In article ,
"Andrew Mawson" writes:

When I went to bricklaying classes years ago we always used dry lime /
sand mix as the mortar. It worked very well and in theory was knocked
down at the end of each session. In practise is was amazingly solid
even after only 4 hours of standing.

This is training mix. It behaves like mortar and even appears to set
as it dries out. However, it doesn't really set and is ground down
and rewetted for reuse. If you left it long enough, the lime would
actually set (turn to chalk), but not noticably in a week or so that
training projects exist before being demolished.

--
Andrew Gabriel