Understanding Why Plastering Problems Occur
After thirty years in the trade, I can tell you that most plastering defects aren’t random — they follow predictable patterns. The majority of problems I encounter on remedial jobs could have been prevented with proper preparation, correct material selection, and adequate drying time.
Plastering is a system, not just slapping gypsum on a wall. Every component matters: the background substrate, the bonding agent, the plaster mix, ambient conditions, and the finishing technique. When one element fails, the entire system can break down.
Understanding the root cause of plastering problems is crucial because treating symptoms without fixing the underlying issue leads to recurring defects. A crack filled with decorator’s caulk will reappear if structural movement continues. Stains will bleed through fresh paint if the moisture source isn’t eliminated.
The Most Common Plastering Problems
Based on thousands of remedial jobs across Kent, these are the defects I encounter most frequently:
- Cracking — from hairline surface crazing to structural cracks several millimetres wide
- Delamination — plaster losing adhesion and hollowing from the substrate
- Bubbling and blistering — trapped air or moisture creating raised areas
- Staining and discolouration — brown patches, efflorescence, or yellow marks bleeding through
- Poor finish quality — uneven surfaces, trowel marks, ridges, or excessive porosity
- Slow drying or persistent dampness — walls remaining soft or dark weeks after plastering
- Crumbling or powdery surfaces — weak plaster that dusts off or won’t take paint
Let’s examine each problem in detail, diagnose the causes, and provide professional-grade solutions that actually work.
Cracking: Types, Causes, and Solutions
Not all cracks are created equal. The pattern, width, and location tell an experienced plasterer exactly what’s gone wrong. According to BRE (Building Research Establishment) guidance, cracks wider than 2mm indicate potential structural issues requiring investigation before cosmetic repairs.
Map Cracking (Crazing)
These fine surface cracks create a random network pattern resembling a road map. They’re typically shallow — less than 1mm deep — and purely cosmetic.
Common causes:
- Excessive trowelling or over-working the surface during finishing
- Too-rapid drying due to hot weather, direct sunlight, or forced heating
- Incorrect water content in the final mix (too wet or too dry)
- Applying finishing plaster over an excessively porous background without proper suction control
- Using expired or contaminated plaster (British Gypsum products have a 4-month shelf life from manufacture)
Professional fix: For minor crazing on multi-finish or board finish, a light mist-coat with diluted PVA (1:5 ratio) followed by a thin skim of fresh plaster will fill the network. For deeper crazing, scrape out loose material, apply a bonding agent, and patch with finishing plaster matched to the existing surface.
Settlement Cracks
These are straight or diagonal cracks, typically running from ceiling corners or around door frames. They indicate structural movement in the building fabric.
Common causes:
- New build settlement (normal in properties under 12 months old)
- Foundation subsidence or heave due to clay soil movement
- Thermal expansion and contraction (especially in buildings with inadequate expansion joints)
- Lintel deflection above openings
- Removal of load-bearing walls without proper support
Professional fix: Monitor cracks for 6-12 months using tell-tales (glass or plastic markers). If movement has ceased, rake out cracks to 10mm depth, fill with a flexible filler like Everbuild StixAll or CT1, then apply scrim tape before skim coating. For active cracks, flexible crack bridging systems are necessary. For further guidance on structural concerns, our article on why plaster cracks and prevention methods covers this in depth.
Shrinkage Cracks
These appear as the plaster cures, typically within 24-72 hours. They often run along joints between plasterboards or where different materials meet.
Common causes:
- Excessively thick coats (over 15mm in one application)
- High-suction backgrounds not adequately controlled
- Rapid moisture loss during curing
- Missing or improperly installed scrim tape at board joints
- Incompatible backing materials with different expansion coefficients
Professional fix: Prevention is key. Apply proper scrim tape to all plasterboard joints before the first coat. For remedial work, cut out the crack in a V-shape, apply scrim, and fill with easy-fill compound (Gyproc EasiFill is excellent for this). Two thin coats are always better than one thick application.
Delamination and Hollow Plaster
Delamination occurs when plaster loses adhesion to the background substrate. You’ll hear a hollow sound when tapping affected areas — a dead giveaway that the plaster’s about to fail catastrophically.
