Internal Defects & Finishes
Internal Cracking
Internal cracking in Class 2 buildings encompasses a wide range of crack types — from minor hairline shrinkage cracks in new plasterboard joints through to structural cracking in load-bearing walls and slabs. Accurate classification of internal cracking is essential: hairline cracks may require no more than cosmetic repair, while active structural cracks require engineering assessment and may indicate foundation movement, slab deflection or structural deficiency. Recurring cracks after patching are a reliable indicator of active movement that must be addressed before cosmetic reinstatement.
Common Signs
- Hairline to fine cracks in plasterboard joints and ceiling corners
- Diagonal cracks at window and door corners
- Cracks at the junction of walls and ceilings
- Stair-step cracking in masonry block partitions
- Cracks that are wider at one end — indicating ongoing movement
- Door and window frames binding or sticking
- Cracks recurring after previous patching
Common Causes
- Plasterboard joint shrinkage from drying after installation
- Structural slab deflection transferring stress to partition walls
- Differential settlement causing diagonal cracking at openings
- Thermal and moisture movement in masonry partitions without control joints
- Inadequate fixing of plasterboard to framing causing joint cracking
- Vibration from construction or traffic loading
- Corrosion of reinforcement causing expansive cracking in concrete walls
Risk of Neglect
- Structural cracking in load-bearing elements if not properly assessed
- Water ingress through active cracks in wet area or external-adjacent walls
- Ongoing crack widening if active movement is not addressed
- Cosmetic repair cost recurring if underlying cause is not resolved
- Purchaser and strata disclosure obligations where significant cracking is present
- Mould risk at crack locations in wet areas
- Impact on building valuation and marketability
Inspection Requirements
Download Inspection Checklist- Map all internal cracks recording width, length, orientation and location.
- Classify each crack using a standardised classification system.
- Install tell-tale gauges at active cracks and monitor over a minimum 4–6 week period.
- Assess whether cracking is in the plasterboard finish coat, the substrate or the structure behind.
- Check for associated movement — binding doors, gaps at junctions, deflecting floors.
- Inspect the exterior at the equivalent location to determine if facade cracking corresponds to internal cracking.
- Engage a structural engineer for any crack wider than 1 mm or showing signs of structural significance.
- Record all cracks with photographs and measurements before patch repairs obscure the evidence.
Start Inspection Checklist
Create a project inspection record, add defect locations, upload photos, and save notes for scope writing.
Typical Repair Methodology
- 01.Confirm whether cracks are dormant before proceeding with cosmetic repairs.
- 02.For dormant hairline plasterboard joint cracks — apply a flexible jointing compound, feather edges and re-coat.
- 03.For dormant fine to medium cracks in plaster — rake out to 6 mm depth, apply a flexible filler, feather and repaint.
- 04.For dormant cracks at wall-to-ceiling junctions — apply a flexible acrylic sealant rather than a rigid compound.
- 05.For active cracks — install tell-tales, monitor, identify cause and address root cause before any cosmetic repair.
- 06.For structural cracks — engage an engineer to specify the repair before any works proceed.
- 07.Where cracking is caused by absent control joints — install joints at the correct locations.
- 08.Sand and repaint all repaired areas using a compatible paint system matched to the existing.
- 09.Repaint walls and ceilings where patching produces an uneven finish across the visible surface.
Related Repair Systems
- Plasterboard joint and crack repair systems
- Flexible sealant crack repair systems
- Structural crack injection and assessment services
- Internal render and plaster repair systems
- Crack monitoring and tell-tale systems
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