a general principle to move around the whole building to the
same level before moving up again. This is so that the placed hempcrete has the max-
imum possible amount of time to begin setting before extra weight is placed on top of
it. Unless your walls are very short, meaning that you would complete each lift very
quickly, you are unlikely to have any difficulties in this regard. We have occasionally
done lifts of 2 metres in a day without experiencing any problems.
When a day's work does not take you to the end of a run of shuttering, it is important
not to come to a 'sudden' stop. Vertical day joints are to be avoided, because they have
the potential to weaken the cast material. Instead, slope the end of the placed hemp-
crete down gradually over several metres, so that a gentle slope is formed as the day
joint, and build up from this the next day.