Wall and decoration
Pathology of humidity. Coated walls in the building sector

To determine the diffusion resistance R_D of a paint film, or more generally of a waterproofing system, we need to know the system's intrinsic permeance: (π /e )_s (in g/m² · h · mmHg).

In fact, both official test reports and technical documents supplied by manufacturers express the permeance of the test specimen coated with the system: (π /e )_r in g/m² · 24 h.

This can be explained as follows: on the one hand, steam flow measurements are carried out over a 24-hour period (low mass loss of the wet cup); on the other, the pressure gradient is a function of the temperatures at which the tests are carried out (in compliance with the standard applied).