Background - our house was built in the 30s, has a square
footprint around 8x8m, and has no foundations to speak of. It's
made of stone + lime mortar, and the walls are between 50 and
60cm thick.

When we bought it 2 years ago, we noticed that the back wall had
at some point in the past bowed, so that while it's still
attached to the outer walls, it's come away from the internal
partition walls, causing a lot of cracks between the end wall
and the partitions, and the end wall and the ground floor ceilings.

We filled these cracks so that we may study future movement. Two
years on, the wall seems to have shifted by another mm or so.

The wall isn't sinking - there are no cracks at floor level
downstairs. The cracks appear about 1m above floor level, and
increase in size as you go upwards.

Similarly, the wall is still firmly attached to the two exterior
side walls. So it's only moving outwards in the middle. It's bowing.

I know the traditional fix for this is to tie the two opposing
walls together with steel tie rods, and spread the load on the
outside of the walls using steel plates.

I am considering doing this to our house. The obvious place to
run the steel rods is between the floor and ceiling. This would
be fine, since they'd run parallel to the joists.

Has anyone done this before, and do you have any advice to
offer? Is there anywhere when I could read up on this? Basic
stuff - like how big the rods should be, how big the plates
should be, how far apart, how many (two seems very common), that
kind of thing.

TIA

--
Grunff