What makes one brick tougher than another? The size of the sand grains mixed into the clay affects how well the brick holds together after firing. You make two batches of five bricks each. One batch uses fine sand mixed with clay. The other uses coarse sand. Both use the same ratio and the same amount of water. After drying for two days, you fire the bricks in an oven at 900 degrees Celsius for 24 hours. Then you drop each brick from a height of 2 meters and count how many drops it survives. Coarse-sand bricks last an average of 2.6 drops. Fine-sand bricks last only 1.6 drops. Coarse grains produce a more durable brick.