Why Does External Rendering Crack? Causes and Solutions
Cracks in external rendering (also known as external plaster or façade render) are a common issue that many homeowners and property managers face. Not only do they affect the aesthetic appeal of a building, but they can also indicate deeper structural or moisture-related problems. In this post, we’ll explore the main reasons why render cracks — and what can be done to prevent and fix the issue.
Main Causes of Cracks in External Render
1. Poor Surface Preparation
One of the most common causes of cracks is improper surface preparation before applying the render. If the substrate (such as brick or block) isn’t clean, stable, or dry, the render may not bond properly, leading to cracks over time.
2. Movement in the Building Structure
All buildings naturally move due to settling, thermal expansion, and contraction. If expansion joints are not correctly installed or the render isn’t flexible enough, even minor movement can cause visible cracks.
3. Using the Wrong Type of Render
Not all render types are suitable for all surfaces. For example, a rigid cement render applied on a flexible wooden or insulated wall may crack easily. Choosing the right render based on the wall type and environmental conditions is crucial.
4. Weather Conditions During Application
Applying render in extreme weather — too hot, too cold, or during heavy rain — can weaken the bonding process. Rapid drying or moisture intrusion can lead to surface cracking shortly after application.
5. Shrinkage Cracks
Some renders shrink as they dry. If the render is applied too thickly or allowed to dry too quickly, shrinkage cracks can appear.
Solutions and How to Prevent Render Cracks
✅ Use Flexible and High-Quality Materials
Opt for flexible render systems such as silicone or acrylic render, especially for buildings prone to movement or in areas with variable climates.
✅ Proper Surface Preparation
Ensure that the surface is stable, clean, and dry before rendering. Any loose material, dirt, or old paint should be removed.
✅ Apply in Suitable Weather Conditions
Plan rendering work during moderate weather. Avoid applying render during very hot, wet, or freezing conditions.
✅ Control Joints and Mesh Reinforcement
Install expansion joints where necessary and reinforce larger areas with mesh to prevent cracking caused by movement.
✅ Hire Experienced Professionals
Proper rendering requires skill and experience. A trained contractor will know how to assess the wall, choose the right materials, and apply the render correctly.