What you will notice
Crumbling walls wear down slowly, so it is easy to miss until a lot is gone. Look for:
Sand on the floor
A small pile of grit along the base of the wall.
Mortar you can scrape out
A key or screwdriver digs into the joint easily.
Deep, empty joints
The mortar has worn back far behind the face of the brick.
Flaking brick faces
Brick surfaces peel or pop off in thin layers.
Loose bricks or stones
A unit wiggles or has fallen out.
White, fuzzy powder
Salts left behind by water moving through the wall.
Damp, dark patches
Wet areas that stay after rain or melt.
Bulging or leaning sections
Part of the wall pushes out of line.