Repairing Cracks in Plasterboard: A Complete Guide

If you've noticed a crack running across a wall or ceiling in your home, you're probably wondering whether it's a quick DIY fix or a sign of something more serious. Repairing cracks in plasterboard is one of the most common jobs we're called out for across London, from hairline cracks along joints in a Victorian terrace to larger splits caused by settlement in a newer flat. The good news is that most plasterboard cracks are straightforward to repair once you understand what's causing them and which method suits the type of crack you're dealing with.

This guide walks through everything a London homeowner or landlord needs to know: why these cracks appear, how to repair them properly, what materials to use, and when it makes more sense to bring in a professional rather than reaching for the filler yourself.

What Causes Cracks in Plasterboard?

Before repairing cracks in plasterboard, it helps to understand why they appear in the first place, because the cause affects the repair method.

Joint cracks are the most common type. These occur along the seams where two sheets of plasterboard meet, usually because the jointing tape and compound weren't applied correctly, or the board has moved slightly over time. You'll often see these as a thin, straight line running the length of a wall or across a ceiling.

Settlement cracks happen as a building naturally moves and settles, particularly common in older London properties such as Victorian terraces and Edwardian semis where timber joists and foundations have had decades to shift. These cracks tend to appear at corners, above doorways, and around window frames.

Impact damage causes more irregular cracking, often radiating outward from a single point where something has knocked the wall, like furniture being moved or a doorknob hitting the plasterboard repeatedly.

Temperature and humidity changes cause plasterboard and the surrounding timber or metal studwork to expand and contract, which can open up hairline cracks, particularly in properties with poor insulation or inconsistent heating.

Structural movement is the one to watch for. If cracks are widening, appear diagonally, or are accompanied by doors and windows sticking, this could indicate a more serious structural issue rather than a simple plasterboard problem.

Why Repairing Cracks in Plasterboard Matters for London Properties

London's housing stock is a genuine mix of eras, and each comes with its own quirks when it comes to plasterboard cracking. Victorian terraces often have a combination of original lath and plaster alongside later plasterboard additions from renovations, meaning cracks can appear where old and new materials meet and move differently. Edwardian semis frequently show settlement cracking around bay windows and chimney breasts. Modern flats and new-builds, meanwhile, often experience joint cracking in the first year or two as the building completes its initial settling period, sometimes called 'snagging' cracks.

Leaving cracks unattended isn't just a cosmetic issue. Gaps in plasterboard can let draughts through, undermine the acoustic performance of a wall, and in some cases allow moisture to get behind the board, which can lead to more significant damage over time. For landlords, unresolved cracks can also affect how a property presents to tenants and potential buyers, so addressing them promptly is generally worthwhile both for appearance and for protecting the fabric of the building.

(/PlasterboardCostLondon) joint in a London period property, with a utility knife and filling knife laid beside it ready for repair]

Types of Cracks and Repair Options

Not every crack needs the same treatment. Broadly, plasterboard cracks fall into a few categories, each with a suitable repair approach:

Hairline cracks (under 2mm wide) can usually be filled directly with a flexible filler or jointing compound, sanded back, and painted over. These are the simplest repairs and are well within reach for most confident DIYers.

Joint line cracks typically need the tape re-bedding and re-skimming. Simply filling over a joint crack without addressing the tape underneath often results in the crack reappearing within months.

Wider or recurring cracks (above 5mm, or ones that keep coming back after filling) usually indicate movement in the board itself or the studwork behind it. These often need the crack opened out, scrim tape applied, and a proper skim coat over the top, sometimes requiring a small section of board to be cut out and replaced entirely.

Cracks from impact damage with surrounding board damage are closer to a patch repair than a simple crack fill, and may need a cut-out section of new plasterboard fitted before skimming.

If you're dealing with cracks specifically on a ceiling rather than a wall, the approach is broadly similar but often needs extra care due to the weight and angle involved, and persistent ceiling cracks can sometimes point to joist movement rather than a plasterboard problem alone.

