If you go to your local builders' merchants and ask for a bag of lime you
will not get quicklime, calcium oxide, since it is caustic stuff. You will
get hydrated, non-hydraulic lime; I know this because I have a bag of it.
Hydrated = slaked. Non-hydraulic means it will not set underwater.
I have no doubt quicklime can be obtained, but who wants to handle
such stuff, with all the dangers involved, when you would have to
hydrate/slake it yourself anyway. In olden days, limestone/chalk would be
fired to drive off the carbon dioxide, giving quicklime, calcium oxide; this
would then be slaked with water to give slaked/hydrated lime. Quicklime is
no good for building, it is an intermediate step. Lime mortar uses
hydrated/slaked lime with sand, in a 1:3 by volume mix. It takes weeks to go
off, and sets by reaction with co2 in the atmosphere, essentially turning
into limestone.
Hydrated building lime is essentially the same stuff that goes on your
garden.

Andy