Brick Making

Why This Matters

Bricks are the foundation of permanent civilization. Unlike wood, bricks do not rot, burn easily, or attract insects. A community that can produce consistent, strong bricks can build structures that last centuries — walls, ovens, kilns, chimneys, aqueducts, and fortifications that no other building material can match without advanced technology.

Finding and Testing Clay

Brick making starts with clay. Not all soil contains enough clay, and not all clay makes good bricks. You need to find the right material and test it before committing to production.

Where to Find Clay

Clay deposits are common near:

• River banks and flood plains — sediment deposits often contain excellent clay
• Hillside cuts and road embankments — exposed layers reveal clay seams
• Pond and lake beds — dried-up bodies of water often have thick clay floors
• Below topsoil — dig 30-60 cm down in many areas to hit clay subsoil

Clay feels smooth and sticky when wet, and cracks into hard chunks when dry. If soil feels gritty, it is mostly sand and unsuitable.

Testing Your Clay

Before making hundreds of bricks from bad clay, run these quick tests:

Ribbon Test

1. Wet a lump of clay until workable
2. Roll it into a cylinder and flatten it
3. Squeeze it between thumb and forefinger, pushing it out into a flat ribbon
4. Good brick clay forms a ribbon 5-8 cm long before breaking
5. Too short (< 3 cm) = too much sand. Too long (> 10 cm) = too fat, will crack

Drop Test

1. Form a ball of clay about 5 cm diameter
2. Let it dry completely (2-3 days)
3. Drop it from waist height onto hard ground
4. If it shatters — too much sand. If it holds together — clay content is adequate

Shrinkage Test

1. Fill a mold 20 cm long with wet clay
2. Mark the exact length
3. Let it dry completely, then measure again
4. Shrinkage over 8% means the clay is too fat — add sand
5. Ideal shrinkage: 4-6%

Tempering Fat Clay

If your clay is too “fat” (high clay content, excessive shrinkage), add sharp sand at 20-30% by volume. Mix thoroughly when wet. If too “lean” (too much sand), add pure clay or soak and screen to remove coarse particles.

Preparing Clay

1. Soak dry clay in water for 24-48 hours until fully saturated
2. Screen through a coarse mesh to remove stones, roots, and debris
3. Wedge by kneading like bread dough — fold, press, turn, repeat 50+ times
4. This removes air pockets that cause bricks to explode during firing

Mud Bricks (Adobe)

The simplest brick requires no kiln at all. Adobe bricks are sun-dried and have been used for thousands of years in arid climates.

The Adobe Mix

The ideal adobe mix is:

• 60-70% sand (sharp, coarse sand is best)
• 30-40% clay
• Straw or grass chopped to 5-10 cm lengths, roughly a handful per brick

Component	Purpose
Clay	Binder — holds everything together
Sand	Prevents cracking during drying
Straw	Reinforcement — adds tensile strength, controls shrinkage
Water	Makes the mix workable

Mix in a pit or trough: add water gradually, stomp with feet or mix with a hoe until the consistency is thick mud that holds its shape when squeezed.

Making Molds

Build wooden molds from scrap lumber:

1. Cut four pieces to form a rectangular frame (no top or bottom)
2. Standard brick size: 25 x 12 x 8 cm (adjust to your needs)
3. Double or triple molds speed production
4. Soak molds in water before use so clay releases cleanly

Molding Process

1. Wet the mold and place on flat, dry ground (a board or packed earth)
2. Throw a handful of sand inside to prevent sticking
3. Pack the adobe mix firmly into the mold, pressing into corners
4. Strike off the top level with a stick or board
5. Lift the mold straight up — the brick stays on the ground
6. Repeat, spacing bricks 5 cm apart for air circulation

Drying

1. Leave bricks flat for 2-3 days until firm enough to handle
2. Stand them on edge and dry for another 5-7 days
3. Stack loosely in a covered area for final curing — at least 2 more weeks
4. Total drying time: 3-4 weeks minimum

Rain Destroys Adobe

Wet adobe bricks dissolve. If rain threatens during drying, cover immediately with tarps, large leaves, or boards. Finished adobe walls also need protection — deep roof overhangs or plaster coating.

Pressed Earth Bricks (Compressed Earth Blocks)

Pressed earth bricks are stronger than adobe because mechanical pressure compacts the soil more tightly than hand-packing.

The Press

A simple lever press can be built from wood and iron:

1. Build a sturdy wooden frame bolted to a base
2. The mold box sits at the bottom — same size as your desired brick
3. A lever arm (2 meters long) drives a piston down into the mold
4. Body weight on the lever produces roughly 2-4 MPa of pressure

Mix and Process

1. Use a drier mix than adobe — damp but not wet (squeeze test: holds shape, no water drips)
2. Mix: 70% sandy soil, 25% clay, 5% cement or lime (if available — optional but greatly increases strength)
3. Fill the mold box, level off the top
4. Pull the lever to compress
5. Eject the brick by releasing the base plate
6. Cure for 7-14 days, keeping moist (spray with water daily if using cement)

Fired Bricks

Fired bricks are the strongest and most durable. Firing transforms clay minerals permanently — once fired, a brick will never dissolve in water.

Forming Bricks for Firing

Use a leaner mix than adobe (little or no straw — it burns out and leaves voids):

• 70% clay
• 30% sand
• No organic matter

Form using the same mold process as adobe, but with tighter packing. Each brick must be uniform in size and density for even firing.

