Kiln Loading

Part of Brick Making

Stacking bricks in the kiln for even heat distribution.

Why This Matters

You can have perfect clay, well-made molds, and expertly dried bricks, but if you load the kiln poorly, you will get a mix of overfired bricks near the fire and underfired bricks in dead spots. A badly loaded kiln wastes fuel, wastes time, and can produce 30-50% rejects — bricks too soft for building or too warped to lay flat. In a rebuilding scenario where every resource counts, that waste is unacceptable.

Proper kiln loading is about controlling airflow. Hot gases must reach every brick in the stack at roughly the same temperature and for roughly the same duration. This means creating deliberate channels for heat to flow through, avoiding dense packing that blocks circulation, and placing bricks strategically so the ones that need the most heat get it.

The difference between a skilled kiln loader and a novice shows up immediately in the finished product. A well-loaded kiln produces 90-95% usable bricks with consistent color, ring, and hardness. A poorly loaded one might yield barely half that. Learning to load properly pays for itself within the first firing.

Drying Before Loading

Before any brick enters the kiln, it must be thoroughly dry. Residual moisture turns to steam during firing and causes explosive spalling — bricks literally blow apart, damaging neighboring bricks and potentially collapsing the entire stack.

How to verify dryness:

1. Pick up a brick and hold it against your cheek — a dry brick feels warm or neutral. A damp brick feels distinctly cool.
2. Break a test brick in half and examine the core. A dry brick has uniform color throughout. A damp brick shows a darker center.
3. Weigh a brick, dry it in the sun for another full day, and weigh it again. If the weight does not change, it is dry enough.
4. Tap two bricks together — dry bricks produce a clear ringing sound, damp bricks sound dull and flat.

Minimum Drying Time

Green bricks typically need 7-14 days of air drying in a covered shed before kiln loading. In humid climates, allow 3-4 weeks. Never rush this step. The few days saved are not worth losing an entire kiln load.

General Loading Principles

Create Airflow Channels

The single most important rule: never stack bricks solid. Always leave gaps between bricks for hot gases to circulate. The standard approach is to leave finger-width gaps (10-15mm) between bricks within each row and between rows within each layer.

Orient for Even Exposure

Every brick should have at least two faces exposed to circulating hot gases. Bricks buried deep in a solid pack with only one face exposed will fire unevenly — hard on the outside, soft in the core.

Gradual Density Changes

Pack bricks slightly more densely near the top of the kiln (where heat tends to accumulate) and slightly more loosely near the bottom and around the fire channels. This evens out the temperature distribution.

Weight Distribution

Lower courses support the entire weight above. Use your strongest, driest bricks at the bottom. Never place soft or cracked bricks in the bottom rows — they will crush and the entire stack settles unevenly.

Loading Patterns

The Open Setting (Standard)

This is the most common pattern for updraft and downdraft kilns:

1. First layer — Place bricks on edge (standing on their narrow face) in parallel rows running perpendicular to the fire channels. Leave 15-20mm gaps between each brick and 30-40mm gaps between rows. The rows should align with the fire channels below so heat can rise between them.

2. Second layer — Place bricks on edge at 90 degrees to the first layer, creating a crosshatch pattern. Same spacing rules apply. This cross-layering prevents the stack from leaning and creates vertical as well as horizontal air channels.

3. Third and subsequent layers — Alternate the orientation with each layer. Every odd layer runs one direction; every even layer runs perpendicular.

4. Continue until the kiln is full, leaving at least 150-200mm of space between the top of the stack and the kiln roof (or top of the clamp). This space allows gases to flow over the top of the stack.

The Herringbone Setting

For large kilns where you want maximum density without sacrificing airflow:

1. Set pairs of bricks on edge, leaning against each other at roughly 45-degree angles, forming an inverted V shape.
2. Place the next pair leaning the opposite direction, creating a zigzag pattern.
3. This creates natural triangular air channels between each pair while packing bricks more tightly than the open setting.
4. Alternate the zigzag direction with each layer.

The Finger Setting

For very large bricks or tiles:

1. Stand bricks upright on their narrowest edge in single rows.
2. Space them one finger-width apart.
3. Run every other row perpendicular.
4. This maximizes exposed surface area at the cost of lower packing density.

Loading by Kiln Type

Clamp Kiln (Open Stack)

A clamp is essentially a self-contained stack of bricks that serves as both kiln and product. Loading is the kiln construction:

1. Build the fire channels. Lay the first course of bricks to form parallel tunnels about 300mm wide and 300mm tall, spaced 400-500mm apart. These will hold your fuel.
2. Fill the channels loosely with fuel — brushwood, coal, or dried dung. Do not pack tightly; air must flow through.
3. Stack the bricks above using the open setting pattern. The first few layers above the fire channels should have extra spacing for heat penetration.
4. Taper the stack slightly inward as you build up, creating a roughly domed profile that sheds rain.
5. Seal the exterior with a layer of previously fired bricks or a thick coat of mud. Leave ventilation holes at the base and top that you can plug or open to control airflow.

