There are 5 of these at Vallis Clausa and they are drilled into granite by hand. In these stacks about 15kg of rags mixed with water are turned into a paste, passing from one trough to another. For each stack there are 3 mallets which strike alternately and mix the paste. In the hollow a wooden plate (at the back) and a steel plate (which rests upon the wooden plate) have to endure hours of pounding under the mallet. In the stack, the water circulates continuously. A sort of sluice gate, known as the ‘kas' lets the dirty water from washing the rags out. Crushing in the mallet stack room lasts between 24 and 36 hours.