Guide
Why is my render cracking?
Render cracks are usually caused by a mix that's too strong for the wall, water getting in at details, missing or corroded beads, movement in the building, or render applied in poor weather. Fine surface crazing is often cosmetic; wider, stepped or bulging cracks need investigating before repair.
Types of crack
- Crazing — fine map-like cracks in the surface, often from fast drying.
- Straight cracks at openings — from stress at window corners without reinforcement.
- Stepped cracks — following mortar joints, which may indicate movement.
- Hollow or bulging render — the render has lost its bond.
Repair or re-render?
Isolated cracks and small hollow areas can be repaired. If a large proportion of an elevation is hollow or cracked, re-rendering is often better value — and in England and Wales, re-rendering more than half of a wall brings in Building Regulations.
Preventing cracks
Mesh-reinforced base coats, beads at corners and edges, movement joints and suitable weather all reduce cracking.
Questions
Is cracked render dangerous?
Loose render can fall, so hollow areas at height should be checked promptly.
Can I fill cracks with sealant?
It may stop water briefly but rarely lasts and can look worse.
Why does new render crack?
Usually from mix, weather or missing reinforcement at stress points.