People tend to find foundation cracks by accident. You move a rug, pull a bookshelf away from the wall, or stand in the driveway one evening when low sun catches the brick at an angle. Then the question is what to do about it.
Reading the crack
Hairline cracks running roughly straight across a garage floor or patio are usually concrete shrinkage. Lots of them show up within a few years of a pour and then stop.
Others are more telling. Brick that breaks in a stair-step pattern along the mortar joints. A diagonal crack running up from the corner of a door or window. A crack that’s wider at the top than at the bottom, or where one side has shifted up or out from the other. Those patterns suggest part of the house has moved relative to the rest.
The easiest test costs nothing. Put a small pencil mark at each end of the crack and write the date next to it. Check again in a month or two. If it has run past your marks, it’s still moving.
Repair options
For a stable crack, sealing is usually enough: epoxy or polyurethane injection in concrete, repointing in brick, tape and mud in drywall. Ask the company which material they’re using and why.
For a crack caused by movement, the order matters. First the cause gets addressed, usually with slab foundation repair or drainage changes. Then the cracks get sealed and patched, once the house has stopped moving. Patching first and supporting later means doing the patch twice.