light earth (’leichtlehm’) - process
nzeb use a light earth infill consisting of ‘race pumice’ or ‘wood chips’ and selected loams.
these material combinations were very successfully used on previous projects in Mangawhai, Kaiwaka, Matakana and Sandspit.
they produced appealing, stable walls with excellent thermal properties.
the quarried race pumice has an aggregate size varying from 8 to 55mm.
the wood chips are bark free shredded waste wood and /or macrocarpa wood shavings and sawdust.
suitable loam can often be found on site or close proximity. a clay content of about 30% is ideal for the light earth method. the clay merely acts as an adhesive to hold the airpocket-forming aggregates together. the loam is soaked and agitated before mixing it at a ratio of approx. 20% loam to 80% pumice or wood chips in a two arm mixer. the mix is then poured into a temporary shuttering system between the upright members of the frame (posts or studs). the mix is lightly tempered by hand and lateral support is provided by horizontal laths at regular intervals. when dry the walls will have a density of approx. 450-750 kg/cubicmetre, which together with the internal and external plasters will produce an r-value of approx. 1.2 sqm*K/W for the 200mm wall thickness. temperature recording of our projects in Mangawhai and Sandspit over the winter period has confirmed the good thermal properties.
the inside room temperature of the unheated and uninhabited building never dropped below 14 degrees celsius, even when outside frosts were recorded.