Why Is My Render Cracking? Top Causes — And Why Silicone Render Is Often the Smarter Upgrade

Cracks appearing in your render can be frustrating — and a bit worrying.

Sometimes they’re cosmetic. Other times, they’re a sign the render simply isn’t suited to the building or the conditions here in the UK.

At Rains Plastering Ltd, we see this every week across Worcester Park and Surrey — and more often than not, the issue isn’t the house… it’s the render system.

In this guide, we’ll explain:

• why render cracks in the first place

• when it’s serious (and when it isn’t)

• why upgrading to silicone render is often the most reliable, long-term fix

We install EWI Pro silicone systems exclusively, and as approved installers, we know exactly how they perform compared with old sand-and-cement.

Are render cracks always serious?

Not necessarily.

Tiny, hairline cracks can happen as a house moves naturally.Wider, deeper or repeating cracks usually suggest a bigger issue.

The real danger is when cracks let water in. Once moisture gets behind render, you can start seeing:

• damp patches indoors

• blown or hollow render

• patches that keep needing repairs

So even small cracks are worth understanding.

1. Old sand and cement render that’s too rigid

What it looks like:Cracks around windows, corners and edges.

Why it happens:Traditional sand-and-cement render sets very hard. But homes expand and contract with heat, cold and daily movement. A rigid surface simply cannot flex — so it cracks.

Why silicone render performs better

Silicone render has built-in flexibility, meaning it can:

• absorb small movements

• resist hairline cracking

• protect the wall while still letting it breathe

In short: your house moves — silicone render moves with it.

Here in Surrey, with changing seasons, that makes a huge difference.

2. Poor preparation beneath the render

What it looks like:Cracks following weak patches, old paint lines or previous repairs.

Why it happens:Render only performs as well as the preparation underneath. If surfaces weren’t cleaned, primed or reinforced properly, it fails later.

How EWI Pro systems help

As approved installers, we use:

• specialist primers for strong adhesion

• reinforcing mesh to spread load and help prevent cracking

• a complete, tested system designed to work together

That means far fewer weak spots — and far less risk of cracking down the line.

3. Wrong product for the property

What it looks like: Random cracking, chalking, flaking finishes.

Why it happens: Older properties, solid walls and modern blockwork behave differently. Using the wrong render traps moisture or becomes brittle.

Why silicone render is usually the safer choice

Silicone render is:

• breathable (lets moisture escape)

• highly water-repellent (rain beads and runs off)

• coloured through (no repainting every few years)

• resistant to algae and staining

So instead of constantly patching, you get a finish that actually stays looking new.

4. Weather damage — frost, heat and heavy rain

What it looks like:Cracks appearing shortly after installation.

Why it happens:Rendering in bad weather stops it curing properly — and the problems show later.

The silicone advantage

High-quality silicone systems like EWI Pro are:

• UV resistant

• frost resistant

• durable against driving rain

And because installations are carefully planned around weather conditions, the finish has the best chance of lasting.

5. Damp and water ingress

What it looks like:Bubbling, staining and cracked areas beneath gutters and sills.

Why it happens:Water works its way behind the render. As it freezes or evaporates, it forces cracks open.

How silicone helps here

Silicone render is both:

• water-shedding on the surface

• breathable underneath

This is the ideal balance for damp-prone areas. Fix the leak, protect the wall, and future problems are far less likely.

So… is silicone render worth the investment?

For most homeowners we visit across Worcester Park and Surrey, the answer is yes.

While sand-and-cement may look cheaper on day one, silicone render often works out better value because it:

• resists cracking

• rarely needs repainting

• keeps its colour for many years

• is easier to clean

• reduces ongoing maintenance costs

  
  

When you factor in scaffolding, labour and repeated repairs, a proper silicone system usually pays for itself over time.

it is about choosing something built to last.

DIY repairs vs calling a professional

Small surface cracks can sometimes be sealed — but if the cause isn’t addressed, they will return.

As approved EWI Pro installers, we:

• diagnose the real reason cracking has happened

• check for damp and movement

• recommend the right long-term solution

• install a full, warrantied system — not just a patch

That is the difference between “fixed for now” and fixed properly.

Thinking about upgrading your render?

If your render is cracking, discoloured or constantly needing repairs, it may simply be time for something better.

We are local, experienced, and trusted across Worcester Park and Surrey — and we install EWI Pro silicone render exclusively, because we know it performs.

Rains Plastering Ltd Approved EWI Pro Installers Honest advice. Quality finishes. Built to last.

Get in touch for a friendly chat, a site visit, or a quote.