I have a house in the UK built circa 1870. The external walls are London brick in Flemish bond I think, and are in a single layer (no cavity wall construction). At some point many tens of years ago, a larder was built alongside the house (so the previously external wall of the house forms the inside wall of the larder). Behind this wall is a fireplace and chimneys. Now it is an internal wall, it has about half an inch of plaster on it, which appears to be directly affixed in some way (as opposed to using plaster board - I think that's 'dry wall' in the US).
(I've simplified this slightly so you get the picture. It may be that the larder (in a slightly different form) was original. However, the wall is certainly load-bearing - it supports the external wall to all the floors above - and where internally you get to the larder there a huge internal lintel or joist.)
Some years ago I attempted to attach an old (much loved) thing for hanging coats to this inside wall. The thing for hanging coats is essentially a plank of wood, about 3/4" thick, 4" high, and 6 ft long, with a number of coat hooks along its length. It has 5 holes in it for mounting screws.
My strategy was simply to drill into the wall using a masonry bit and hammer drill, and mount the 'coat thing' flush against the wall with screws and wall plugs / rawl plugs. I used a 6.5mm drill bit, and screws about 3.5 inches long (so about 2.75 inches was in the wall when done). A brief amount of investigation showed the wall was powdery, even an inch or more, by which I mean that even going into the brick, rather than drilling a clean hole as one would normally expect, the brick appeared friable. I'd used the longest screws I felt prudent (what I don't want to do is go through the back of the chimney lining), though I may have been over conservative.
It sort of worked, but the coats are heavy, and every year it came out the wall another few millimeters, and finally fell off a few days ago. I now have the task of remounting it.
What's the best way to do this? Would longer screws actually help? What's the best way of working out the usable thickness of the wall? Why is the brick so friable in the first place? Is this likely to be result of the chimney behind?
I've added a badly drawn picture below.