Mold Making

Part of Brick Making

Building wooden brick molds for consistent sizing.

Why This Matters

Without consistent mold sizes, every brick you make is a slightly different shape. When you try to build a wall from irregular bricks, you end up with thick, uneven mortar joints that waste material and create structural weak points. Walls lean, courses do not align, and corners will not meet cleanly. A good mold solves all of this — it produces bricks of uniform dimensions that stack predictably, bond correctly, and create strong, plumb walls.

Mold making is one of the simplest but highest-impact skills in brick production. A single well-made mold can produce thousands of bricks before it wears out. A set of two or three molds allows multiple workers to produce bricks simultaneously, dramatically increasing output. The mold itself costs only a few pieces of straight-grained wood, some nails or pegs, and an hour of careful work.

The investment in getting your molds right pays dividends through every subsequent stage — drying, firing, and laying. Consistent bricks dry at the same rate (fewer cracks), fire at the same rate (fewer rejects), and lay at the same rate (faster wall construction). This is one of those places where an hour of careful preparation saves weeks of frustration later.

Materials and Tools

Wood Selection

Choose straight-grained hardwood for durability. The mold will be repeatedly wetted, filled with abrasive clay, and struck with a stick — softwoods wear out quickly.

Wood Type	Suitability	Notes
Oak	Excellent	Very durable, resists water, widely available
Maple	Excellent	Hard, smooth surface
Ash	Good	Strong but may split at thin sections
Beech	Good	Hard, but swells with moisture
Pine/spruce	Acceptable	Use if hardwood unavailable; will wear faster
Green (unseasoned) wood	Poor	Will warp and shrink as it dries — use seasoned wood

Boards should be 20-25mm thick for the sides and at least 12mm thick for the bottom (if using a bottom plate). Thinner wood warps under repeated wetting.

Tools Needed

• Saw (hand saw, bow saw, or any cutting tool)
• Straight edge or ruler for marking
• Hammer and nails, or chisel and wooden pegs
• Plane or knife for smoothing surfaces
• Square or right-angle reference for checking corners

Single-Brick Mold

The simplest design — an open-topped, bottomless rectangular frame.

Construction Steps

1. Determine your brick size. Standard dimensions are approximately 220mm long x 105mm wide x 65mm tall, but choose dimensions appropriate to your needs. See the companion article on mold sizes for guidance.

2. Cut two side pieces. Each should be the brick length (220mm) plus twice the wall thickness of your mold (2 x 20mm = 40mm), so 260mm long. Height equals the brick height: 65mm.

3. Cut two end pieces. Each should be the exact brick width: 105mm. Height equals the brick height: 65mm.

4. Assemble the frame. Butt the end pieces inside the side pieces so the interior dimension is exactly 220mm x 105mm. The side pieces overlap the end pieces at each corner.

5. Fasten the joints. Use two nails or wooden pegs at each corner. Drill pilot holes to prevent splitting. The joint must be rigid — any play means inconsistent bricks.

6. Check squareness. Measure both diagonals of the interior opening. They must be equal. If not, adjust by tapping the frame until the diagonals match, then fasten firmly.

7. Smooth the interior. Sand or plane all interior surfaces smooth. Any roughness causes clay to stick, making it difficult to release the brick cleanly.

Oiling the Mold

Before each use, dip the mold in water or brush the interior with fine sand. This prevents clay from sticking to the wood. Some brickmakers rub the interior with tallow or oil every few dozen bricks. A well-conditioned mold releases bricks cleanly with a single shake.

Multi-Brick Gang Mold

For higher production rates, build a mold that forms 2, 3, 4, or 6 bricks at once.

Construction Steps

1. Cut two long side pieces. Length equals (number of bricks x brick length) + (number of dividers x divider thickness) + (2 x end overlap). For a 3-brick mold: (3 x 220mm) + (2 x 20mm) + (2 x 20mm) = 740mm.

2. Cut two end pieces at the brick width (105mm) and the brick height (65mm).

3. Cut internal dividers — one fewer than the number of bricks. Same dimensions as the end pieces (105mm x 65mm). These separate the individual brick cavities.

4. Assemble the sides and ends first, then slide in the dividers at equal intervals.

5. Fasten the dividers with nails through the side pieces into the divider ends.

6. Add handles. Nail or peg a handle piece across each end, extending 50-75mm beyond the sides. This makes the mold easy to carry and lift when full of heavy clay.

