Plastering & Rendering

Rendering help

Keith McKenzie 08/06/2026 - 8.01 AM

The render on our semi-detached house is failing in a few places. There are several fine cracks in the paint/render, blown out areas around windows and the render has come away where the old and new house parts join. There are no cracks or damp inside. Current render is sand/cement. ~40% of the external wall surface area is on the original 1930s house. I believe this is solid brick from previous DIY jobs. Remaining 60% surface area is on an extension from 2012 with cavity walls. From my research it seems lime-based render is typically recommended for solid walls, and silicone for EWI and cavity walls. I’d like to sense-check what I’ve seen on forums/Google with the real professionals! 1. Is silicone render OK on both wall types noting we have no internal damp issues from the sand/cement render? 2. Is there a different base coat that should be applied for silicone render to the solid walls? 3. Is there anything special to do for bridging old and new parts of the house to prevent future cracking? Thanks!

Mohammed

Rating: 5 out of 5

5/52 reviews

Edinburgh

Based on your description, the cracks around the junction between the old and new parts of the house are likely due to movement between the two structures rather than a render issue alone. Silicone render can work on both wall types when the correct base coat and reinforcing mesh system are used. The junction between the old and new sections would normally need special attention, such as reinforcement mesh and sometimes a movement joint, to help prevent future cracking. A site inspection would be needed to confirm the best system for your property.

Answered8 June 2026

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