We recently did some repointing on the outside wall of our 18th-century brick home. While resetting some loose bricks, we found a hollow space on an inner layer of brick--the wall seems to be three bricks strong--where there was no brick left, just a heap of fine brick powder.
How would we best go about diagnosing the structural integrity of the walls, now that this finding has brought up the possibility that there may be other powdered bricks present? Other than in the attic, none of the brick walls are exposed in the house interior; they're all covered up either with drywall or with lath and plaster. Does all of it have to come off for a visual inspection, or are there other methods?