Ferrocement / Thin-Shell Concrete — FarmPal

Thin layers of cement mortar applied over a mesh of closely-spaced steel reinforcement, creating incredibly strong curved surfaces. Used for dome homes, water tanks, boats, and roofing. Extremely strong for its thickness.

History

Invented in 1848 by Joseph-Louis Lambot. Used extensively by Pier Luigi Nervi for stunning architectural structures. Steve Kornher popularized ferrocement domes for affordable housing.

Cost/sq ft
$15-$50
Build Time
6-16 weeks
Crew Size
2-6 people
DIY Friendly
Yes ✓
Code Compliance
moderate
Thermal Mass
medium
R-Value
R-1 per inch (must add exterior insulation for cold climates)
Lifespan
200+ years

Best Climates

all climates (with insulation)

Resistance Ratings (1-5)

tornado★★★★★
hurricane★★★★★
earthquake★★★★★
fire★★★★★
flood★★★★★
mold★★★★☆
termites★★★★★
bullets★★★★☆

Materials

Rebar (3/8" and 1/4")
Welded wire mesh
Chicken wire/expanded metal lath
Portland cement
Sand
Tie wire
Spray foam insulation (exterior)

Build Steps

  1. 1Build rebar armature in desired dome/vault shape
  2. 2Attach welded wire mesh to rebar frame on both sides
  3. 3Add chicken wire or expanded metal lath over mesh
  4. 4Apply first coat of cement mortar from inside (mortar stays put against mesh)
  5. 5Apply remaining coats in thin layers (total wall thickness 1.5-3")
  6. 6Cure properly keep moist for 7+ days
  7. 7Waterproof exterior with elastomeric coating
  8. 8Apply rigid foam insulation to exterior for thermal performance
  9. 9Apply finish coat over insulation
  10. 10Interior can be plastered or painted directly

✓ Pros

  • •Incredibly strong
  • •Any shape possible
  • •All-hazard resistant
  • •No formwork needed
  • •Thin walls save space
  • •Versatile roofs, walls, tanks

✗ Cons

  • •Needs insulation in most climates
  • •Cement carbon footprint
  • •Skill required for thin, even application
  • •Curved surfaces harder to furnish

⚠️ Warnings

  • •Insulation must be added for thermal comfort in most climates
  • •Cement production has high carbon footprint offset with longevity
  • •Proper curing is critical keep walls moist for at least a week
  • •Work in thin layers thick applications slump and crack