ACT Mud Walls flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Clay as natural binder

In unstabilized earthen walls, clay particles coat and bind the sand and gravel skeleton. Too little clay weakens the mix; too much causes shrinkage cracks during drying.

Rejecting organic topsoil

Topsoil, roots and leaf matter contain organics that prevent clay and cement bonding, so strength drops and walls crumble. Soil with roughly more than 2% organic content is unsuitable.

Plasticity index calculation

Plasticity index equals liquid limit minus plastic limit, both measured on soil passing the 0.425 mm sieve. A high index signals a clay that shrinks and swells strongly.

Proctor test outcome

The Proctor compaction test compacts soil at several water contents and plots dry density against moisture. It identifies maximum dry density and optimum moisture content used for field control.

Cement content for stabilization

Rammed earth is normally stabilized with 4 to 10 percent cement by dry soil mass. Strength gains flatten above roughly 10 percent, so higher doses waste material and cost.

Target rammed earth density

Well-compacted rammed earth reaches about 1800 to 2100 kilograms per cubic metre. In-place density is the main field control parameter because it governs strength, stiffness and durability.

Lime versus cement stabilizer

Lime suits clayey soils and reacts pozzolanically with clay minerals, needing a mellowing period. Cement suits granular soils with low clay and sets quickly once water is added.

Mellowing the soil mix

After water is added, soil is covered and left 12 to 24 hours so dry clay lumps hydrate evenly. Mellowing gives consistent moisture and better compaction than immediate placement.

Set time after mixing cement

Cement-stabilized soil must be placed and compacted within roughly 60 to 90 minutes of adding water. Re-tempering a stiffened mix with extra water lowers final strength.

Sugars and organic retarders

Sugars, oils and organic acids retard or stop cement hydration. Water carrying more than about 0.5 percent sugar relative to binder mass should not be used for stabilized earth.

Formwork release agent

A thin coat of vegetable oil, mould oil or soap solution on clean form faces stops soil sticking. Without it, ramming tears the wall face when forms are stripped.

Typical formwork panel height

Rammed earth forms are usually 1.0 to 1.5 metres tall, matching about one day of placement. Forms are stripped and raised once the lifts below have stiffened.

Tie rod spacing in forms

Form panels are tied or clamped at roughly 600 to 900 millimetre centres to resist lateral pressure from ramming. Closer spacing is needed for tall or narrow forms.

Compacted lift thickness

Each rammed layer is placed loose at about 150 to 200 millimetres and compacted to roughly 100 to 150 millimetres. Thicker lifts stay loose at the base.

Wall slenderness limit

Unreinforced earthen walls should keep height-to-thickness ratios within about 10 to 12. A 300 millimetre thickness is a common minimum for loadbearing external walls.

Plinth above ground level

Earthen wall bases are raised 150 to 300 millimetres above external ground on a plinth with a damp-proof course, so capillary water and splash cannot reach the wall.

Loose to compacted ratio

Rammed earth typically shrinks from loose to compacted volume in a ratio of about 1.4 to 1.6 to 1, which converts loose soil volumes into finished wall volumes.

Ramming pattern in lift

Ramming begins at the formwork edges and progresses toward the centre, each pass overlapping the last. Edge-first patterns prevent loose zones along the finished face.

Rebar cover in earth

Steel reinforcement in earthen walls needs at least 25 to 50 millimetres of cover and should sit in the middle third, otherwise rust staining and spalling follow.

Bamboo reinforcement treatment

Bamboo used as reinforcement is seasoned, coated with bitumen or borate preservative against rot and insects, and lapped generously. Untreated bamboo swells and loses bond.

Bonding successive lifts

A dried lift surface is scarified about 5 to 10 millimetres deep, moistened, and coated with cement or clay slurry immediately before the next lift is placed.

Block mortar joint thickness

Compressed earth block walls use joints typically 10 to 12 millimetres thick with cement-sand, soil-cement or lime mortar. Head joints are staggered by at least a quarter block.

Lintel bearing length

Lintels over openings need at least 200 to 300 millimetres of bearing on the wall at each end. Openings narrower than about 600 millimetres may use a flat lintel.

Ring beam purpose

A continuous reinforced concrete or timber ring beam at the top of earthen walls ties walls together, spreads roof loads, and limits differential movement and cracking.

Curing stabilized rammed earth

Cement-stabilized earth is kept damp and covered for about seven days after compaction. Moist curing supports hydration; premature drying leaves weak, dusty surfaces.

Why avoid cement plaster

Cement-rich render is rigid and nearly impermeable, so it cracks and traps moisture inside earth walls. Clay or lime plasters stay breathable and tolerate small movements.

Minimum roof overhang

Roof eaves should extend at least 500 to 600 millimetres beyond the wall face, and more on windward sides, to keep driving rain off the earth surface.

Ground slope away from walls

Finished ground should fall away from the building at about 2 percent, or 1 in 50, for at least 3 metres, preventing ponding and splash erosion at the wall base.

Silica dust control

Dry soil handling releases respirable crystalline silica. Control it with water suppression or extraction, and wear at least a P2 or N95 respirator during dusty tasks.

Manual rammer weight

Hand rammers typically weigh 6 to 10 kilograms and are lifted repeatedly. Task rotation and shared lifting of form panels reduce back and shoulder injury on site.

Oven dry moisture content

Moisture content equals wet mass minus dry mass, divided by dry mass, times 100. The sample is dried at 105 degrees Celsius to constant mass, usually overnight.

Wall plumb tolerance

A finished earthen wall should be plumb within about plus or minus 10 millimetres over a 3 metre height, checked with a spirit level or plumb bob.