Cracks in a wall: when they are normal and when they are not

The most common case: fine plaster cracks

Thin, hairline cracks in plaster are usually just the building settling or materials expanding and contracting with the seasons. This is especially common in older wooden houses in areas like Kalamaja or Nõmme, where timber frames move slightly with humidity, and in panel buildings where plaster skims over concrete joints that shift a little as temperatures change.

These cracks are typically straight or slightly branching, no wider than a hair or a fine line, and they do not grow noticeably from one year to the next. They often appear near ceiling corners, above door frames, or along the line where two panels meet.

If that describes what you are looking at, the fix is straightforward: rake out the crack a little, fill it with a flexible filler, sand it back and repaint. It is a job many people manage themselves over a weekend, and it is also exactly the kind of small job our painting and decorating service handles, from 12 € per job.

Which cracks deserve a closer look

Some cracks are worth more attention before you reach for the filler. Diagonal cracks running from the corner of a window or door towards the ceiling or floor are a common warning sign, because they often follow the path of stress around an opening rather than simple surface shrinkage.

Also worth watching: cracks wider than about 3 millimetres, cracks that keep reappearing after being filled, cracks that run through the full thickness of a wall rather than just the plaster skim, and any crack that is visibly wider at one end than the other. A crack that has clearly grown since you first noticed it matters more than one that has stayed the same for years.

None of this means the building is in danger. It means the cause is worth identifying before you cover it up, particularly if the crack sits in or near a load-bearing wall. We do not carry out work on load-bearing walls ourselves, and any genuinely structural question should go to a structural engineer or the building's own documentation, not to a handyman with a tub of filler.

• Diagonal cracks from the corner of a window or door
• Cracks wider than roughly 3 mm
• Cracks that go through the full wall thickness, not just the surface
• A crack that is clearly wider now than when you first saw it
• Cracks that reopen soon after being filled
• Cracking paired with a door or window that has started sticking

Cracks in a plasterboard partition are a different matter

Plasterboard (drywall) partitions crack for their own reasons, usually unrelated to the building's structure. The most frequent cause is movement at the joints between boards, where the jointing tape and filler were not built up in enough layers, or where the frame behind the board was not properly braced.

Cracks along a straight seam, especially where two boards meet or where a partition joins the ceiling, are almost always this kind of joint failure rather than anything structural. Cracks near a corner where a door was cut into the partition are also common, because that is where the board flexes most.

This kind of cracking is repairable and, once fixed properly with fresh tape and several thin coats of filler, tends to stay fixed. If a partition has several recurring cracks, it is often worth having the joints redone properly rather than patching the same spot again. Our plasterboard work, from 28 € per job, covers exactly this kind of repair.

What to check yourself before deciding

Before calling anyone, a few minutes of checking will tell you a lot. Measure the crack's width at its widest point and mark the ends with a pencil and today's date, so you can see in a month or two whether it has moved.

Look at what is nearby: is the crack close to a window, door, or the corner of the building? Does it appear on both sides of the wall, inside and out, or only on one face? Is there any sign of dampness, discolouration or a musty smell around it, which would point to a moisture problem rather than pure settling.

Check whether doors or windows near the crack open and close normally. A door that has started binding at the same time cracks appeared is a stronger sign of movement in the frame or floor than a crack on its own.

When to call someone, and who

If the crack is thin, stable, and away from a load-bearing wall, it is a cosmetic job: fill, sand, paint, done. That is straightforward odd-job or painting work, and our hourly rate for odd jobs starts at 39 €, with a 25 € call-out in Tallinn that comes off the bill if the work goes ahead.

If the crack is widening, diagonal from an opening, running through the wall's full thickness, or paired with sticking doors and windows, stop filling it and get an assessment first. In an apartment building, the korteriühistu (apartment association) should also be told, since a structural issue can affect more than one flat.

For anything that turns out to touch a load-bearing wall, the next call is to a structural engineer or the relevant department at the city, not to us. We are glad to look at plaster and plasterboard, but we do not take on load-bearing wall work, and a guide that pretends otherwise would not be doing you any favours.