The focus of Chapter 3 is on the material characteristics of traditional and alternative wall systems.
Methods of constructing walls of adobe, rammed earth and straw bale are presented and illustrated in depth.This chapter also reviews options for foundation and roof systems, which are essential considerations in the design of wall systems.
Foundation systems considered include traditional stone foundations and contemporary concrete foundations, as they apply to the design and construction of
walls of alternative materials.
Roof systems discussed include structural framing options, as well as choices for roof coverings.The review of foundation and roof systems is necessarily limited in scope, as the emphasis of this special study is on alternative and vernacular materials.
Conventional foundation and roof systems are widely employed in contemporary construction and are widely known and understood.
Hence, less detail is given here on such topics as concrete
Such commonly-used materials are the topic of numerous publications and are widely accepted by building code of cials throughout the Southwest.Diagrammatic wall sections are included to illustrate the assembly of adobe, rammed earth and straw bale wall systems.
These sections are for general reference only, and should not be applied to speci c projects without review by design and building professionals in the locale of the contemplated project.
Site analysis is an integral part of the design process, and adaptations may be necessary to address soil conditions and wind or snow loads pertaining to the project location.82 wall systems ADOBE85Cement stabilized adobe wall under construction.
Mud mortar has same percentage of cement content as adobe bricks.
Straw is added as a nod to tradition.
Note 3/8 diameter steel reinforcing bars placed in mortar joint, where a window sill is to be located and additional tensile strength is desired to prevent cracking.
Photo: B.Vint In the making of adobe, earth (composed of sand, silt, and clay) is mixed with enough water to make a stiff mud, which is placed in forms to mold bricks.
The bricks, once removed from their molds, are allowed to dry slowly and bake in the sun over several weeks, being turned and stacked to expose complete drying and curing.
Factors such as drying time.
Anyone having spent time in the desert will understand that it really is possible to bake bricks in the sun: the intense sunlight and heat act to harden the mud in a way not possible in cooler, wetter climates.
Adobe is truly a material of and for the desert.A range of sand, clay, and silt is necessary for good adobe soil.
Sand grains and silt act as aggregate and ller, while clay is the binder.
A wide range in percentages of binder to aggregate can work to produce adequate adobes
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There are both scienti c and intuitive methods for testing the suitability of soil for adobe, which are well-described in the late P.G.Buzz McHenrys book, Adobe and Rammed Earth tests (often taste, touch, on experience to tell if the dirt of a given site is suitable, while geotechnical labs measure particle size distribution, consolidation, compressive and tensile strength, and water absorption through testing.Many types of soil make good adobes.
Fine soils with a high silt content make dense blocks, and require relatively less clay binder GRAVEL
.16 in.FINE GRAVEL
2 mm - 4 mm
- .16 in.COARSE SAND
500 microns - 2 mm
- .08 in.FINE SAND
250 microns - 500 microns
.01 - .02 in.FINES
in.Courtesy of Pattison-Evanoff Engineering, Tucson, AZREGIONAL APPROPRIATENESS86than sandy soils.
Sandy or gravelly soils can work as well, if they have an evenly graded distribution of particle size.
Around the world are found endless variations of Traditional adobe makers add chopped straw to their mix for several reasons:
rst, straw of straw results in a lighter-weight adobe, by increasing the air space in the earth matrix; and third, straw retains moisture to slow drying time for a more uniform curing period, thereby reducing shrinkage cracks as the material dries.
This is analogous
bers to concrete for the same reasons, as is commonly done in contemporary practice.Adobe blocks range from 3 to 4 inches in thickness, from 8 to 14 inches in width, and from 16 to 18 inches in length.
A common is
4H x 12W x 16L , nominal meaning that the dimension includes the thickness of mortar joints, which vary from 3/4 to 1 thick.
Mortar for laying adobe should be mixed from the same materials used in making the blocks to ensure compatibility in terms of hardness, moisture absorption, thermal movement, etc.
Horizontal joint reinforcement of steel wire should be installed at intervals to provide a measure of tensile strength along the wall.There are commercial adobe manufacturers across the American southwest in California, Arizona, New Mexico, Texas, as well as unstabilized block are requested for historic preservation projects, contemporary manufacturers in the U.S.stabilize their product with Portland cement or asphalt emulsion.
Percentages of stabilizer vary with the locale and manufacturer, from
ve percent to ten percent by volume.
Stabilized adobes are protective plaster coating.in large quantities in Mexico, but U.S.building codes require that walls made from which ironically is an incompatible
nish for unstabilized adobe, damaging the adobe over the long term: a reminder that building codes are not infallible.A 20th century innovation in adobe making is the pressed earth block.
These can be produced either manually with a brick press, such as the Cinva Ram, or mechanically