Primary causes:
- Poor suction control — plastering onto bone-dry backgrounds or non-absorbent surfaces without proper preparation
- Contaminated substrates — dust, paint, wallpaper paste, or grease preventing mechanical key
- Wrong backing coat — using finishing plaster on unsuitable backgrounds (it needs undercoat plaster or bonding first)
- Frozen plaster — mixing or applying below 5°C causes crystals to form, destroying bond strength
- Movement differential — new plaster applied over incompatible materials (timber to masonry transitions without proper detailing)
| Background Type | Preparation Required | Bonding Agent |
|---|---|---|
| Painted walls | Remove loose paint, score surface, wash down | Blue Grit or Thistle Bond-It |
| Engineering bricks | Hose down to saturate | Thistle Bond-It neat coat |
| Plasterboard (grey side) | Check all fixings, tape joints | None (direct application) |
| Old lime plaster | Remove loose material, brush clean | Lime-compatible primer |
| Dense concrete blocks | Wire brush, dampen | Bonding coat or SBR slurry |
Professional fix: Hollow plaster must be removed completely — there’s no shortcut. Chip out all loose material back to solid substrate using a bolster chisel and club hammer. Prepare the background properly (see table above), then rebuild using appropriate backing coats. For small areas under 300mm², Gyproc EasiFill works well. Larger areas need proper backing plaster (Hardwall or Browning) followed by a 2-3mm skim of multi-finish.
Bubbling, Blistering, and Surface Defects
Bubbles and blisters indicate trapped air or moisture beneath the plaster skin. They can appear during application or develop days later as the plaster cures.
Immediate bubbling (during application):
- Mixing plaster too vigorously, incorporating excessive air
- Adding plaster to water instead of the correct method (always add plaster to water, never the reverse)
- Working plaster that’s started to go off (British Gypsum plasters have 60-90 minute working times)
- Applying over dusty or contaminated surfaces
Delayed blistering (after setting):
- Moisture trapped behind plaster from damp walls
- Condensation forming on cold external walls
- Plumbing leaks within the wall cavity
- Rising damp wicking through masonry
Professional fix: For air bubbles during application, remix plaster properly — sprinkle gypsum plaster into clean water (never reuse water) and hand-mix or use a paddle mixer at low speed. For delayed blisters, diagnose and eliminate the moisture source first. Use a damp meter to map affected areas. If moisture readings exceed 18% on a timber/gypsum scale, investigate thoroughly before any remedial plastering. Our guide on complete plastering preparation covers moisture management in detail.
Staining and Discolouration Issues
Stains bleeding through fresh plaster are both aesthetically displeasing and diagnostically significant. The type and pattern of staining reveals the underlying problem.
Brown Water Stains
These indicate active water ingress — either from above (roof leaks, bathroom spillage) or penetrating damp through walls.
Professional fix: Identify and eliminate the water source first. Use a moisture meter and thermal imaging camera to map the extent. Once dry (below 16% moisture content), seal the stained area with Zinsser BIN primer before plastering. Never plaster over active leaks — it’s guaranteed to fail.
Yellow or Brown Nicotine Staining
Common in properties with long-term smoking or soot deposits from open fires. These stains are oil-based and bleed through water-based paints and thin plaster.
Professional fix: Wash surfaces with sugar soap, rinse thoroughly, and apply two coats of Zinsser BIN or Coverstain before plastering. For severe contamination, overboard with 9.5mm plasterboard to create a clean substrate.
White Efflorescence (Salt Deposits)
Crusty white deposits appearing on plaster surfaces indicate soluble salts migrating from the substrate. Common in properties with historical damp issues or following flood damage.
Professional fix: Brush off deposits (they’re typically sodium or calcium salts). Test with a damp meter — if moisture levels are normal but salts persist, apply a salt-inhibiting primer like Remmers Sulfatex. For severe cases, use specialist renovation plaster systems designed for salt-contaminated substrates (Remmers Sanierputz or similar). Standard gypsum plasters will continue to break down in high-salt environments.
Poor Finish Quality Problems
These are largely skill-related defects but understanding why they occur helps DIY enthusiasts know when to call professionals.
| Defect | Cause | Solution |
|---|---|---|
| Trowel marks and ridges | Insufficient trowelling passes, wrong timing | Apply thin water coat, re-trowel when firm |
| Uneven thickness | No depth guides (screeds), poor technique | Strip back and re-plaster with proper screeds |
| Rippled surface | Mix too wet, applied too thick | Sand flat when dry, skim over |
| Rough, open texture | Insufficient trowelling, mix too dry | Apply thin coat of easy-fill, sand smooth |
| Visible joints in skim | Plaster gone off, unable to blend edges | Cut back to clean edges, re-skim sections |
When to call a professional: If you’re achieving consistently poor finishes or struggling with technique, professional plastering typically costs £200-400 for an average room in Kent (as of 2026). That’s far cheaper than repeatedly buying materials and spending weekends frustrated with poor results.
