[Cob] lime for exterior cob wall in northern california - what type of lime to get, and where to buy?

[Prentice Fish]

Hello everyone,

Recently I've built a 120 sq ft cob building in northenr California, USA,
and enjoyed that experience. The cob walls start out on a rubble foundation
at about 12 inches thick, and taper down to about 8 inches thick at the
roof line. The roof of course overhangs the walls quite a bit, for some
protection against driving rains. I did have the good fortune of having a
tractor to mix the cob, and lift it to the building site.  Even so, it was
a lot of work, doing it by myself.

In a few months I'd like to plaster a layer of subsoil/clay, with lime
added, on the outside of the cob, for some protection against driving
rains.  But I'm not seeing any good lime available here in northern
California.

My questions are: what type of lime should I buy, and where can I buy it in
northern california?

I've been to one local hardware store - Home Depot - and it has "Type S"
lime.  I think this is not what I want, but I don't know. I called one
local masonry store, and could tell they knew even less than I, which means
they knew next to nothing. Thank you for any thoughts/suggestions!