In article ,
The Natural Philosopher writes:
Using a lot of cement fills up the holes between the sand completely,
making the mortar impervious, but according to another poster, it may
crack on setting, nullifying the benefits. Never seen it myself even in
lumps of 100% cement.

Some previous occupant of my house repointed a couple of areas,
very small fortunately, with 100% cement. It resulted in a neat
crack line all the way along, and was impossible to remove without
damaging the brick faces. You probably wouldn't notice shrinkage
in a lump, but force it into a gap and let it set, and you'll notice
it shrinks lots.

For brickwork, you want a mortar that is flwable enough to tamp bricks
down ion accurately, and stays soft long enough to get a decent line
laid, and yet is solid enough not to splump when you lay the next course
over it. and is relatively tough and water resistant.

A lot depends on the bricks too - porous commons will suck the mortar dy
unless soaked first, and cause it to go fairly solid fairly quickly.
Thats someimes useful, as it stabilises the course ready for the next one.

I'd say about 4:1 to 6:1 builders sand to cement makes a decent mix, and
you can add lime and subtract cement.

Some cement:lime ratios are particularly bad though, with
the cement failing to add strength and preventing the lime's
healing properties from working. 1:1 is safe from this though.

You also need to know if the wall is intended to be one solid item,
or if it's designed to move around. Cement mortar is fine for a
solid wall, but lime mortar walls are not intended to be solid,
and mixing areas of 'solid' cement mortar in to one can cause bad
damage to the wall as a whole.

--
Andrew Gabriel