Why Is My Render Cracking? Causes and Fixes

Hairline cracks are common and often harmless, but cracks that widen, recur or let water in need investigating. Knowing the cause tells you whether a quick repair will do or the render needs replacing.

Common causes

• Movement in the building. Settlement or seasonal movement in the wall can open cracks along the same lines.

• Thermal movement. Walls expand and contract with temperature, which stresses rigid renders.

• Poor preparation. If the wall wasn't clean, sound and suitably prepared, the render may not bond.

• The wrong mix or system. An overly strong or unsuitable cement render can crack as it shrinks.

• Missing movement joints or beads. These are needed where different materials meet or on long runs.

• Water and frost. Water entering through a crack can freeze and expand, making damage worse.

• Impact and later alterations. Fixings, cables and building work can crack the surface.

How to tell how serious it is

What you see	Likely meaning	What to do
Fine hairline cracks	Surface shrinkage or minor movement	Monitor, and seal if needed
Cracks that follow window corners or joints	Stress at weak points	Have it inspected
Wide or growing cracks	Movement or failure	Get a survey
Hollow sound when tapped	Render has lost its bond	Get it assessed promptly
Damp inside near the crack	Water is getting in	Act quickly

Photograph and date any crack, and measure its width, to see whether it changes.

Repair options

• Sealing and recoating suits fine surface cracks, using flexible products compatible with your render.

• Cutting out and patching suits localised damage, but matching colour and texture takes skill.

• Re-rendering is the answer when large areas are hollow, damp or repeatedly cracking.

Preventing future cracks

Flexible, mesh-reinforced silicone systems cope with movement better than rigid renders. Good preparation, correct beads and movement joints, and repairing gutters and leaks matter just as much as the finish coat.

Getting it checked

Not sure which category your cracks fall into? Send close-up and wide photos to Alb Render on WhatsApp on 07846 928256 and we'll tell you what we'd do.

Related reading

• Can you render over existing render, brick or pebbledash?

• How to clean and maintain rendered walls

• What does a render warranty cover?

Explore our rendering services, see our recent work, or get a free quote.