What a crumbling foundation looks like
Old stone and brick basements do not fail like poured concrete. They do not usually crack in one long line. They wear away joint by joint.
Sandy mortar
That turns to powder when you rub it
Small piles of sand
On the floor along the base of the wall
Gaps between stones
Deep enough to push a finger or a screwdriver into
Loose stones or bricks
That wiggle or have fallen out
Dark, wet joints
After rain or in spring
White crust
On the stone where water dried
A bulge
Where a section of the wall has pushed in
Crumbling brick faces
That flake off in layers
Look closely near the top of the wall, under windows, and below any outside downspout. Those spots get the most water.