How Repairing Cracks in Plasterboard Works: Step-by-Step

The process for fixing cracks in plasterboard follows a fairly consistent sequence, whether the crack is small or more substantial:

1. Assess the crack. Check the width, length, and whether it's a straight joint line or an irregular impact crack. Press gently around the area to see if the board feels loose or spongy, which could indicate water damage behind it.

2. Rake out and widen the crack. Using a utility knife or scraper, open the crack slightly into a shallow V-shape. This gives the filler or compound something to key into, rather than sitting on the surface where it's more likely to crack again.

3. Remove dust and debris. A dry brush or vacuum works well here. Any dust left in the crack will stop the filler bonding properly.

4. Apply scrim tape for anything beyond a hairline crack. Self-adhesive fibreglass scrim tape bridges the gap and prevents the crack reappearing. This step is often skipped by inexperienced DIYers and is the main reason cracks come back after a quick filler job.

5. Apply jointing compound or filler. Build it up in thin layers rather than one thick application, allowing each layer to dry before adding the next. This reduces shrinkage cracking as the compound cures.

6. Sand back. Once fully dry, sand the area flush with the surrounding wall or ceiling using a fine-grit sanding block.

7. Skim or texture to match. Depending on the original wall finish, this might mean a thin skim coat with a plastering trowel, or matching an existing texture such as artex.

8. Prime and paint. Filled and skimmed areas are porous and will show through paint unmatched unless primed first with a mist coat or appropriate sealer.

For larger cracks or where sections of board have failed, a plasterboard repair patch may be the more appropriate solution rather than attempting to fill a crack that's really a sign the board itself needs replacing in that section.

Materials and Considerations

Getting the materials right makes a noticeable difference to how long a repair lasts.

Fillers vs jointing compound: Standard decorator's filler works fine for small, stable hairline cracks, but for joint lines and anything likely to move, a proper jointing compound (sometimes called joint filler or finishing compound) combined with scrim tape gives a far more durable result.

Flexible fillers: For cracks in areas prone to movement, such as above doorframes or around loft hatches, a flexible, slightly elastic filler can help absorb minor ongoing movement without cracking again straight away.

Scrim tape: Self-adhesive fibreglass mesh tape is essential for anything beyond a hairline crack. It's inexpensive and makes a genuine difference to the longevity of the repair.

Matching existing texture: Many London properties, particularly those renovated in the 1980s and 90s, still have artex ceilings or textured finishes. Matching this convincingly after a crack repair takes practice, and a mismatched patch can be more visible than the original crack.

Paint and primer: Always use a mist coat (diluted matt emulsion) over fresh filler or skim before applying a full coat of paint, otherwise the repair will show through as a dull, flat patch under the sheen of the surrounding paint.

Choosing the Right Approach

The right method depends largely on the size and cause of the crack. A single, stable hairline crack on a wall you plan to repaint anyway is a reasonable DIY job for most people with basic tools and a bit of patience. Recurring cracks, wider splits, cracks on ceilings, or anything near a structural element like a chimney breast or load-bearing wall are better handled by someone experienced, particularly because misdiagnosing a structural crack as a simple cosmetic one can lead to repeat call-outs and wasted materials.

If you're repairing multiple cracks across a room, or the plasterboard itself seems to be failing in several places, it may be more cost-effective to consider a fuller re-skim of the wall or ceiling rather than patching crack by crack, especially if the existing finish is old, cracked in several places, or doesn't match modern plasterboard specifications. Similarly, if you're planning other work such as improving insulation or soundproofing, it's worth looking at insulated plasterboard or acoustic plasterboard options rather than simply patching the existing board.