Gang Mold Advantages

• 3-6x faster production than single molds
• Bricks in the same mold are guaranteed identical in size
• One person can fill and strike a 4-brick mold, then hand it to a second person for demolding while filling the next mold

Gang Mold Disadvantages

• Heavier and harder to handle — a filled 4-brick gang mold weighs 12-15 kg
• If one cavity releases poorly, the whole set is delayed
• Requires more careful construction to keep all cavities truly identical

Bottom Plate Mold

Adding a bottom plate to the mold simplifies the molding process, especially for beginners.

When to Use a Bottom Plate

• When your molding surface is uneven and bricks would have irregular bottoms
• When making bricks with a frog (indentation) in the bottom for mortar keying
• When training new brickmakers who struggle with the bottomless release technique

Construction

Follow the single-mold or gang-mold instructions above, but add a bottom board:

1. Cut a board to match the exterior dimensions of the mold frame
2. Nail or peg it to the bottom of the frame
3. To add a frog, attach a raised wooden block (roughly 100mm x 50mm x 10mm) to the center of the bottom plate. This creates an indentation in the bottom of the brick that improves mortar adhesion.

Release Technique

With a bottom plate, you cannot simply lift the mold straight up — the brick is trapped. Instead:

1. Place the filled mold on a smooth board (the “pallet”)
2. Flip the mold and pallet together upside down
3. Lift the mold frame and bottom plate off, leaving the brick sitting on the pallet
4. Carry the pallet to the drying area

The Molding Process

Preparing the Clay

The clay must be at the right consistency — wet enough to fill all corners of the mold without air pockets, but stiff enough to hold its shape when the mold is removed. Test by squeezing a ball of clay: it should hold fingerprints sharply without cracking at the edges.

Filling the Mold

1. Wet or sand the mold interior to prevent sticking
2. Take a clot of clay slightly larger than the mold cavity — roughly the size of a large grapefruit for a standard brick
3. Slam the clay into the mold with force. Throw it down into the cavity to drive out air pockets. This step matters — air pockets become weak spots or cause cracks during drying and firing
4. Press into corners. Use your thumbs to push clay firmly into all four corners and along all edges
5. Add more clay if needed to overfill the mold slightly
6. Strike off the excess. Draw a straight stick, wire, or taut string across the top of the mold to shear off excess clay, leaving the top perfectly flush with the mold rim. Use a smooth, steady motion from one end to the other. Do not saw back and forth — this drags and deforms the surface

Releasing the Brick

Bottomless mold method:

1. Place the mold on the drying surface (smooth ground, a board, or a sand bed)
2. Lift the mold straight up with a smooth, steady motion
3. The brick should release cleanly and stand on the surface
4. If it sticks, the clay is too wet or the mold needs sanding/oiling

Bottom-plate mold method:

1. Flip onto a pallet board
2. Lift the mold off
3. Carry the pallet to the drying area
4. Slide the brick off the pallet onto the drying surface

Mold Maintenance

Daily Care

• Rinse the mold in clean water after every 20-30 bricks to remove clay buildup
• Re-sand or re-oil when bricks start sticking
• Store molds upright (on edge) so water drains out — never leave them sitting in a puddle

Weekly Inspection

• Check all joints for looseness. Re-nail or re-peg as needed
• Verify interior dimensions with a measuring stick — wood swelling can change cavity size
• Look for cracks in the wood, especially at nail holes. Replace cracked pieces before they fail during production

Extending Mold Life

• Apply linseed oil or tallow to the exterior surfaces to resist water absorption
• Line the interior with thin sheet metal (tin, copper, or iron) if available — this dramatically extends mold life and produces smoother brick surfaces
• Replace worn molds before they produce inconsistent bricks — a mold that is 5mm oversize produces bricks that will not bond properly

Production Rates

An experienced brickmaker with a single bottomless mold can produce 400-500 bricks per day. With a 4-brick gang mold and a helper, output rises to 1,000-1,500 bricks per day. A team of 4-6 people with multiple gang molds can produce 3,000-5,000 bricks per day — enough to fire a clamp kiln every 2-3 days.

Specialty Molds

Wedge Bricks

For arches and curved walls, make molds where one end is narrower than the other. The standard approach is to taper one of the end pieces by 10-20mm. When laid in a curve, the wider face is on the outside of the arc and the narrower face is on the inside.

Half Bricks and Closers

Make a mold the exact width of half a brick (lengthwise) for queen closers, and half the length for half-bats. These specialty shapes are essential for maintaining bond patterns at corners and ends of walls. It is much better to mold them to size than to cut fired bricks, which always risks cracking.

Channel Bricks

For drainage or conduit, create a mold with a semicircular wooden core inserted from one end. After molding, withdraw the core to leave a channel through the brick. These are useful for primitive plumbing and ventilation systems.