Mixing hempcrete - The Hempcrete Topic: Designing and Building with Hemp-lime - page 340

Carefully add all the measured-out water, and then all the binder, to the mixer, with it
switched off to minimize the amount of dust that is released into the air. With the
wheeled type of mixer you can set the mouth of the bell to face up to near-vertical to
make adding the binder easier.
Turn on the mixer, watching out for dust that escapes before the binder and water have
mixed together (although you will have your mask on, warn any other people working
nearby, who may wish to retreat to a safe distance).
Once the water and binder have mixed to a consistent slurry, add the first bucket of
hemp (about a quarter of the total), then the second, in fairly quick succession. Half of
the total hemp is now in the mix, and your wet slurry will now be thickening, but is
still quite liquid.
Next, add the third bucket of hemp, and set the wheel on the mixer to the angle closest
to horizontal at which it will mix without the contents falling out.
Mixing in a bell mixer: step by step
At this point, watch the mix as it turns, because it now becomes important not to leave
the hempcrete mixing any longer than is necessary, otherwise it starts to form into
balls, preventing an even mixing of the hemp and binder (see below).
When the third quarter of hemp is evenly distributed, stop the mixer and reach in with a
gloved hand to pull off any mix that is stuck to the back of the drum. Then start-stop it
once to turn the bell through 180 degrees, and repeat the process.
Start the mixer and add the last bucket of hemp. Watch it closely and don't let the mix-
er turn any more than it needs for all the hemp to blend in and become a consistent col-
our (approximately 1 minute).
Stop the mixer and pull any mix off the back as before, then let it turn for a further 10
seconds.
Stop the mixer. Your mix should now be ready.
To test whether it is the correct consistency, use the ball-and-finger test described on
page 200. You are trying to achieve a light fluffy mix, whilst avoiding the mix balling
up (see also page 200 ) . Balling up is best avoided by keeping the mixing time to the
absolute minimum necessary. In a bell mixer a perfectly good mix will turn to balls if
you leave it going too long. Keeping the mixer in the most horizontal position possible
after you add the second half of the hemp also helps to prevent balling.
If the consistency is not right, adjust it by adding a tiny bit more water or hemp and
binder accordingly, turning the mixer only the absolute minimum for all the hemp to
mix in consistently, as described above. If necessary, adjust the amount of water you
will use for subsequent mixes (never adjust the ratios of binder to hemp).