Cob: outdoor plaster

[Scott Gregorie Howard]

I have a question about the best way to completely waterproof outdoor
cob. I have built an outdoor bench that will not have a covering.
Also, it is near to a garden beds and so cannot drain and leech any sort
of toxic chemicals.  

What is the best way to waterproof my bench? Lime plaster?

I own the cobber's companion, and know of several techniques, but I have
no experience in plastering and no experience in finding the proper
materials to make a lime-sand plaster for example.


Thank you,

Scott Howard

Whitman College Organic Gardening club