Updraft Kiln

1. Fire grate or floor — The floor has openings or channels where fire enters from below. Place the first course of bricks on edge, spanning across these openings so heat can rise through.
2. Build up with open setting — Cross-layer as described above. Leave slightly larger gaps in the lower third where heat is most intense.
3. Pack more densely toward the top — The upper third can have slightly tighter spacing since heat rises naturally and the top tends to be cooler than the middle.
4. Leave the center accessible — In round updraft kilns, avoid packing the very center too tightly. Heat enters from the perimeter, and the center is always the hardest spot to fire evenly.

Downdraft Kiln

Downdraft kilns pull heat up and over a bag wall, then down through the stack to a floor-level flue. Loading differs significantly:

1. Do not block the bag wall gap. The bag wall stands between the firebox and the ware. Leave a clear gap of at least 200mm between your stack and the bag wall so heat can rise freely.
2. Pack more loosely at the top. Heat flows over the top of the bag wall and down through the stack. The top needs open channels for the heat to enter.
3. Pack more densely at the bottom. Heat exits through floor-level flues. Denser packing at the bottom slows the heat’s escape, giving it more time to transfer to the bricks.
4. Keep distance from walls. Leave 50-100mm between the outermost bricks and the kiln walls. Heat radiates inward from the walls, and bricks touching the wall will overheat.

Protecting Vulnerable Bricks

Bricks Near the Fire

Bricks closest to the fire channels or firebox receive the most intense heat and are at greatest risk of overfiring. Protect them by:

• Using bricks that have already been fired once (wasters or seconds from previous firings) as sacrificial shields
• Placing your densest, most refractory bricks nearest the fire
• Leaving extra spacing so heat dissipates before reaching the main stack

Bricks at the Top

The top of the stack is exposed to cold air infiltration and radiative heat loss. These bricks often underfire. Mitigate this by:

• Capping the stack with broken bricks or fired rejects that you do not care about
• Sealing the top with a layer of mud or sand to retain heat
• In updraft kilns, partially closing the top opening during the peak firing phase

Corner and Edge Bricks

Bricks at the edges of the stack are exposed to more heat on their outer faces and less on their inner faces. They fire unevenly. Place your less critical bricks (those intended for interior walls or non-structural uses) at the edges.

Loading Capacity and Fuel Planning

A well-loaded kiln packs about 250-350 standard bricks per cubic meter of kiln volume, depending on the setting pattern used. Use this to estimate capacity and fuel needs:

Kiln Volume	Approximate Capacity	Fuel (Hardwood)	Firing Time
1 cubic meter	250-350 bricks	300-500 kg	24-36 hours
5 cubic meters	1,250-1,750 bricks	1,500-2,500 kg	36-48 hours
10 cubic meters	2,500-3,500 bricks	3,000-5,000 kg	48-72 hours
20+ cubic meters	5,000-7,000 bricks	6,000-10,000 kg	72-96 hours

Fuel Staging

Stack your fuel supply in stages near the kiln: Day 1 pile (water smoking, small wood), Day 2 pile (ramp-up, medium wood), Day 3 pile (peak firing, largest and driest wood). Running out of fuel mid-firing is catastrophic.

Common Loading Mistakes

Mistake	Consequence	Prevention
Stacking bricks flat in solid layers	Heat cannot circulate; massive uneven firing	Always set on edge with gaps
Loading damp bricks	Explosive spalling, chain damage to neighbors	Test dryness; extra drying time
Uniform spacing throughout	Top underfires, bottom overfires	Adjust density by zone
Touching kiln walls	Bricks fuse to wall, damage both	Maintain 50-100mm clearance
No sacrificial layer at top	Top course always underfired	Cap with wasters or broken bricks
Leaning stacks	Stack collapse during firing	Cross-layer and check plumb frequently
Blocking fire channels	Fuel starved, firing stalls	Verify clear airflow before sealing

Post-Loading Checklist

Before you light the fire, verify:

1. All bricks are bone-dry (cheek test, break test)
2. Fire channels are clear and loaded with starter fuel
3. The stack has visible air gaps throughout — you should be able to see light through the stack from multiple angles
4. The stack is stable and plumb — push gently on the top. Any wobble means restacking
5. Sacrificial or previously fired bricks protect the bottom, edges, and top
6. Spy holes are clear and unblocked — you need to see fire color during the burn
7. Dampers and ventilation openings are functional and accessible
8. Fuel supply is staged, dry, and sufficient for the full firing cycle
9. The kiln exterior is sealed (clamp) or doors are bricked up (permanent kiln) with mud mortar that can be broken out later