This explains tooled stucco details and work like beaded
joints in stone work. The mortar was firm
shows how lime starts the initial set of cement
mortar, and delays the final set.
Mortar is not firm enough to rod off or work
with until it starts to set.
For example, a finish coat of stucco
is to be rubbed with a rubber float
when it starts to set up. Without
lime to add an early firmness to the
mortar, one would have to wait a long
time for the finish to start to set, and
not have enough time to float their wall
Lime is used in cement mortar for bricks, stones
enough to shape, yet there was time to shape the mortar.
An example of this is an apple pie. When the pie comes
out of the oven, it is too gooey to slice.
Once the pie cools, a neat slice can be made.
Three parts sand is too much, however.
this bag of Portland cement say 1/4th part lime.
A 50 pound bag of lime has about the
same volume as a 94 pound bag of
Portland, so it is about the same as
my 1/4 bag of lime to a bag of Portland.
The point is, the manufacturer,
Sakrete, wants their product to perform well,
and adding lime is important to them or they
wouldn't print it on the bag.
As a warning, lime also weakens the mortar and causes
shrinkage cracks. Much more than
1/4 of a bag can do more harm than good.