Damp-Related Plastering Problems
Moisture is the silent killer of plasterwork. According to the Property Care Association, inappropriate plastering over damp walls accounts for millions of pounds in remedial work annually across the UK.
The golden rule: never plaster over damp walls. Gypsum plaster is hygroscopic and will wick moisture, remaining soft indefinitely and providing ideal conditions for mould growth.
Types of damp affecting plastering:
- Rising damp — moisture rising through masonry by capillary action (typically up to 1.2m above ground level)
- Penetrating damp — water ingress through walls, roofs, or around windows
- Condensation — excess humidity condensing on cold surfaces (especially in poorly ventilated rooms)
- Plumbing leaks — hidden pipe failures within walls or floor voids
Professional diagnosis and fix: Use a calibrated moisture meter (pin-type and radio frequency) to map moisture distribution. Readings above 20% WME (Wood Moisture Equivalent) indicate investigation is needed. Address the source: install DPCs, repair roofs, upgrade ventilation, fix leaks. Only when readings consistently fall below 16% should plastering commence. Consider using renovation plasters with built-in moisture management for marginal cases.
Timing-Related Problems
Many plastering failures stem from impatience. Modern construction schedules put pressure on trades to work faster, but plaster chemistry can’t be rushed.
Plaster Applied Too Soon After Construction
New blockwork, fresh concrete, and green timber contain substantial construction moisture. Plastering before adequate drying causes defects.
Recommended waiting times:
| Substrate | Minimum Drying Period | Before Plastering |
|---|---|---|
| Dense concrete blocks | 6-8 weeks | Use moisture meter, aim for <16% WME |
| Lightweight aircrete blocks | 2-3 weeks | Lower moisture content acceptable |
| Cement render (backing coat) | 7-10 days per 10mm thickness | Must be firm, not soft |
| Plasterboard (dry-lining) | Immediate | No waiting required |
| Bonding coat (undercoat plaster) | 24 hours minimum | Must be completely set and firm |
Decorating Too Soon After Plastering
Fresh plaster needs adequate curing time before decoration. Rushed painting traps moisture, prevents proper carbonation, and causes paint failure.
Safe decoration timings:
- Mist coat application — minimum 7-10 days after final skim (plaster should be uniformly light pink, no dark patches)
- Full decoration — 2-4 weeks depending on coat thickness, ventilation, and ambient conditions
- Oil-based paints — minimum 8 weeks (gypsum plaster has high pH which can saponify oils)
- Wallpaper application — 4-6 weeks (paste can re-wet plaster causing expansion and bubbling)
Our detailed guide on how long to leave plaster before painting covers this comprehensively.
Material Quality and Storage Issues
Even experienced tradesmen can encounter problems from degraded materials. Gypsum plaster has a finite shelf life, and improper storage accelerates deterioration.
Signs of degraded plaster:
- Lumpy texture that won’t break down when mixed
- Rapid setting (plaster goes off in under 30 minutes)
- Very slow setting (still soft after 4+ hours)
- Poor final strength (can be scraped easily with fingernail)
- Excessive expansion or shrinkage during setting
Proper storage guidelines: Store plaster bags on pallets, never directly on concrete floors. Keep in dry conditions (relative humidity below 70%). Use oldest stock first (rotate inventory). Once opened, reseal bags tightly or transfer to airtight containers. British Gypsum specifies 4 months shelf life from manufacture, but in poor storage conditions, degradation can occur within weeks.
Current pricing (2026): Multi-finish plaster costs £8-12 per 25kg bag from builders’ merchants like Jewson, Travis Perkins, or Screwfix. Buying degraded or expired plaster to save £2-3 is false economy — the labour cost of replastering a failed job is £200-400 minimum.
Structural vs. Cosmetic Problems: When to Worry
Not every crack requires emergency intervention, but knowing the difference between cosmetic defects and structural warning signs is crucial.
Cosmetic problems (DIY-repairable):
- Hairline cracks less than 1mm wide, not widening
- Surface crazing or map cracking
- Minor staining from historical damp (now resolved)
- Small patches of delamination under 100mm diameter
- Finish imperfections (trowel marks, slight unevenness)
Structural concerns (professional assessment required):
- Cracks wider than 3mm, especially if stepped or diagonal
- Horizontal cracks in walls or ceiling-wall junctions
- Cracks that reappear after repair
- Bulging or bowing walls
- Separation between walls and adjacent structures
- Cracks accompanied by sticking doors/windows or floor level changes
According to RICS (Royal Institution of Chartered Surveyors) guidance, cracks showing progressive movement should be monitored by qualified structural engineers. Insurance claims for structural damage often depend on documented evidence of movement patterns.