When to Use Professional Plastering Services

DIY crack repairs can work well for small, isolated, stable cracks, but there are situations where calling in a professional plasterer makes more sense:

• Cracks that keep reappearing after filling, suggesting an underlying issue with the board or studwork
• Cracks accompanied by other signs of movement, such as sticking doors, gaps around skirting, or cracks in brickwork outside
• Ceiling cracks, which carry more risk if the board is failing and can be trickier to blend invisibly
• Multiple cracks across a room, where a full re-skim may be more practical and cost-effective than patch repairs
• Properties being sold or let, where a smooth, professional finish matters for presentation
• Older London properties where lath and plaster meets plasterboard, requiring different techniques to get a seamless result

As a family-run plastering company with over 20 years of experience across all 32 London boroughs, we regularly deal with everything from a single hairline crack in a Clapham flat to full re-skims in Victorian terraces in Walthamstow. If you're unsure whether your crack is a quick fix or something that needs a closer look, it's generally worth getting a professional opinion before committing to a DIY repair that might not last.

Maintaining the Results

Once a crack has been properly repaired, there are a few simple things that help prevent it coming back. Try to keep indoor humidity reasonably consistent, particularly in older properties without modern insulation, since large swings in temperature and moisture are a common cause of recurring hairline cracking. Avoid hanging heavy items directly over a repaired area without proper wall fixings, and keep an eye on any repair over the following few months, since compound can shrink very slightly as it fully cures, sometimes needing a light touch-up coat. If a repaired crack reopens in exactly the same spot, it's usually a sign of ongoing structural movement rather than a failed repair, and worth having assessed properly.

FAQ About Repairing Cracks in Plasterboard

What is repairing cracks in plasterboard and when is it needed? Repairing cracks in plasterboard involves filling, taping, and finishing splits or hairline cracks in plasterboard walls or ceilings. It's needed whenever a crack appears, whether from board movement, impact damage, settlement, or ageing joint tape, to stop the gap widening and to restore a smooth, paintable surface.

How much does repairing cracks in plasterboard cost in London? Costs vary depending on the size, number, and location of cracks, as well as whether scaffolding or access equipment is needed for ceiling work. Small, isolated cracks are generally much cheaper than multiple cracks requiring a fuller re-skim, so it's best to get a quote based on your specific situation.

How long does repairing cracks in plasterboard take? A single small crack can often be filled, sanded, and ready to paint within a day, accounting for drying time between coats. Larger cracks needing scrim tape and a skim coat, or multiple cracks across a room, typically take longer due to drying times between each stage, often spread across a couple of days for the best finish.

Can I do repairing cracks in plasterboard myself or should I hire a professional? Small, stable hairline cracks are a reasonable DIY job with basic tools, filler, and patience. Wider, recurring, or ceiling cracks, and anything suggesting structural movement, are better handled by an experienced plasterer to avoid a repair that fails again within months.

What are the alternatives to repairing cracks in plasterboard? If a board has multiple cracks, is sagging, or has suffered water damage, replacing the damaged section with new plasterboard may be more effective than repeated patch repairs. For rooms with widespread cracking, a full re-skim of the wall or ceiling is often more cost-effective and longer-lasting than patching numerous individual cracks.

How do I maintain the results after a crack repair? Keep indoor humidity and temperature reasonably stable, avoid heavy impacts near the repaired area, and check the repair after a few months for any shrinkage that might need a light touch-up. If the same crack reopens in the same spot, it usually points to ongoing movement rather than a failed repair technique.

Getting Help With Plasterboard Cracks in London

Repairing cracks in plasterboard properly comes down to correctly diagnosing the cause, using the right materials for the size of the crack, and taking the time to let each stage dry before moving to the next. For small, stable hairline cracks, a careful DIY approach with filler and a bit of patience can work well. For anything wider, recurring, or affecting a ceiling, getting an experienced eye on it first can save time, materials, and repeat repairs down the line.

If you're searching for "plasterers in my area" across London and want a second opinion on a crack, or need a full room re-skim rather than patching crack by crack, London Plastering Service has over 20 years of experience working across all 32 London boroughs, from Victorian terraces to modern flats. You can reach us on +44 7460 892826 or at office@londonplasteringservice.com, Monday to Friday 7am-7pm and Saturday 8am-5pm, for advice or a quote tailored to your property.