Cob: mositure

[Darel Henman]

To back up the Shannon's statement that:

> .......... cob is that the material breathes, if you seal
> the exterior of the wall with something, the moisture will condense
> near the outside of the wall behind the sealant (cement, paint, etc.) and either
>    1 - Cause the cob to soften and/or separate from the sealant.
>    2 - Freeze and expand causing the exterior surface of the cob and
>        coating to break apart.
>    3 - Both of the above.
>

The use of hard cement over a cob or lime rendered walls in the U.K. as
well as the case you mention in Mexico, has shown the same results,
i.e., that cementing over a soil or lime based wall, will cause spalling
and other undesirable failures to occur.  This has been documented and
has shown up in restoration work on many historical buildings.

> 
> While I would tend to agree with the general sentiment (venting
> requirements vary from place to place), it is definitely not as simple as
> North and South.

No, there are various micro-climates.  The north and south was just a
rough mentioned to indicate that differences need to be considered.

Darel