[Cob] Ivy on cob walls

[Scott Race]

  I was trying to think of alternate ways to protect cob walls from the
elements.
Can anyone think of any possible problems if you lime rendered your walls
and then let ivy grow all the way up?
   I would think the ivy would keep potential rain from touching the cob,
thus it would never really get wet, and if it did, the lime render would
protect it.  Just another layer of protection and would probably look cool
with a living roof.

Scott