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I'm putting up heavy-duty book shelves up in a very long alcove. My problem is that I've discovered it's a dab and dot (dry lining) plasterboard that covers up old brick, which I've never installed on before. This type of plaster doesn't have studs.

So, the plan is to have a 10cm deep plug, going through the plaster into the brick behind.

I've made a plan below. Any comments on whether people think this will work?

  • Wall fixing: COREFIX METAL & PLASTIC 100 HEAVY DUTY DOT & DAB WALL FIXINGS 10 X 95MM 24 PACK. These have good reviews and seem to be made especially for this situation. Load-bearing advertised as 100kg for two brackets.
  • Shelves: Pine wood, 220cm (7.2ft) long, 23 cm (9") deep, 3.5cm (1.3") thick.
  • Brackets: Heavy-duty solid steel brackets (0.75kg=1.6 lbs each)
  • Load: Depending on the bigger/smaller books I put on the shelves, I've calculated the total load (incl the shelf) per shelf will be between 100kg to 140kg (220-308 pounds).
  • Positioning: I'm thinking three brackets: one in the middle, and two 20cm from the wall (see sketch). I've used the Sagulator and in terms of sag that should be fine.
  • Five shelves.

My worries are:

  • when I started drilling the holes for the brackets, the brick behind is very varied (it's an external wall in a Victorian house). So, sometimes I think I'll have to shorten the plug a bit because it's so hard I can't drill right to the end.
  • is my thinking right about the brackets? If two can support 100kg, three should go up to 150kg right? Or do I need four?
  • I can distribute books so that it's more like 100kg per shelf if needed.
  • is it too much stress on the wall?

So, should I go ahead, or do you recommend changing the plan in some way?

Plan for the shelves

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    This situation absolutely screams for floor-supported bookshelves.
    – Ecnerwal
    Commented Apr 14, 2023 at 12:19
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    Expecting/trusting plaster/drywall alone, to hold that much weight leads to sadness. Use the floor for weight support and maybe use the anchors to prevent the bookshelves from tipping over, but I would use the bricks.
    – crip659
    Commented Apr 14, 2023 at 12:46
  • I started writing, but there are too many variables here to give you a good answer in short form, including your technique. This calls for on-site intuition based on appearance, feel, and testing. Calculators aren't of much value. Maybe find a local friend who has lots of building experience to work-for-beer. Otherwise, follow the try-and-tug method. Don't walk away from a loaded shelf until you're convinced it'll stay loaded.
    – isherwood
    Commented Apr 14, 2023 at 12:57
  • Floor-supported shelves would be good but there’s cabinets underneath & cost to consider... I’ll go with the answer below but thanks for the tips!
    – MarkO
    Commented Apr 15, 2023 at 14:41

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Some thoughts…

"so hard I can't drill right to the end." Find out why. Victorian brick varies in consistency from 'dry sand' to 'bell-metal' for no apparent reason. An SDS ought to march through it though. If it can't, you've hit something 'other'. It might just be a pebble, but take steps to find out what.
If you're trying to do this with a domestic 'hammer drill', think again.
If you do find a particularly sandy one, pump it full of thinned PVA & wait 24h. Push some No More Nails ahead of the Corefix & leave another 24h before testing it for strength… & always test things for strength in a Victorian house. No two substrates are ever the same.

Corefix are fine for the task, but I'd always go for longer than you think, rather than shorter. Vertical capability is the same, but you're just grabbing more brick, to cover for the above variation in hardness. Go for the 120s.

If you're thinking of 150KG per shelf, it wouldn't hurt to drill an extra hole in the brackets & go three per support.

For sag, I'd pull the end brackets in a bit. For perfect balance 1/4, 1/2, 3/4 but that will be odd visually, so widen somewhere between balance & optics. By the time it's full of books, you won't really see it anyway.

As to the load bearing capability of the wall itself… I've never found the maximum. It seems to do just fine holding up a couple of books… & the next two storeys. Corefixes mean you don't have to take the plasterboard into account, you're in brick. Both my living room alcoves are full of books from waist-height to ceiling, using those cheap 70s aluminium supports you just fasten in a straight vertical line then clip shelf supports into. There are only two verticals per alcove. Shelves I think are old floorboards. I inherited them with the house 30-odd years ago & they haven't moved since. Alcoves are shorter than yours, maybe 180 each. One also has an entire TV/HiFi shelf hung off it too.

One rule of thumb I've always worked to is, "If you can measure it, do so. Once you're beyond that & have to guess, guess heavily on the side of over-engineering."

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    That’s a great answer, thanks! Sounds like I’ll have to borrow an SD drill. The bricks do feel extremely different behind it, but good to know how to deal with the sandy ones. Fingers crossed!
    – MarkO
    Commented Apr 15, 2023 at 14:38
  • The thing about 'diy drills' in victorian brickwork is you think you're drilling a 6mm hole, but by the time you've finished struggling, slipping, halting, clearing dust every inch, pressing with all your strength & generally bouncing round the hole for 5 mins, you end up with either a cone-shaped pit or an 8mm hole, which the plug wont bite into properly. If you drill with an SDS, not only will you nearly have to hold yourself back from falling through with it [always use the length stop so you don't go too far] but you'll have all the holes done in 5 minutes, and they'll all be actually 6mm.
    – Tetsujin
    Commented Apr 16, 2023 at 9:19
  • That describes my experience with diy drill exactly and also explains why the brackets came out of the holes I have already done on another part of the wall. 😩 but I’ll hopefully do it properly with the SDS drill next week!
    – MarkO
    Commented Apr 17, 2023 at 10:53

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