Il trasporto di vapore d'acqua in pareti di blocchi forati - Water vapour transfer in hollow block walls

Current standards provide a method for calculating the hygrometric performance of a multilayered wall (UNI 10350) that adopts simplified hypotheses that do not take into account important aspects like the dynamics of capillary adsorption. The value of the global resistance to the transmission of vapour, to be used in the control, is currently assessed using the permeability value supplied by UNI 10351, regardless of the geometry of the block and the type of structural brick. Within the framework of the Progetto Finalizzato MSTA2 from CNR, Bari Polytechnic carried out a series of measurements of the permeability to steam of walls made of plastered hollow blocks. The test, conducted on four types of walls with normal structural bricks and light weight ones, demonstrated little sensitivity to the resistance to the diffusion of water vapour with a variation of the vapour pressure or its gradient. What emerged was the importance of the permeability to water vapour of the brick with respect to the permeability of the mortar used for the joints and for the plaster. The test results showed that the equivalent permeability values, commonly used in the hygro-thermal design of structural brick walls, are decidedly lower compared to those in use.