Dried material layer migration

The two-zone model described above allows for the multiple mechanisms. The rules that govern these mass transfer operations are completely analogous to those governing heat transfer already discussed. The migration of vapor through the dried material layer can be expressed as... 

All materials are polarizable, but vacuum is not (although it can hardly be called a material). With only bound charges, an electric field can only displace charges so that dipoles are formed and the material is polarized. If the hiomaterial is dry, double layers (Section 7.5) will not be formed. A dry hiomaterial in contact with dry electrode metal forms an interface. With free charges, there are important additional effects from the migration of these in an electric field. 

The present authors are of the opinion that the use of geosynthetic clay liners (a thin layer of dry clay powder sandwiched between two geotextiles) as gas-resistant membranes below buildings is not acceptable. This is because the liner relies on the bentonite material becoming wet to form a barrier and this cannot be guaranteed. Even if it is pre-wetted the clay can dry out and crack, which will allow gas to migrate through it. 

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