Repairing Cracked Plaster in a Period London Home: Movement, Filling, and When to Reskim

Cracked plaster is a common starting point for redecoration work in period London homes. The decision that matters first is not which filler to buy — it is whether the crack is a stable surface fault you can fill and paint over, or a sign that the wall or ceiling behind the finish needs attention. This guide sets out how we read cracks, how filling is done so it lasts, and where the honest answer is a reskim rather than another round of patching.

What decides the repair route

Three things decide it: whether the crack is stable, how much of the wall is affected, and what finish goes on top. A single hairline crack in an otherwise sound wall is a filling job. A wall with widespread fine cracking, areas that sound hollow when tapped, or cracks that have reopened after previous repairs is a different specification — and if the plan is wallpaper or a sheen finish, the tolerance for imperfection drops further. The finish you intend to use should be part of the repair decision, not an afterthought.

Reading the cracks before filling anything

Spend time with the cracks before opening a tub of filler. What you are checking for is stability.

• Hairline cracks that follow a straight line, often along joints or the edges of old patches, usually point to shrinkage or previous repairs rather than anything active.
• Wider cracks, cracks that are wider at one end than the other, or cracks that travel across both wall and ceiling deserve a closer look before any cosmetic work is done.
• Tap gently along the wall. Areas that sound hollow or "drummy" suggest the plaster has lost contact with the background, and filling the surface will not fix what is behind it.
• If a crack has been filled before and has reopened, either the movement has not settled or the previous repair was done on an unsound base.

None of this replaces looking at the cause. If cracks are wide, keep changing, or sit alongside sticking doors or sloping floors, have the movement assessed before spending on decoration. Filling a crack that is still moving is work you will simply repeat.

Filling stable cracks so the repair lasts

For hairline and stable cracks, the workflow matters more than the brand of filler.

1. Open the crack slightly with a scraper or blade to remove loose, dusty material. Filler bonded to dust fails.
2. Brush or vacuum the crack clean. On deeper cracks, dampen or prime the inside according to the filler's instructions so the background does not pull moisture from the mix.
3. Press the filler in with a blade, working it into the crack rather than skimming over the top. For fine cracks that may move slightly, a flexible filler is generally the better choice over a rigid one.
4. Overfill slightly. Most fillers shrink a little as they cure; a second thin pass after the first has dried gives a flush finish.
5. Sand flush with the wall, not just smooth — a patch that is smooth but proud shows up under paint as a shadow.
6. Check with a raking light held close to the wall before priming. The low daylight in many period London rooms hides proud edges until the paint goes on.

When filling stops being the answer

Filling has a natural limit. A reskim becomes the better route when:

• Fine cracks cover large areas of the wall or ceiling rather than a few defined lines.
• The plaster sounds hollow across meaningful sections — the surface may look intact but has detached behind.
• Previous patching has left the wall textured: hard patches, sanding dips, and edges that telegraph through paint.
• The next finish is unforgiving. Wallpaper seams follow every ridge, and sheen paints reveal patched texture that a flat matte would disguise.
• A ceiling shows any sagging or bowing between joists. Ceilings are the one area where "keep an eye on it" is not a plan.

In these cases, chasing cracks one by one produces a wall that is part old, part new, and never quite flat. A reskim gives one continuous surface with one suction level, which is what makes the final finish read evenly under light.

Matching the repair to the next finish

The repair standard depends on the finish. If the wall will take a flat or low-sheen emulsion, small filled cracks can be acceptable — matte finishes are forgiving. If the plan is wallpaper hanging, the wall needs to be flat, sound, and evenly absorbent, because lining paper and seams will trace every imperfection. If you are considering limewash as the finish, the substrate conversation happens first: limewash behaves differently over patched and sealed areas, so the repair and the finish need to be planned together. Our painting and decorating service covers the full sequence from repair through to the final coats.

The order of work once the route is chosen

Whether the job is filling three cracks or reskimming a room, the sequence stays the same:

1. Protect floors, joinery, and fittings.
2. Stabilise: rake out, clean, and treat cracks, and remove any loose plaster.
3. Repair: fill in passes, or skim the full surface.
4. Sand, dust down, and seal patched areas so they absorb paint at the same rate as the surrounding wall.
5. Apply the finish system — primer or base coats, then the final coats or paper.

Sealing patched areas is the step most often skipped. A raw filler patch draws paint in faster than the surrounding plaster and shows as a dull patch, known as flashing, under the finished coat.

Checklist before painting over repaired plaster

• Every crack has been opened, cleaned, and filled — not just skimmed over.
• Filler sits flush under a raking light, with no proud edges or sanding dips.
• Patched areas are sealed so suction matches the rest of the wall.
• The wall is dust-free before the first coat.
• Any crack suspected of movement has been monitored or assessed, not simply filled.
• For wallpaper or sheen finishes, the wall has been checked flat across the full surface, not just at the repair points.

Deciding with help

If your period home has walls that keep cracking and you want a straight answer on filling versus reskimming before any paint goes on, get in touch with Pulse N' Paint. We look at surfaces as part of period-property decorating across Central London, West London, South West London, and Surrey, and we will tell you plainly which route the wall needs.