ISO 22185-1:2021 pdf download – Diagnosing moisture damage in buildings and implementing countermeasures — Part 1: Principles, nomenclature and moisture transport mechanisms.
4 Moisture transport mechanism To make moisture planning meaningful, the critical moisture levels shall be well defined. However, these boundaries are always more or less uncertain. The solution may be to introduce some degree of safety margin. The size of the safety margin that should be introduced depends on the severity of the impact of a moisture state above the critical one. In cases where the degradation rate can be controlled, it is sometimes even possible to allow moisture levels above the critical, if this does not affect the indoor climate, health or the expected lifespan of the material or the structure. Moisture in building porous materials transfers as vapour or liquid. Vapour transfers as diffusion and effusion caused by vapour pressure gradients, and as the diffusion caused by temperature gradient. Liquid transfers as capillary flow caused by the gravity in capillary suction. For vertical direction, liquid transfers also by gravitation. In the presence of gradient in total air pressure, liquid and vapour transfer due to the gradient in total air pressure in addition to the mechanisms described above. This is classified as a transfer by convection. Wind pressure and difference in air pressure caused by difference between indoor and outdoor air temperatures are typical examples that cause convective transfer of vapour and liquid through cracks in or between building materials and also through permeable porous material. Mechanical ventilation will also influence the gradient in total air pressure.
7 Phenomena resulting from moisture 7.1 Algae/bryophyte “Algae” is the generic term for a living being that performs photosynthesis on the earth other than bryophyte, fern plants, and seed plants, and includes blue algae (cyanobacteria) and green algae, etc. Bryophyte includes moss, liverwort and hornwort. When the materials are placed under the outside weather conditions, moisture content on the surface or the water droplets adhere to the surface may breed algae or bryophyte and may cause aesthetic problems. If the humid conditions are prolonged, it is more likely that algae and bryophyte are observed. Related terms: condensation, high humidity. 7.2 Aesthetic changes Wetting of a material that results in changes to pigments or accelerates other processes that result in staining or discolouration. Related terms: wetting, condensation, colour fading, stain. 7.3 Condensation Condensation is the change of the physical state of water from gas phase into liquid phase. Condensation occurs on a surface that is at or below the ‘dew point’ temperature. Related terms: wetting, high humidity. 7.4 Corrosion Corrosion means that a metal is altered or is consumed from the surface due to the rust by oxidization, or electrolytically by the differences of ionization tendencies. In some metals, when it rusts on the surface, it works as a protective film, and it does not spread any further.