cracked plaster

Quick Answer: Most plastering problems stem from poor preparation, incorrect mixing ratios, or rushing the drying process. The most common issues include cracking (caused by rapid drying, structural movement, or inadequate keying), delamination (poor suction control or contaminated backgrounds), bubbling (trapped air or moisture), and staining (water ingress or soluble salts). While minor surface cracks and small patches are DIY-friendly, extensive cracking, structural issues, or damp-related problems require professional assessment. Proper diagnosis is essential — treating symptoms without addressing the root cause will lead to recurring failures. 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. Pro Tip: Never apply heat to accelerate drying in the first 48 hours. British Gypsum recommends maintaining temperatures between 13-18°C with good ventilation. Use a dehumidifier if conditions are humid, but avoid direct heat sources like fan heaters pointed at fresh plaster. 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 ⚠️ Warning: Settlement cracks wider than 5mm, horizontal cracks in walls, or cracks that continue to widen require immediate structural engineer assessment. Don’t plaster over potentially dangerous structural defects. Building Regulations Part A (Structure) must be satisfied before cosmetic repairs. 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,