The Natural Philosopher wrote:

Anything from 2:1 sand:cement to 5:1 or even 7:1 will hold bricks together.

Opinions are divided between the '2:1 will be imprevious, and therefore
won't suffer water penetration and frost cracking' (but the bricks may)
to 'i'll use something with lime that is so soft that it won't crack
even if water does get in'

Mixes stronger than 3:1 shrink during cure and microcrack extensively.
This makes them porous and prone to frost damage. The numerous
microcracks undo the advantage of the stiffer mix.

3:1 is extra strong for apps where the mix can shrink without
cracking, but bonded to bricks isnt one of those. 3:1 performs beter
than 2:1 with brickwork.


I ended up with a sort of 6:2:1 mix of sand:white portland:hydrated lime
for a visually pleasant mortar.

The old 9:2:1 mix fails routinely, as do many other cement/lime mixes.
AFAIK 1:1:6 is the only cement:lime proportion that has been found to
be ok. Cement and lime are uneasy bedfellows.

For the sake of completeness I suppose one could mention clay mortar,
or even the old lime mud and straw recipes.


NT