AMCER GUIDELINES FOR BUILDING WITH EARTH

DEFINITIONS:

  1. AN EARTH BRICK
    A brick comprising of granular components held together by clay colloidal attraction.
  2. A SEMI-STABILISED EARTH BRICK
    An Earth Brick in which the colloidal attraction is enhanced, strengthened or otherwise improved by admixture(s).
  3. A STABILISED EARTH BRICK
    An Earth Brick in which additives prevent the ingress of water to clay colloids.
  4. An ADOBE OR PUDDLED BRICK
    An Earth Brick produced by adding water to the soil until sufficiently plastic to mould into a brick by hand or sufficiently liquid to flow into a mould.
    These may also be semi-stabilised or stabilised.
  5. A PRESSED EARTH BRICK
    An Earth Brick moulded by applying mechanical or hydraulic pressure to soil with an optimum amount of water for maximum compaction. These may also be semi-stabilised or stabilised.
NOTE: If a brick is held together by other than colloid attraction, a number of factors may change, showing that functionally it is not an Earth Brick
  1. The thermal resistance of the brick may decrease
  2. The brick would not be plastic under stress
  3. The porosity of the brick may increase

ACCEPTABLE PERFORMANCE OF EARTH BRICKS:

  1. Bricks should endure normal temperate rain on a vertical surface without physical protection or surface treatment.
  2. All bricks should have a modulus of rupture (M.O.R.) of at least 150 Kpa, regardless of their intended use as loadbearing or non-loadbearing.

SUITABLE SOILS

  1. Mechanical and chemical analysis is not sufficient to determine a suitable soil for earth wall construction. Test bricks must be made using intended production procedures, and tested for strength and durability.
  2. Soils should be composed of a good grading of 20 mm. minus stone, gravel, sand and silt with enough clay to coat all particles and fill the remaining voids with a slight excess.

TESTING OF BRICKS:

  1. DURABILITY OF BRICKS
    Bricks should be tested for durability by a drip or trickle test, which can be replicated in the field and demonstrate:
    1.  erosion by the size and depth of pitting
    2.  structural weakening and potential erosion by depth of softening
    3.  porosity by width and depth of infiltration
    4.  growth or expansion by measurable welt or swelling
    5.  growth or expansion by cracking after drying out
  2. STRENGTH OF BRICKS
    Bricks should be tested for strength by a modulus of rupture test that can be easily replicated in the field.

NOTE: See Testing Procedures.

SIZE OF BRICKS:

  1. Dry bricks should not weigh more than 15 kilograms.
  2. Bricks should have one dimension to achieve at least a 250 mm. single skin wall.

LAYING OF BRICKS:

NOTE: Mortar joints should be of similar material to the bricks to achieve sufficient bonding to produce a homogeneous wall with uniform surface durability.
  1.  MORTAR BEDS
    1.  Mortar beds should be the minimum required to accommodate the irregularities of the bricks plus the maximum aggregate size in the mud mortar.
    2.  Mortar beds should be the full width beds and finished as struck or flush.
  2.  MUD MORTAR
    1. Mud mortar should be of similar material to the bricks screened to 12 mm. minus. 
    2. Screening may raise the effective clay content. 
    3. Sand may be added to clayey soils to reduce cracking and shrinkage.

 LOAD BEARING WALLS

  1. 250mm. should be the minimum wall thickness.
  2. Wall thickness, roof fixing and positioning of corner, intercepting and buttress walls should be adequate to withstand reasonable wind design loads. 
  3. Unstabilised Earth Bricks should not be used below the following points:
    1. 150 mm. above the external finished grade.
    2. 75 mm. above any floor on ground.
  4. A windmoulding strip should be fixed to all window frames, door frames and posts adjoining the walls.
  5. At least one 230 mm. gal. frame tie, every 3 courses, should be attached to all adjoining frames and posts.
  6. Expansion joints are not necessary for earth walls.
  7. An earth wall does not need a cavity as it is not porous and a solid 250 mm. wall has a sufficient "thermal lag" or "effective R value" for most climates.
  8. It is recommended to use 250x100x3mm Duragal wearing plates on the earth walls beneath rafters or roof beams.
  9. Use mortar mix to mud over chases and reveals for a uniform surface.
NOTE: A 250 mm. minimum wall thickness is recommended not for structural considerations alone. It also gives the minimum "thermal lag" necessary for external walls and sufficient thermal mass for internal walls for most climates.

BRICK TESTING PROCEDURES

  1.  (a) DRIP TEST: The brick is placed with the face at 30 degrees from horizontal and 100 ml. of water is dripped from 400 mm. above the middle of the brick face. After 30 minutes the following measurements are taken:
    1. The depth of the pit where the drips struck the brick.
    2. The depth of softening measured by pushing a 75 x ? mm. nail into the brick by hand, 50 mm. below the pit.
    3. The height of any welt or swelling of the wet area above the original dry surface of the brick. This is best measured just above the pit.
    4. The depth and width of infiltration of water after breaking the brick across the middle.
    5. The extent of any cracking after drying.
      • The maximums for a durable brick should be:
        •  depth of pit 5 mm.
        •  depth ot softening 5 mm.
        •  Height of welt 0.5 mm.
        •  Depth of infiltration 20 mm.
      • NOTE: the brick is porous if water does not reach lower edge of the brick.
  2. SWINBURNE EROSION TEST
  3. MODULUS OF RUPTURE TEST
    1. The minimum M.O.R. should be 150 Kpa
  4. CSIRO ACCELERATED EROSION TEST