In mural constructions the mortar has to distribute the weight between the load-bearing blocks as uniform as possible and to unite them using the power of attrition and cohesion. Finally it has to form a barrier to the passage of water, air, dust and every kind of substance that could penetrate between the blocks, if not sealed adequately. In order to fulfil this function the mortar beds have to be quite subtle with a thickness of 5mm to 15mm by using square blocks for mural constructions (ministerial ordinance D.M. 20.11.1987).The same ordinance defines four types of mortar, beginning with the cement ones (type M1) up to the sand and lime one (type M4). The best mortars to be used for constructions with Fiorditufo are the mixed pozzolan mortar one (type M3) and the silicious sand one (type M2). Both are to be mixed with hydraulic lime which develops its noted pozzolan properties and maintains a very good level of processing and plasticity for a sufficient period of time and offer a resistance to external penetrating substances which is similar to that of the Fiorditufo blocks. The surface of the tuff is not plain. It is rough, bubbly and covered by broken crystals. Consequently it is chemically insature. For mural construction with tuff this means a very high level of adherence, if the tuff is cleaned and wetted well and if the mortar gets applied in thin stratums, so that it can penetrate and follow the irregular surface of the blocks. During the processing phase the liquid mortar adapts to the surface of the blocks.The weight of the mural constructions and the other structures accentuate the reciprocal contact between the mural components and increase the attrition so that the power of adherence between the blocks and the mortar gets perfect.During the casting of the floors their own weight pressing on the mural construction, together with the plasticity of the mortar beds of the load-bearing wall, realise a reciprocal adapting process of these two structures independently from the time needed for the hardening. This adapting process can go on also after the removal of eventual supports of the floors and the successive putting of permanent additional stratums. The adapting process between the floor panel and the upright mural construction, that gets realised by the mortar beds, leads to a light rotation of the upright panel. This panel balances itself in the right position to receive the support of the floor with a quite uniform distribution of the pressure. This phenomenon goes on until the mortar plasticity is still at work, either by putting successive weights upon the floors or by the weight of the mural constructions themselves and of the floors of superior order transmitted to the mural level under examination during the construction process.