DIY Repairs vs. Professional Help
Many homeowners can tackle minor plastering repairs successfully with proper preparation and realistic expectations. However, certain jobs demand professional expertise.
Suitable for competent DIY:
- Filling small cracks and holes under 50mm diameter
- Repairing minor surface damage
- Skim coating plasterboard for dry-lining projects
- Small patch repairs using ready-mixed compounds
- Surface preparation and priming
Requires professional plasterers:
- Full room re-plastering or large area repairs (over 3m²)
- Two-coat work (backing coat plus skim)
- Ceiling plastering (overhead work requires technique and stamina)
- Period property restoration requiring lime plaster
- Damp-related issues requiring specialist renovation plasters
- Structural crack repairs with movement accommodation
Professional plasterers in Kent typically charge £150-250 per day labour plus materials. For a standard 4m x 4m room re-skim, expect £300-500 total. While this seems expensive compared to DIY, consider that professional work comes with implicit guarantees, insurance coverage, and decades of technique refinement you simply can’t replicate from YouTube videos.
Preventive Measures: Stopping Problems Before They Start
The best repair is the one you never need to do. Following proper protocols dramatically reduces plastering failures.
Essential prevention checklist:
- Substrate preparation — clean, sound, correctly primed backgrounds are non-negotiable
- Environmental control — maintain 13-18°C during application and curing, ensure adequate ventilation
- Material quality — use fresh, properly stored materials from reputable suppliers (British Gypsum, Knauf, Siniat)
- Correct mixing — follow manufacturer ratios precisely (typically 11.25 litres water per 25kg bag for multi-finish)
- Appropriate products — match plaster type to substrate and exposure conditions
- Adequate drying — never rush decoration or subsequent trades
- Movement accommodation — use scrim tape at material transitions and expansion joints in large areas
Building Regulations Approved Document B (Fire Safety) also specifies requirements for plaster thickness and fire resistance in certain applications. Ensure compliance — it’s not just about aesthetics.
Essential Tools and Materials for Repairs
Having the right kit makes plastering repairs significantly easier and more successful.
Basic repair toolkit:
- Filling knife — 75mm and 150mm widths (Marshalltown or similar, £8-15 each from Screwfix)
- Plastering trowel — 280mm stainless steel (£25-40 for decent quality)
- Hawk — 330mm aluminium (£15-25)
- Mixing bucket — 25-litre capacity (£5-8)
- Plasterer’s brush — for dampening and cleaning (£6-10)
- Sanding block — 120-grit abrasive for feathering edges (£5-12)
- Moisture meter — for diagnostics (entry-level models £30-60)
- Bolster chisel and club hammer — for removing defective plaster (£15-25 total)
Materials for common repairs:
- Easy-fill compound — Gyproc EasiFill (£8-12 per 10kg tub, covers approximately 7-10m² at 2mm thickness)
- Multi-finish plaster — Thistle Multi-Finish (£8-12 per 25kg bag)
- Bonding agents — Blue Grit or Thistle Bond-It (£15-20 per 5-litre container)
- Scrim tape — self-adhesive fibreglass mesh (£3-5 per 45m roll)
- Flexible filler — Everbuild StixAll or CT1 for movement joints (£8-15 per tube)
- Stain-blocking primer — Zinsser BIN or Coverstain (£25-35 per litre)
Cost Comparison: Repair vs. Replace
Sometimes wholesale replastering makes more economic sense than extensive patch repairs.
| Scenario | Repair Cost (Kent, 2026) | Re-plaster Cost | Recommendation |
|---|---|---|---|
| Minor crack repair (under 1m length) | £80-150 (2 hours labour) | N/A | Repair |
| Multiple cracks, room-wide | £250-400 (extensive patching) | £400-600 (full skim) | Re-plaster |
| Delamination patches (<10% wall area) | £150-300 | N/A | Repair |
| Widespread delamination (>30%) | £400-700 (extensive removal) | £500-800 (strip and re-plaster) | Re-plaster |
| Damp-damaged plaster | Variable (damp treatment first) | £600-1,200 (including remedial work) | Strip to substrate, treat damp, re-plaster |
Material costs are relatively minor — a 25kg bag of multi-finish covers approximately 9-10m² at 2mm thickness. Labour dominates pricing. Professional plasterers price by the day or by floor area, with typical rates of £30-45 per m² for skim coating or £150-250 daily rate.
