The short answer
New plaster usually cracks for one of a few predictable reasons, and most are about how it dried rather than a defect in the wall. The commonest causes are drying too quickly (heat, sun or draughts pulling the water out faster than the plaster can cure), being applied too thickly in one pass, shrinkage as the plaster loses water and contracts, and a weak bond to the background so the plaster moves as it sets. Fine hairline or surface crazing in the first days is common and usually cosmetic — easily filled before decorating. Cracks that are wider, that follow plasterboard joints, that keep reopening, or that come with the plaster sounding hollow point to a bond or background issue rather than simple drying. If the crack is structural — diagonal across a doorway, stepped through brickwork or growing — the plaster is just revealing movement in the building beneath it.
It is disheartening to see cracks appear in plaster you have just paid for. Most new-plaster cracks are part of normal drying and easily dealt with, but a few signal that something needs attention. Here is how to read them.
New plaster cracking — key facts
- Most common causeDrying too fast / shrinkage
- Usually harmlessFine hairline crazing
- Worth a closer lookCracks at board joints, hollow areas
- PreventionSlow, even drying; correct thickness
- Structural signDiagonal, stepped or growing cracks
Drying too fast — the most common cause
Plaster is wet when applied and has to lose that water gradually as it cures and hardens. If it dries too fast, the surface shrinks and skins over before the body of the plaster has set, and fine cracks open across the surface. The usual accelerants are:
- Heat. A radiator or heater left blasting onto fresh plaster, or central heating turned up too high too soon, drives the water out unevenly.
- Direct sun. Sun through a window onto a freshly plastered wall dries that patch faster than the rest, causing localised cracking.
- Draughts. Open windows and through-draughts pull moisture from the surface quickly while the interior is still wet.
The fix is patience and gentle conditions. Fresh plaster should be allowed to dry slowly and evenly — moderate ventilation rather than a gale, no fierce direct heat, and no rush to whack the heating up. Cracks from over-fast drying are usually fine and cosmetic, and are filled before decorating, but preventing them in the first place gives a better finish.
Applied too thick, or a weak bond
Two application factors cause more significant cracking:
- Plaster applied too thickly in one pass. Each type of plaster has a sensible thickness range. Pile it on too thick and the outside sets while the inside is still wet and shrinking, which cracks the surface; very thick coats can also slump and craze. Building out depth should be done in layers — an undercoat to build the depth, keyed and firmed up, then a thin finish — rather than one heavy coat.
- A weak bond to the background. If plaster is applied over a dusty, oily, painted, flaky or wrongly prepared surface, or onto a background with the wrong suction, it may not key properly. As it sets and shrinks it pulls away in places, cracking the surface and sometimes blowing (sounding hollow). Low-suction backgrounds need the right undercoat or a bonding agent; high-suction backgrounds may need controlling so they do not rob the plaster of water.
Cracks from these causes are more likely to be wider, to recur after filling, or to coincide with hollow-sounding areas, because they reflect a genuine problem with how the plaster is sitting on the wall rather than just surface drying.
Movement, joints and the wall beneath
Some cracks in new plaster have nothing to do with the plastering itself — the plaster is simply revealing what the structure behind it is doing:
- Plasterboard joint cracking. Where new plaster skims over plasterboard, cracks can appear along the joints between boards if the joints were not properly taped and reinforced, or as the boards and timber behind them move with temperature and humidity. These are typically straight cracks running along the line of a board edge.
- Background movement. Timber framing, lath, and new structural elements all move as they settle and as humidity changes. New plaster bridging a junction between two different materials — say timber and masonry — often cracks along that junction.
- Structural movement. A diagonal crack running from the corner of a door or window, a stepped crack that also shows in the brickwork, or any crack that grows over weeks, indicates movement in the building. The new plaster did not cause it; it is showing it. These are the cracks to take seriously and, if they grow, to have assessed by a surveyor.
Distinguishing these from drying cracks is mostly about pattern and behaviour: drying cracks are fine and random; joint cracks are straight and follow board edges; structural cracks are wider, directional and grow.
Preventing and repairing new-plaster cracks
Most new-plaster cracking is preventable and, where it does occur cosmetically, easily repaired.
Prevention:
- Let plaster dry slowly and evenly — moderate ventilation, no fierce heat, no direct sun on the fresh surface, no high central heating for the first days.
- Build out depth in correct-thickness coats rather than one thick pass.
- Prepare and prime the background so the plaster bonds; match the undercoat to the suction of the wall.
- Tape and reinforce plasterboard joints and dissimilar-material junctions before skimming.
Repair:
- Fine cosmetic cracks: let the plaster dry fully, then fill with a flexible filler, sand, seal new plaster with a mist coat, and decorate.
- Recurring or joint cracks: rake out, reinforce with flexible jointing tape or scrim, fill and finish; flexible decorator's caulk suits junctions that move slightly.
- Cracks over hollow / blown areas: the affected plaster usually needs cutting out and re-doing with proper preparation rather than just filling.
- Structural cracks: do not just fill and paint — get the movement assessed first, because filling hides the symptom and the crack returns.
Frequently asked questions
Is it normal for new plaster to crack a little?
Fine hairline crazing on freshly plastered surfaces is common and usually harmless, caused by drying shrinkage. It is filled and painted over once the plaster has dried fully. Cracking only suggests a problem when cracks are wider, keep reopening after filling, follow plasterboard joints, or coincide with areas that sound hollow when tapped.
How do I stop new plaster from cracking as it dries?
Let it dry slowly and evenly. Avoid fierce direct heat, do not turn the central heating up high in the first few days, keep direct sun off the fresh surface, and use moderate ventilation rather than strong draughts. Building out depth in correct-thickness coats rather than one thick pass, and preparing the background so the plaster bonds, also reduces cracking.
When should I worry about cracks in new plaster?
Be cautious when a crack runs diagonally from the corner of a door or window, steps through the brickwork as well as the plaster, or is visibly growing over weeks — these indicate structural movement that the plaster is revealing rather than causing. Wide cracks over hollow-sounding areas also point to a bond failure that needs the plaster cut out and redone rather than simply filled.
Sources & further reading
- British Gypsum — plastering and drying guidance
- The Federation of Plastering and Drywall Contractors — best practice
- RICS — cracking and movement in buildings
Figures on this page are typical UK ranges drawn from published sources and depend on your specific room. They are guidance, not a quotation.