Promote • Educate
56 September/October 2019
Building and technology
Organic & Ecological
Interiors & Homewares04 972 5612 [email protected]
verdantdesign.co.nzNow open at 27a Webb St
Te Aro WellingtonLincoln University has grown and trialled
it. Originally from Asia, this large clumping
grass is a very strong fibre, and rot resistant.
“You can get amazing yields – 20 tonnes
per acre per year,” says Grant. “Also you
can grow it on marginal land – it doesn’t
need fertiliser – as long as you can get farm
machinery onto the land to harvest it.”
Sounds ideal for parts of the East Coast.Heavy, light, or just right?
Light earth was invented in Germany, says
Grant, and there they use less clay because
it’s cold. He terms his own building style
‘heavy light earth’, combining thermal
mass and R-value (insulation). Solid earth- adobe – has thermal mass, but very poor
insulation values. “It’s OK in Mexico or
Arabia, but not in New Zealand.”
Grant is not such a fan of straw bale
building, although agrees it can work well
in drier climates. “Straw bales can rot,
get infested with vermin, and need a big
foundation and roof to accommodate very
thick walls. I still do concrete floors because
earth floors are too slow [to make].”
“Clay is a preservative and a desiccant.
It has very low moisture levels to the point
that fungus and insects can’t thrive.”
Bottle bank
One project Grant is working on is adding
an external layer of light earth onto the
outside of a Skyline garage, for insulation.
You wouldn’t know to look at it, but there’s
a secret ingredient stashed away in there.
About 2000 Steinlager bottles are mortared
together with hay, local clay, a little cement,and a green oxide pigment added to the
mix. A wooden lattice of macrocarpa holds
it in.
More bottles are incorporated into the
shed out the back, and some are visible as
an artistic feature. The light earth mix for
the shed includes chipped up mānuka,
pampas grass and wood shavings. The back
wall has a finishing plaster of cow manure,
casein (quark, milk powder), clay, beach
sand and linseed oil.Working together
In the paddock over from the house is the
community building yard, where students
and locals work together to make light
earth bricks. Clay slurry (technically a slip)
is mixed together and turned by the front
drive shaft of an old car. The slurry then
goes into concrete mixers, where fibre such
as pampas grass and wood shavings are
added. There’s no specific ratio, says Grant.
It’s a pretty organic process.
From there the mixture goes into a
bread tray and then is packed and tamped
into various different moulds. A group can
make 1000 blocks a day, which are placed
under cloche frames to speed up the drying
process. A finishing plaster is added and
packed into areas of shrinkage.
In the yard they make a whole timber
wall frame with studs and noggins. The
frame is laid on the ground, packed with
light earth blocks held in place with bamboo
slats, and dried before being erected as part
of a small building. A finishing plaster is
then put on. Grant has a portable sawmill
so he can mill local logs.Above: Lisa and Alice with a light earth building in Ruatoria that’s used as a sleepout. It’s warm in
winter and cool in summer. Note the generous eaves.Above: 7KHKņQJLEDVNHWVDUHLQVLGHWKLVXPX
or earth oven. The oven door is wrapped with
a wet sack.Above: Coloured glass bottles make beautiful
features in a light earth wall