Before the ‘green’ clay bricks can be fired in a kiln, the maximum amount of moisture must be removed, otherwise the bricks will explode during the firing process. Drying must be done in such a way that the moisture is evenly removed from the inside out. If the outer faces of the brick are allowed to dry first then water from the inside of the brick cannot escape and remains trapped. Any trapped moisture will be forced out by the high temperatures in the kiln during firing and cracking of the brick is likely to result.
To prevent this, brick-drying chambers are maintained at temperatures of about 80 to 120 degrees centigrade within a very humid atmosphere, which keeps the exterior of the bricks moist. The bricks shrink during the drying process (which can last up to 40 hours) as the clay particles come together, whilst temperature and humidity are closely monitored to minimize surface cracking.