ACT Mud Walls key terms

Choosing the soil layer beneath the topsoil as wall material, rejecting organic-rich, mica-heavy or strongly expansive deposits and preferring gritty, well-graded soils that compact firmly and shrink little on drying.

Removing the upper humus-bearing layer before digging wall material, because decaying plant matter weakens bonds, attracts termites and causes uneven shrinkage and cracking in the finished wall.

A quick field or laboratory test, such as a bottle-shake or colour comparison, confirming that borrowed soil contains no decaying plant matter capable of weakening the wall.

The proportions of gravel, sand, silt and clay in a soil, found by sieving and sedimentation, which govern workability, compacted strength and shrinkage of an earth mix.

The moisture contents marking the boundaries between solid, plastic and liquid behaviour in fine-grained soil, showing how much water a soil tolerates before it becomes unworkable.

The gap between a soil's liquid limit and its plastic limit; a wide gap signals clay-rich material prone to swelling and shrinkage, which is less suitable for unstabilised walls.

A standard laboratory test in which soil is compacted into a mould in layers with a fixed number of blows, relating dry density to moisture content and locating the optimum moisture content.

The mass of solid soil particles per unit volume of compacted material, the main measure of how thoroughly a wall mix has been densified on site.

The weight of cement, lime or other stabiliser expressed as a percentage of the oven-dry weight of soil, the standard way of specifying and checking a mix.

Mixing a measured proportion of Portland cement into moist soil and compacting it before setting begins, giving a stronger, more water-resistant material for walls and foundations.

Adding hydrated or quicklime to clayey soil, where it flocculates the clay, lowers plasticity and slowly raises strength; it works poorly in clean sands.

A binder such as cement, lime, gypsum or bitumen added in small proportions to soil to raise strength and, especially, resistance to softening and erosion by water.

The water content at which a soil reaches its greatest dry density under a stated compaction effort; both drier and wetter mixes end up weaker and more porous.

Measuring and adjusting the water in a batch, by drop test, hand squeeze or moisture meter, so the soil compacts densely without slumping or sticking to tools.

A field check in which a ball of mixed soil is dropped from about one metre; crumbling means too dry, flattening means too wet, and slight deformation suggests correct moisture.

Temporary rigid panels of timber, plywood or steel that hold freshly placed earth in position and shape it until compaction is complete and the material can stand alone.

Oil, grease or thin clay slurry brushed on the inside faces of shuttering so earth does not stick and the form lifts away without tearing the wall face.

A reusable box or frame, often with a removable base or lid, used to shape individual earth blocks or to form a repeated wall section in place.

A horizontal layer of earth or blocks of uniform thickness running along the wall, placed and compacted as one unit before the next layer begins.

The depth of a single layer of loose earth placed before compaction, kept small, commonly 100 to 150 millimetres, so the rammer densifies the full depth.

Densifying loose earth by repeated impact or pressure, driving out air voids and raising dry density, which increases strength and reduces later settlement and water absorption.

A hand tool with a heavy flat or wedge-shaped head, used to strike earth in thin layers until each lift is fully dense before more material is added.

Short natural fibres such as straw, sisal or coir mixed into earth, usually at one to three percent by volume, to restrain shrinkage cracking and add tensile toughness.

The grip and adhesion between successive layers of earth, or between earth and its foundation, obtained by roughening, moistening and compacting the surfaces where they meet.

A laying pattern where each course is offset by half a unit from the course below, so vertical joints never align and loads spread sideways through the wall.

Scoring, stepping or indenting a surface so that the next layer of earth or applied render grips mechanically instead of relying on adhesion alone.

The corner section of a wall, built first and carefully plumbed and levelled, which sets the line, height and thickness for the courses running between corners.

A beam of timber, reinforced concrete or stone spanning a door or window opening, long enough to bear on the wall at both sides and stiff enough to carry the load above.

Keeping new earth or stabilised wall work damp and shaded for a set period so binder reactions finish and early shrinkage cracks are limited.

A protective coating of earth, lime or cement mortar trowelled onto a wall face to shed rain and bridge small cracks, applied in one or more coats.

A continuous water-resistant layer of bitumen membrane, slate or dense concrete built into the wall near ground level to stop moisture rising by capillary action.

A protective capping along the top of a wall that slopes to each side and projects slightly, shedding rainwater clear of the wall faces below.

Progressive removal of wall or foundation material by rain splash, running water or wind, controlled by overhangs, plinths, drains, renders and ground vegetation.

A sloping impervious strip of concrete or stone laid on the ground around the wall base, deflecting falling rain away from the earth foundation.

A gravel-filled trench or perforated pipe at the foot of a wall that collects groundwater and carries it away, keeping the foundation soil dry and stable.

Temporary boards, props or battered slopes supporting the sides of a borrow pit or trench so that soil cannot collapse onto workers below.

Items worn by workers, such as dust masks, gloves, eye protection and safety boots, reducing exposure to silica dust, cuts and crushing injuries on site.

A weighted cord hung freely to define a true vertical, held beside a wall face at several heights to show whether the wall leans.

A long rigid bar held against a wall face or course to reveal high spots, hollows and twisting, so defects can be corrected while the material is still workable.