An uneven wall before wallpapering: how to smooth it out

What the bumps and waves actually mean

A wall rarely gets uneven by accident. In older buildings the surface has usually been repaired more than once, and each layer of filler, paint and old wallpaper paste adds its own texture. When you strip wallpaper back to bare wall, you are often looking at the accumulated history of several previous jobs rather than one single problem.

In panel buildings, waviness is frequently built into the concrete panel itself, a shallow dish or ridge left from the original casting that no one bothered to correct because wallpaper hid it. In 1930s wooden houses the plaster is often original lime plaster on timber lath, and small cracks, bulges or soft patches are a sign the plaster has moved slightly over the decades, which is normal rather than alarming.

None of this is structural and none of it is dangerous. It becomes a problem only at the point you want a smooth, even finish, and light or glossy wallpaper will show every one of these irregularities as a shadow or a highlight once it is up.

How to check how big the problem really is

The simplest test is a straight edge. Hold a spirit level or a length of straight timber, at least a metre long, flat against the wall in several directions, horizontal, vertical and diagonal, and look at the gaps that appear underneath it against the light.

A torch held at a low angle across the wall, almost grazing the surface, will throw shadows into any dip and highlight any bump far more clearly than normal room light. This is worth doing before you decide anything, because a wall that looks fine under a ceiling light can look quite different under raking light, which is closer to how wallpaper will actually be lit once it is on the wall.

Note where the gaps are and roughly how deep they are. A few millimetres here and there over a small area is a very different job from a wave that runs the length of the wall or a dip you can slide a finger into.

When sanding and filling is enough

If the straight-edge test shows gaps of a millimetre or two, and the wall is otherwise sound with no soft or crumbling patches, ordinary filler and sanding will usually get you a good enough surface. Use a ready-mixed or powder filler suited to interior walls, apply it with a wide filling knife in thin layers, and let each layer dry fully before the next.

Sand between coats with fine abrasive paper, roughly 150 to 180 grit, and check progress with the torch again rather than by eye alone under normal light. It typically takes two to three thin coats to get old patch repairs level with the surrounding wall, since a single thick pass tends to shrink and crack as it dries.

This is realistic work for a careful DIYer with a weekend to spare, and it is the more economical route when the wall's problems are cosmetic and localised rather than widespread.

When a full skim coat is needed

A skim coat, a thin, continuous layer of plaster or fine finishing compound applied across the whole wall, is worth doing when the unevenness is widespread rather than confined to a few patches, when the straight edge shows waves of several millimetres or more, or when the existing surface has multiple old repairs of different materials that will never quite match under filler alone.

It is also the right call if you plan to hang light-coloured, plain or glossy wallpaper, since these show far more of what is underneath than a patterned or textured one. Trying to fill and sand your way to that standard across a whole wall usually takes longer, and costs more in materials and time, than having it skimmed properly in the first place.

Skimming is a skilled trade in its own right: getting a flat, even finish across a full wall with a trowel takes practice, and a poor attempt can leave trowel marks that are just as visible as the original problem. This is one of the jobs covered by our plasterboard and wall finishing work, priced from 28 € per job, and it is often more cost-effective than repeated rounds of DIY filling that do not quite solve it.

How your choice of wallpaper affects the outcome

Wallpaper is not neutral about wall condition, and this is worth deciding before you buy rolls rather than after. Plain, light-coloured or glossy wallpaper reflects light evenly across its surface, so any dip or bump underneath breaks that reflection and becomes visible as a shadow line, sometimes worse than it was on the bare wall.

A heavier textured wallpaper, such as one with an embossed pattern, a woodchip-style finish, or a deep repeating relief, behaves very differently. Its own surface texture breaks up the light in a way that hides minor waviness and small filler patches, which is exactly why textured papers have stayed popular in older Estonian flats where walls are rarely perfectly flat.

If your wall check in the earlier steps showed only minor, scattered flaws, choosing a heavier textured paper can be a legitimate and cheaper alternative to a full skim coat. If the walls are badly wavy, no wallpaper texture will fully disguise it, and the prep work needs to happen regardless of what goes on top.

• Check the wall with a straight edge and raking torch light before choosing wallpaper
• Minor, scattered flaws: filler and sanding, then almost any wallpaper will do
• Widespread waviness or multiple old repairs: a skim coat first
• Plain, light or glossy wallpaper: needs the flattest wall you can get
• Heavy textured or embossed wallpaper: forgives minor unevenness
• When in doubt, test with a torch again after filling, before you commit to paper

How much time and money this takes

Filling and sanding a wall with a few patched areas is generally a one- to two-day job including drying time between coats, and materials cost relatively little. It is realistic to do yourself if you have the patience for the sanding and are prepared to check your work with a torch rather than trust your eye in flat light.

A full skim coat across a room takes longer, since the plaster needs time to set and be finished properly, and it is not a job to rush if you want a genuinely flat result. Doing it as a fixed-price job means you know the final figure before work starts rather than paying by the hour for something that is hard to estimate from the outside.

Once the wall is ready, hanging the wallpaper itself is a separate stage, and our wallpapering service starts from 10 € per job for straightforward rooms, with the price depending on the size of the wall and the paper chosen. Call-out within Tallinn is 25 €, deducted from the bill if the work goes ahead, and any fixed quote for a larger job is valid for 30 days.