An ancient technique used in many parts of the world and introduced to NZ by the French missionary settlers. The oldest earth building in NZ is Pompallier house in the Bay of Islands, a rammed earth building built in 1841-2 and still standing today. It was however less common historically in this land than cob or mud brick.
Like adobe and cob it is ideally suited to internal heat sink walls.
Slightly damp earth (dryer than cob) is tamped between shuttering usually with pneumatic rammers. Sand and gravel is added to the soil mix to reduce shrinkage cracking. The formwork can be removed immediately after ramming.
Nowadays it is usually cement stabilised (with around 10% cement added). This modern intervention is not necessarily required though and the wall will have less embodied energy without Portland cement.
Rammed earth is covered in the Earth Building Standards.
● Eaves/ verandahs or rain screen/ cladding required as primary weather protection for durability
● 280-450 thick load bearing
● R value is poor so internal walls are best unless insulated. Natural external insulation can be used with rain screen cladding over. Research is being done on sandwich construction with perlite insulation and with homogenous mixes with pumice or scoria aggregate to reduce density
● Must have control joints
● Can get cement streaking if the wall is cement stabilised
● Nib is required for fixing the boxing
● Joinery can be rebated up to 1/3 of wall thickness
● Services; Electrical conduit can be rammed in. Water pipes can pass through wall (sleeved) but not run in wall due to potential condensation or leakage. They can be surface mounted or run through other walls
● Timber lintels 300-450mm min seating. Concrete lintels 450 min seating
● Timber or reinforced concrete bond beams or ceiling diaphragms are required
● Reinforcing is required in NZ; vertical rods rammed in and sleeved and perhaps horizontal reinforcing depending on earthquake zone and the engineer’s design.
● Foundations, reinforced concrete strip footing required in NZ with damp proofing between the footing and the earth wall
● Joseph M. Tibbets. The Earthbuilders’ Encyclopedia. Southwest Solaradobe School, 1988.
● Joseph F. Kennedy, Michael G. Smith and Catherine Wanek, Editors. The Art of Natural Building Second Edition. New Society Publishers, 2015.
● Gernot Minke. Building With Earth. Birkhäuser Verlag, 2013.