Façade & External Envelope

Render Cracking & Delamination

External render cracking and delamination is one of the most prevalent facade defects in Class 2 buildings. Render failures manifest as map cracking, shrinkage cracking, diagonal cracking at openings, and progressive loss of bond between the render layers or between the render and substrate. Delaminated render presents a falling hazard when at height, and allows water ingress behind the cladding layer — causing substrate deterioration, corrosion of embedded fixings and internal moisture damage. Early identification and containment are critical to preventing escalation.

Common Signs

Map cracking or crazing across render panel surfaces
Diagonal cracking at corners of windows and door openings
Hollow sound when render is tapped — indicating delamination
Visible separation and lifting of render at edges and junctions
Staining and moisture streaks below cracks or joints
Paint blistering and bubbling over render surfaces
Fallen render debris at the base of the building

Common Causes

Render applied too thick in a single coat without sufficient substrate key
Inadequate or absent movement joints allowing thermal and shrinkage stress
Incompatible render products applied over existing layers
Smooth concrete or masonry substrate without mechanical preparation
High water-cement ratio in the render mix causing excessive shrinkage
Render applied in hot, dry or windy conditions without curing protection
Substrate movement or deflection transferring stress to the render layer

Risk of Neglect

Delaminated render panels detaching from height — falling hazard to pedestrians below.
Water ingress behind render causing substrate deterioration and internal water damage.
Corrosion of embedded ties, fixings and reinforcement from moisture penetration.
Accelerating failure of adjacent sound render areas if delamination is not contained.
Significant cost escalation from a piecemeal repair approach versus early full remediation.
Staining and aesthetic impact on building appearance and property values.
Potential owner corporation liability for failure to maintain the building's external envelope.

Inspection Requirements

Map all visible render cracks across the facade, recording crack width, pattern and location relative to structural elements and movement joints.
Tap the render surface with a hammer over the full affected area — a hollow sound indicates delamination between the render and substrate.
Assess the extent of delaminated areas by hammer sounding and mark boundaries for quantification.
Inspect the original render composition and layer thicknesses by probing exposed or broken edges — excessive single-coat thickness is a common cause of failure.
Check the condition and position of control and movement joints — cracking at mid-panel locations often indicates absent or inadequate joints.
Assess substrate condition where render has already detached — check for moisture, contamination, smooth formwork faces or inadequate mechanical key.
Inspect flashings, window heads and horizontal ledges for water directing onto the render surface.
Engage a facade engineer or specialist contractor where delamination affects large areas or where the render is at height above pedestrians.

Start Inspection Checklist

Create a project inspection record, add defect locations, upload photos, and save notes for scope writing.

Typical Repair Methodology

Render repairs require full removal of all delaminated material, substrate preparation and a correctly specified two-coat render system. Spot repairs to delaminated render are generally not successful and result in recurring failure.

01.Erect scaffolding or swing stage to provide safe access to all affected facade areas.
02.Conduct a full hammer sounding survey of the facade and mark all delaminated areas — include buffer zones around mapped boundaries.
03.Remove all delaminated, cracked and hollow render by hand-held breakers or chisels to expose the sound substrate.
04.Clean the exposed substrate surface to remove all dust, contamination, paint, oils and old adhesive.
05.Check and prepare substrate surface profile — mechanically scabble or acid etch smooth masonry or concrete substrates to improve bond.
06.Install movement joints at maximum 4.5 m centres in each direction and at all structural junctions in accordance with AS 3700 and render manufacturer requirements.
07.Prime the prepared substrate with the specified render bonding agent and allow to tack before applying render.
08.Apply the first scratch coat of fibre-reinforced polymer-modified render to the primed substrate at 6–10 mm thickness and key the surface.
09.Allow the scratch coat to cure for a minimum of 7 days before applying the finish coat.
10.Apply the finish coat at 4–6 mm thickness, finishing to the specified texture and profile.
11.Seal all interface junctions between the new render and windows, doors, flashings and adjacent materials with a compatible polyurethane or silicone sealant.
12.Apply a breathable, UV-stable acrylic or elastomeric coating system to the completed render in accordance with the specification.
13.Record all QA documentation including photographs, area measurements, product batch numbers and moisture readings.

Related Repair Systems

Polymer-modified two-coat render systems
Fibre-reinforced render and mesh systems
Elastomeric facade coating systems
Movement joint and sealant systems
Facade bonding and priming systems

Open Repair Systems →