Terminology

• Stabilized adobe: adobe with emulsified asphalt or Portland cement, up to 10 percent by weight
• Expansive clay: clay that swells and shrinks; no more than half of the clay should be expansive
• Post-and-beam adobe: timber frame with adobe infill, still used in California
• 14.7.4 NMAC: New Mexico adobe code

History and demand

Discovery and early use

• Adobe architecture is dated to before 5,100 BP and was used by Indigenous peoples of the Americas for thousands of years
• The word traces to Middle Egyptian (about 2000 BC); English borrowed it from Spanish in the early 18th century
• Arg-é Bam in Iran, dating to at least 500 BC, is the largest adobe structure

Use in construction

• 1927: the Uniform Building Code was adopted in the United States, leading local rules to limit adobe structures to one story and require seismic design
• 1980s: California Building Code seismic changes effectively ended solid-wall adobe there, though post-and-beam adobe and veneers remain

Composition and production

Raw materials

• Soil with sand, silt, and clay; ideal mix about 15 percent clay, 10 to 30 percent silt, and 55 to 75 percent fine sand (another source gives 15 to 25 percent clay)
• New Mexico State University recommends no more than 1/3 clay, at least 1/2 sand, and no more than 1/3 silt

Product forms

• Bricks typically 10 to 15 kg, up to about 45 kg

Properties

Physical

• Density: about 1,700 kg/m³ (106 lb/ft³)

Mechanical

• Compressive strength: United States building codes generally require at least 300 psi (2.1 N/mm²) for the block

Thermal and moisture

• Thermal conductivity: roughly 0.52 to 0.57 W/(m·K), about 3.6 to 4.0 Btu·in./(h·ft²·°F)
• Specific heat: about 1 kJ/(kg·K)
• Thermal mass: moderates daily temperature swings; R-4.1 to R-10 for a 10 in. wall

Durability

• Seismic: unreinforced adobe is particularly vulnerable; widespread damage in the 1976 Guatemala, 2003 Bam, and 2010 Chile earthquakes
• Moisture: mud plaster, whitewash, or stucco protects walls but needs periodic reapplication; stabilized bricks generally do not need plaster

Uses in buildings

Building elements

• Adobe Walls: load-bearing and infill walls of adobe block, valued for thermal mass; reinforcement and moisture protection govern design
• Wall Cladding: adobe veneers over post-and-beam frames

Pros and cons

Pros

• High thermal mass for hot days and cool nights
• Made from site soil
• Stabilization removes the need for plaster

Cons

• Vulnerable to earthquakes
• Needs plaster maintenance
• Limited to one story under early United States code rules

Sources

• Wikipedia: Adobe, https://en.wikipedia.org/wiki/Adobe