Regional Considerations for Kent Properties
Kent’s diverse housing stock — from Victorian terraces in Maidstone to post-war estates in Medway towns — presents specific challenges.
Common Kent-specific issues:
- London Clay subsidence — particularly in north Kent areas, causing seasonal movement and cracking
- Coastal properties — salt-laden air in Whitstable, Herne Bay, and Margate accelerates plaster degradation
- Period properties — many Victorian/Edwardian properties in Canterbury and Tunbridge Wells have lime plaster that shouldn’t be patched with modern gypsum
- Post-war no-fines concrete — some 1950s-1960s estates used no-fines concrete construction requiring specialist plastering systems
Local building control officers (Kent County Council and individual district councils) can provide specific guidance for listed buildings and conservation areas, where inappropriate repairs can affect property values and planning compliance.
Frequently Asked Questions
How do I know if a crack is serious or just cosmetic?
Crack width and pattern are key indicators. Hairline cracks under 1mm that aren’t widening are typically cosmetic settlement. Cracks wider than 3mm, stepped cracks following mortar joints, or horizontal cracks in walls suggest structural movement requiring professional assessment. Use a crack width gauge (available for £5-10 from tool suppliers) to monitor width over several months. If a crack widens by more than 1mm over 6 months, consult a structural engineer before any cosmetic repairs.
Can I plaster over paint without removing it first?
It depends on the paint condition and type. Loose, flaking, or glossy paint must be removed or the plaster won’t bond. For sound matt emulsion, scuff the surface with coarse sandpaper (40-60 grit), wash with sugar soap, rinse, and apply a bonding agent like Blue Grit or Thistle Bond-It. For gloss or silk finishes, either remove completely or apply a mechanical key (score with a scarifier) plus bonding agent. The effort saved by not stripping paint is minimal compared to the cost of failed plasterwork.
Why does my plaster keep cracking in the same place?
Recurring cracks indicate an underlying issue that hasn’t been addressed. Common causes include ongoing structural movement (subsidence, thermal expansion), moisture cycling (damp getting in during winter, drying in summer), or missing expansion joints at material transitions. Simply filling the crack treats the symptom, not the cause. Monitor the crack width with tell-tales, check for moisture with a damp meter, and consider whether building movement has been properly investigated. For active cracks, flexible crack-bridging systems or movement joints may be necessary.
How long should I wait before painting new plaster?
Minimum 7-10 days for the first mist coat, but this varies with conditions. Plaster should be uniformly light pink with no dark patches before decoration. Thick coats (over 10mm total) may need 2-3 weeks. In humid conditions or poorly ventilated rooms, extend this to 3-4 weeks. Use a moisture meter to verify — readings should be below 16% WME before painting. Rushing decoration is one of the most common causes of paint failure, blistering, and mould growth. Our comprehensive guide on drying times and decoration covers this in detail.
Is it better to patch damaged plaster or re-skim the entire wall?
For isolated damage covering less than 10% of the wall area, patching is cost-effective and practical. For widespread damage, multiple patches, or severely uneven surfaces, a full re-skim provides better results and often costs less than extensive patching labour. Consider that patched areas may show slight texture differences under raking light, particularly with large or numerous patches. As a general rule, if you’re patching more than 30% of a wall area, re-skimming the entire surface makes more sense aesthetically and economically.
Can I use decorators’ filler instead of proper plaster for repairs?
For very small holes and cracks (under 10mm wide and shallow), decorators’ filler (Polyfilla, Toupret, etc.) works adequately. However, these products aren’t designed for structural repairs or large areas. They’re typically more expensive per litre than plaster, have limited working time, and can’t be built up in layers like plastering compounds. For anything beyond minor cosmetic filling, use appropriate plastering materials: easy-fill compound for small patches, one-coat plaster for medium repairs, or proper backing coat plus skim for substantial work. The right material for the job ensures durability and value.
What should I do if I discover damp behind failed plaster?
Stop all plastering work immediately and investigate the moisture source. Use a moisture meter to map the affected area and identify the type of damp (rising, penetrating, or condensation). Never plaster over damp — it will fail again and potentially cause structural timber damage. Address the root cause first: install/repair damp-proof courses, fix roof leaks, improve ventilation, or repair plumbing. Once the source is eliminated, allow the wall to dry thoroughly (below 16% moisture content) before replastering. This may take several weeks or months depending on wall thickness and construction type. Consider specialist renovation plasters for marginal cases where some background moisture is unavoidable.