[Cob] Oils for finishing cob/plaster/wood

[Carrie J Horne]

> Can anyone comment on why linseed oil is always touted as the best for 
> finishing earthen floors etc.?  I know it's used for wood too...
> Is it cost, availability, suitability, etc....?
> Cheers
> Rodger

In The Natural Plaster Book by Guelberth and Chiras they say that, with
reference to plastered walls,  "various oils can be added to earthen
plaster to enhance its water resistance and durability.  Linseed oil is
one of the best...When exposed to oxygen in air as the plaster dries,
linseed oil becomes oxidized, and is then 'fixed' in the wall.  It also
increases the flexibility of a finish plaster allowing it to expand and
contract more than untreated plaster, which helps to reduce cracking. 
Linseed oil does all this while continuing to allow the wall to
breathe....

"A variety of other oils can be added as well, including canola oil, hemp
oil, and flax seed oil.  However, these have less body than linseed
oil--that is, they are less viscous (thick).  The more viscous linseed
oil also adds pliability, which other oils don't."

HTH,
Carrie