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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. badly drawn plan

  • Is the external brickwork in English/Flemish bond? Could your screwholes have accidentally been aligned between courses (i.e. through lime-plaster into lime-mortar and not into brick). Are your screwholes towards the top of the wooden mounting-board? A rough floor plan might help (I'm wondering how a larder could contain a fireplace) – RedGrittyBrick Jul 3 '15 at 13:56
  • @RedGrittyBrick I think it's Flemish bond. I wondered when I originally put it in whether I'd got between two courses of bricks, so went down one inch and to the right about three inches and it was still powdery. Thinking about it perhaps I just had bad luck and the first drill hole just it vertical mortar, and the subsequent holes (all precisely aligned with a spirit level) hit horizontal mortar. – abligh Jul 3 '15 at 14:26
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    I think I'd remove a small section of plaster in an area where subsequent repair will be hidden by the "coat thing". If the bricks are crumbling you may need to identify the cause (water running down a chimney?), rectify the cause and replace damaged bricks. If the bricks are OK and the screwholes all go into mortar I would just mark the brick centerline on adjacent wall for screwhole positioning and repair the plaster (using same sort of plaster). – RedGrittyBrick Jul 3 '15 at 14:43
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Here's what I did (probably a little over-engineered but it worked well)

  • Filled current holes and the surrounding mess
  • Got 135mm long, 7mm screws with wall plugs, and drilled 10mm holes for them
  • Located the holes 50mm above the current holes, 50mm being approximately half a course of bricks

Whilst drilling I think the problem might have been that I'd gone between two brick courses, but this was probably compounded by the fact the plaster was thicker than I thought (it might have been 60-70mm before it hit the brick by the noise of the drill), so the ridiculously long far too heavy duty screws probably did the trick.

Each of the screws is apparently rated to hold 90kg, though I doubt either the wall or the coat-hook thing itself would be anywhere near that.

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One trick is to undersize the holes required for the rawl plugs you use. E.g. if a 6mm bit is specified for the plugs, use a 4mm bit to drill the hole.

I've used this trick to work with older/crumbly plaster walls many times (both on brick and with wood lathe).

Note this is really just a workaround - RedGrittyBrick has the answer for a permanent fix to what could be the root cause of the powdery nature of your walls.

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