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I have a niche/nook in a room (marked red)

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and some leftover chipboards of width 16mm. Together they should make a simple shelf. So I would cut the chipboards to the same width/depth as the niche/nook (minus some mm) and for each board

  • drill 4 holes to the opposing sides (marked blue) at a certain height
  • put rawplugs/screw anchors and screws in the holes
  • put the board on top of the 4 screws.

The wall is made of concrete (right side) and bricks (left side).

Questions:

  • What types of screws should I use (thickness, material) so that a board can carry up to 10kg? The weight will not be concentrated on one spot, it will be distributed quite evenly. E.g. one board should carry a basket (almost same size as board widht/depth) which will be filled with empty glasses and bottles.
  • What options do I have to compensate inaccuracy of the drilled holes? I never manage to make all holes on the exact same height, or to make all of them perfectly horizontal!
  • Using a level should fix the "not at the exact same height" issue - or at least get you close enough that a very thin shim of fabric or felt will level your shelf. What is the purpose of the dowels and screws? Are you screwing the dowels into the walls? Could you just push the dowel into your newly drilled hole and let it stick out into space, allowing the shelf to rest directly on the dowel? – FreeMan Feb 3 at 20:56
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    Why not use the screws to fasten wedges or brackets to the wall? That way the screw is in tension (where it's strong) instead of shear (where it's weak). I would use wedges, that way you can compensate for any positioning errors by drilling the hole in the wedge in a different place to suit. – Harper - Reinstate Monica Feb 3 at 20:58
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    I think that "dowels" in this context must be referring to those plastic inserts for concrete walls or hollow walls. Also, this looks like more of a "nook" than a corner if it has a wall on both sides, but that's just a translation issue. – JPhi1618 Feb 3 at 20:58
  • I corrected the question (replaced the word "dowel" by "rawplug"/"screw anchor" and "corner" by "nook"/"niche"). They were translation errors. – Kjara Feb 7 at 8:10
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Almost any good quality 5mm (#12) screw in a set of four will carry 10kg (~22 lbs.) without issue, assuming that you're in solid anchoring. Plastic plugs of the correct size should do well, or wood if you're precise.

I would actually consider using stainless steel machine-thread screws with hex heads. They'll look nicer and allow you to rotate the head to get some degree of adjustment with respect to out-of-level conditions. You could also slip smooth bushings over the protruding portion of the threads to clean up the appearance, and you could place small silicone bumpers on the top surface to reduce rattle and/or make additional height adjustments.

Run the screws in at least 30mm (~1-1/4") and only leave them extending about 20mm (~3/4"), to reduce torque load.

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To increase precision when drilling, level accurately and start with a small drill bit. Select a location that's not troublesome, such as at the center of a brick.

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I would use 3/16 Tapcon screws. (Use 5/32 masonry bit.) The Tapcon screws are thread hardened specifically for use in masonry materials. The hardened thread will hold up better than a wood or machine screw. A lighter (smaller diameter) screw will likely suffice, but in my experience sometimes heavier weights get placed on shelves.

To level the shelves, I would apply felt adhesive pads, like those used to prevent furniture from marring surfaces, on the bottom of your shelves. They are compliant, and faced with the head of the Tapcon screw, they will deform. That will help keep the shelf from sliding, and moving. If the shelf is not even on the screws, you can multilayer the pads to get things approximately right.

For drilling level, you can use a level, but a laser level, if you have one available, is an easy way to get a level line projected on to the wall. You may also wish to apply painter's tape to the wall and premark your desired holes on the tape. If you can, avoid putting the screws into grout, and stick to the brick area, as it is more rigid, and less likely to crumble over time.

If you mess up with the Tapcon, there are soft plastic inserts. Either re-bore to a larger size, or put the inserts in, and use a smaller hardened screw like the Tapcon.

You are perceptive to know that masonry screws are not precisely located sometimes. If you end up with a screw that is real high, you can use a spade bit or if you have them, a Forstener bit, both nearly flat bottomed, to lightly hog out shelf material to make a better fit for a level shelf. Still use the felt pad(s) to have a compliant resting spot on the screw.

A hammer drill is much better than a regular drill. Should you have a friend who offers you a rotary hammer drill, be nice to them and get the appropriate size bit from him. The rotary hammer is the best tool for boring into these materials, and is not only faster, but will place far less wear and tear on the bit.

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