Fixing shelves: old stone walls versus new-development walls

What a pre-war stone wall is actually made of

Older buildings around the city centre, Kalamaja and similar districts often have load-bearing walls of limestone or brick, sometimes half a metre thick or more, finished with a layer of lime plaster that was applied by hand. That plaster is rarely flat: it can vary in thickness across a single wall, and it is softer and more crumbly than modern cement-based render.

Underneath the plaster you may hit solid stone, a brick joint, or an air gap where the plaster has come away from the masonry over the decades. This unevenness is the main reason drilling in these walls feels unpredictable: the same drill bit can go through soft material for two centimetres and then suddenly hit dense stone.

The wall itself is usually strong enough to hold real weight, once you get a fixing properly into the masonry rather than just into the plaster skin. The skill is in reaching that solid material without the hole wandering or the plaster crumbling round the edge.

What a new-development wall is made of

New-build flats in and around Tallinn are usually finished in one of two ways: internal partition walls in gypsum board (plasterboard) on a metal or timber frame, or load-bearing and dividing walls in aerated concrete blocks, sometimes called gas concrete. Both are far more uniform than old plaster, but neither behaves like solid brick or stone.

Gypsum board is thin, generally around 12 to 15 millimetres, with mostly hollow space behind it apart from the studs. A screw driven straight into the board with no proper plug will pull out under the weight of anything heavier than a picture frame.

Aerated concrete is a light, porous block that is easy to drill but also easy to crumble if the wrong plug is forced in. It holds fixings well when the right type is used, but ordinary wall plugs designed for brick tend to spin uselessly or crack the block.

Which plug goes in which wall

For solid stone or brick behind old plaster, a standard nylon wall plug with a metal screw works well once you drill through to the masonry, though for anything heavier than a light shelf a longer plug or a resin-set metal anchor gives a more secure hold in soft lime mortar joints.

For gypsum board, ordinary wall plugs are the wrong choice. Use a plasterboard-specific fixing: either a self-drilling cavity plug that grips as it turns, or, for real weight such as a loaded bookshelf, a spring or butterfly toggle that opens up behind the board. Where possible, locating and screwing into the timber or metal stud behind the board is stronger than any cavity fixing.

For aerated concrete, use a plug made specifically for this material, often labelled for gas concrete or aircrete. These are wider and coarser than standard plugs so they grip the soft block instead of spinning it loose. Ordinary brick plugs and standard screws are best avoided here altogether.

• Solid stone or brick under old plaster: nylon plug and screw, or a resin anchor for heavier loads
• Gypsum board with no stud behind it: spring or butterfly toggle for weight, self-drilling cavity plug for light items
• Gypsum board with a stud behind it: screw straight into the timber or metal stud
• Aerated concrete block: a plug made specifically for gas concrete, not a standard brick plug

How to tell the wall type before you drill

Tap the wall with a knuckle. A dull, solid sound with almost no give usually means stone, brick or concrete block behind the plaster. A hollow, drum-like sound means gypsum board with air behind it, though tapping near a stud will sound firmer than tapping between studs.

Drill a small test hole, around 5 millimetres, in an inconspicuous spot and watch the dust. Grey, gritty dust and a slow drill mean stone, brick or concrete. Soft white powder that comes away almost instantly means plasterboard. Aerated concrete gives a fine, pale, sandy dust and drills noticeably faster than brick.

Check how old the building is and what you already know about it. A pre-war stone building in Kalamaja or Nõmme is very unlikely to have gypsum partition walls in its original load-bearing structure, while a flat in a new development built in the last decade or two is very unlikely to have solid stone behind the plaster, apart from occasional structural columns.

What to do yourself and when to call a handyman

Hanging a light picture, a small shelf, or a mirror under a few kilograms is a reasonable job to do yourself in either wall type, provided you use the right plug for the material and take a little care over where you drill. A cordless drill, the correct bit, and fifteen minutes is usually all it takes.

Heavier shelving, wall-mounted units, large mirrors, or anything going into a wall you cannot confidently identify is where it becomes a false economy to guess. A wrongly chosen plug in stone can mean redrilling several times and enlarging the hole each time, and a wrongly chosen plug in gypsum board or aerated concrete can mean the fixing failing weeks later, sometimes taking a chunk of the wall with it.

We fix shelves and mirrors from 39 € per hour and handle general odd jobs from the same rate, and we come to homes across Tallinn and Harju county. For a straightforward job we usually give an estimate over the phone, and for anything unusual we are glad to look at a photo first.