Why Should We Use A Silicone Render? – Can I Just Ask? – Ep.9

When retrofitting solid wall buildings, especially those using external wood fibre insulation, choosing the right render is crucial. While traditional lime renders still have their place, they’re not always suited to modern performance demands. Silicone render offers a practical blend of breathability and weather protection that makes it well worth considering.

If you’d rather hear Andy and Chris talk through the ideas in this article, you can watch Episode 9 of Can I Just Ask? below. 👇

What is Silicone Render?

Silicone render is a modern, polymer-enhanced finish that typically comes as a pre-mixed, coloured paste. It contains silicone resins in a water-based solution, blended with fine aggregates and pigments. This paste is applied as a thin coat over a suitable base render, usually lime-based and reinforced with mesh.

The result is a flexible, crack-resistant outer layer that allows vapour to pass through while shedding rainwater extremely effectively. That combination of vapour permeability and water repellency is the key to its performance.

Where Lime Render Falls Short

For uninsulated solid wall buildings, a traditional lime render still does a good job. It allows the wall to breathe and offers decent weather protection in most cases. But once you add external insulation, particularly wood fibre, things change.

Wood fibre insulation turns the external wall surface into a much colder zone. Standard lime render can absorb large amounts of moisture during rainfall, and on a cold surface that moisture takes far longer to evaporate. This can lead to persistent dampness in the render and the outer layers of insulation, which over time will degrade the wood fibre itself.

In these conditions, lime render is simply too absorbent.

The Case for Silicone

Silicone render helps solve this problem. It allows internal moisture to escape through the wall but significantly reduces the amount of rainwater that can soak in from the outside. This keeps the insulation layer drier and protects it from long-term moisture damage.

In practical terms, that means:

• Less moisture retained in the building fabric
• Longer service life for the insulation and render system
• Reduced risk of freeze-thaw damage or biological growth

And with the UK facing increasingly wet and prolonged winters, limiting rain penetration is becoming even more important.

Useful Across Many Substrates

While it’s often discussed in the context of wood fibre insulation, silicone render is just as valuable on other substrates. Whether you’re working with traditional brick, stone or modern masonry, keeping external moisture out improves durability and internal moisture balance.

Even in projects where insulation is added internally, a water-repellent but breathable exterior render can help reduce the moisture load on the building fabric. This creates more flexibility for internal detailing and helps protect the overall integrity of the structure.

A Real-World Solution

It’s true that silicone renders include synthetic materials. But from a pragmatic perspective, they often offer the best balance of performance, protection and ease of use. While lime renders remain valuable in conservation and heritage contexts, they are not always the best tool for modern retrofit applications.

Silicone renders are not about cutting corners. They’re about selecting the right material for the job based on how buildings behave and what they need to perform well over time.