mortar takes a month to get its full strength up. 5:1 is more than
strong enough. I take it youre using all new bricks, not salvo old
ones. If youre using old you need a different mortar altogether.

You are right I am using new engineering bricks but planning to use
older common bricks above them...thinking of using a 6:1 mix for them.

... A lot of 19th century houses wrere
built with sod all in the way of foundations.

You mean there are no foundations?

So is there a damp problem or not? I'm not clear. The bricks in the
soil will of course be damp, but this wont normally transfer itself to
the living area. Think more explaantion is needed.

No there isn't a damp problem; I've simply assumed that laying new
bricks on top of slightly damp ones would required some waterproofer or
a new DPC. I've opted for waterproof mortar and a few rows of
engineering bricks.

Thanks for your help,

Alex