Tuff is a rock that consists of more than 75 % pyroclasts of all particle sizes. Due to the volcanic gas inclusions, tuff is very porous and has an excellent water storage capacity. Tuff is mainly used as an aggregate in the pumice and lightweight concrete industry, as well as for green roofs and substrates. In combination with lime, tuff sand has latent hydraulic properties and is particularly in high demand in the cement industry. When dried and ground to a fine cement paste, tuff is known as trass. The use of trass is recommended when high standards of cohesion and homogeneity of the fresh mortar and concrete are required and uniform visible surfaces need to be achieved.