# How to Build Bricks

Follow one brick from a lump of clay to a wall: mix, mould, dry, fire in a kiln and lay it\.

By vivid\-moon\-0e7f24dd

Topic: Engineering

[Open the interactive Jig](https://ask.jig.com/j/tgvBE5xOn9xl)

## Transcript

### 1. A brick is baked earth

A brick starts as sticky clay dug from the ground\. Shape it, dry it and bake it at about 1,000 °C, and it becomes as hard as stone\. Let's follow one brick from mud to a wall\.

A standard UK brick is 215 × 102\.5 × 65 mm: small enough to lift with one hand\.

### 2. Dig the clay

Clay is a soft earth made of tiny, flat grains\. Brickworks dig it from quarries, layer by layer\. Most clays hold a little iron, and that iron will matter later\.

Clay with about 4–8% iron oxide usually turns red in the kiln\.

### 3. Mix it smooth

The clay is crushed and ground so its grains are even\. Water and sand are mixed in until it feels like stiff dough, soft enough to shape\.

Clay for machine shaping is often about 18–25% water\.

### 4. Shape it in a mould

Make a brick by hand: throw the clay hard into a sandy wooden mould, scrape off the extra with a stick called a strike, then lift the mould away\. A raised block in the mould leaves a dip called the frog\.

Factories squeeze clay through a nozzle and cut it with wires, up to about 25,000 bricks an hour\.

### 5. Dry it slowly

A fresh, soft brick is called a green brick\. Warm air dries it until almost no water is left, and it turns paler\. Dry it too fast and it cracks\.

Factory drying takes about 4 to 45 hours and leaves less than 2% water\.

### 6. Fire it in the kiln

A kiln is a giant oven\. Slide the heat up: past about 500 °C the clay changes for good, and near 900 °C its iron turns it red\. By 1,000 °C the grains start to fuse, making it hard\. Slide it back down: the brick stays changed\.

Firing is one\-way\. A fired brick will never turn back into mud\.

### 7. Cool and check

The kiln car rolls out and the bricks cool down\. They are checked and stacked into cubes, ready for the lorry\. Faulty bricks are crushed and used again\.

Look in a frog: brickmakers often press their name there\.

### 8. Build a wall

A thin layer of mortar sticks each brick to the next\. Each row is shifted by half a brick, so no joint runs straight up the wall\. That bond spreads the weight and keeps the wall strong\.

With a 10 mm joint, each UK brick fills 225 × 75 mm of wall face\.