Drying Green Bricks

Green (unfired) bricks must be bone-dry before kiln loading:

1. Air-dry for 1-2 weeks, turning regularly
2. Move to a covered, ventilated area for final drying
3. Any moisture in a green brick will turn to steam in the kiln and shatter it
4. Test: a dry brick feels warm to the touch (wet bricks feel cool)

Never Rush Drying

Cracking during drying means your clay is too fat (add sand) or you are drying too fast (slow down, add shade). Every cracked brick is wasted fuel and labor in the kiln.

Kiln Firing

Clamp Kiln (No Permanent Structure)

The clamp kiln is a temporary arrangement of bricks and fuel stacked in the open, then set alight. It is the simplest way to fire bricks and requires no pre-existing kiln.

Building the Clamp

1. Choose a flat, wind-sheltered site
2. Lay a foundation layer of fuel (wood or charcoal) on the ground
3. Stack green bricks in a grid pattern with 2 cm gaps for airflow
4. Every 3-4 layers, add another thin layer of fuel (charcoal works best)
5. Build the stack 1-2 meters high, tapering slightly inward
6. Cover the outside with a layer of fired bricks (if you have them) or a thick coat of mud
7. Leave fire holes at the base on the windward side

Firing Schedule

1. Smoking phase (12-24 hours): Small fires at the base, just enough to produce steam and drive out remaining moisture. Go slow.
2. Full fire (24-48 hours): Build fires to full intensity. The interior should glow red (900-1000 C).
3. Soaking (6-12 hours): Maintain peak temperature.
4. Cooling (3-5 days): Let the clamp cool completely. Do not open early — thermal shock cracks bricks.

Firing Stage	Duration	Temperature	Signs
Smoking	12-24 hours	100-300 C	Steam from vents
Ramp up	6-12 hours	300-600 C	Smoke thins, heat intensifies
Full fire	24-48 hours	900-1050 C	Red/orange glow visible in gaps
Soaking	6-12 hours	1000-1050 C	Steady glow throughout
Cooling	72-120 hours	1050-ambient	Gradual, no intervention

Fuel Requirements

Expect to use roughly 1 cubic meter of wood per 1,000 bricks. Charcoal is more efficient and produces more even heat. A clamp kiln of 500 bricks is a good starting batch.

Updraft Kiln (Permanent)

Once you are producing bricks regularly, build a permanent updraft kiln:

1. Dig a firebox trench (1 m wide, 0.5 m deep) below ground level
2. Build walls from already-fired bricks, forming a chamber 1.5 x 1.5 x 1.5 m
3. The firebox feeds heat through channels in the floor
4. Load green bricks inside with gaps for heat circulation
5. Cover the top with broken brick and mud (leave vent holes)
6. Fire from below — heat rises through the load

An updraft kiln uses 30-40% less fuel than a clamp kiln and produces more consistent results.

Brick Bonds and Mortar

Common Bond Patterns

Bond	Pattern	Strength	Use
Stretcher	All bricks lengthwise, staggered	Moderate	Partition walls (half-brick thick)
English	Alternating rows of stretchers and headers	Very high	Load-bearing walls
Flemish	Each row alternates stretcher-header	High	Strong and attractive
Header	All bricks end-on	High	Curved walls, arches

Mortar

For mud bricks, use mud mortar (same mix as the bricks, minus straw). For fired bricks, lime mortar is far superior:

• Mud mortar: 1 part clay, 2-3 parts sand, water to paste consistency
• Lime mortar: 1 part slaked lime putty, 3 parts sand (see Lime and Cement)

Apply mortar 10-15 mm thick. Press each brick firmly and check level with a straightedge. Mortar joints should be consistent throughout the wall.

Quality Testing

The Ring Test

Tap two fired bricks together. A clear, metallic ringing sound indicates complete firing. A dull thud means underfired — the core is still soft clay.

Absorption Test

1. Weigh a dry brick
2. Soak it in water for 24 hours
3. Weigh again
4. Water absorption should be under 20% for a good fired brick
5. Over 25% means underfired or poor clay mix

Scratch Test

Scratch the surface with a nail. A well-fired brick resists scratching and does not crumble. If the nail digs in easily, the brick needs higher firing temperature.

Compression

A well-made fired brick should survive being stood on by an adult without cracking. For structural use, you want bricks that can bear at least 5 MPa (roughly a car’s weight on a single brick).

Your First Batch Will Be Imperfect

Expect 20-30% waste on your first clamp firing — some underfired, some cracked, some warped. Use these rejects as aggregate (grog) crushed into your next batch’s clay mix, or as kiln furniture. Every batch teaches you about your specific clay and fuel.

What’s Next

With reliable bricks, you can build far more ambitious structures:

• Structural Engineering — arches, vaults, and multi-story buildings become possible
• Lime and Cement — combine with brick for waterproof, load-bearing masonry
• Build kilns, furnaces, and forges that enable Metalworking and Glassmaking

Brick Making — At a Glance

Clay testing: Ribbon test (5-8 cm), drop test (holds together), shrinkage under 8% Adobe bricks: 60-70% sand + 30-40% clay + straw, sun-dry 3-4 weeks Fired brick mix: 70% clay + 30% sand, no organics Green brick drying: Must be bone-dry before firing (1-2 weeks minimum) Clamp kiln: Stack bricks with fuel layers, fire 2-4 days at 900-1050 C, cool 3-5 days Updraft kiln: Permanent structure, 30-40% less fuel, more consistent results Quality checks: Ring test (clear sound), absorption under 20%, scratch resistance Mortar: Mud mortar for adobe, lime mortar for fired brick (1:3 lime:sand) Expect: 20-30% waste on first firing, improves with practice