Last year, we checked out a house in Torquay. From the street, it looked perfect as it was less than ten years old, really eye-catching. But on the south side, big chunks of render had started breaking off. We spent a day looking around and it took us maybe an hour to figure out the problem. When render fails, it’s almost always for one of a handful of reasons. And most of those reasons are easy to avoid. In our experience of 15 years across the South West UK, here are the 4 most common render cracking causes we have seen and exactly how we fix them.
Key Takeaways
- Cement render on older walls just traps moisture. That leads to cracking, blown patches, and it chews up the brickwork underneath.
- Poor prep is the main reason. Dusty surfaces, wrong primer or skipping a mechanical key. This usually makes all the difference.
- When render touches the ground, it draws damp straight up the wall, like a sponge.
- Don’t ever ignore the small cracks. Water seeps in through them and then freezes and expands. His makes the render fall off.
Mistake 1: Using Cement Render on an Old House
Old houses, you can think pre-1950, that had solid walls were designed to breathe. Builders used lime mortar back then which let moisture escape naturally. If you cover that with modern waterproof cement render, you just trap all that moisture inside.
What happens next? The render cracks and falls off in chunks. Underneath, the bricks begin to rot away.
Here’s how we handle it: We always check the property before we start. If it’s an old solid-walled building, we go with lime render. Lime breathes, moves with the building and won’t lock in moisture.
Mistake 2: Skipping the Preparation
This should be obvious but honestly it’s still the main reason render jobs fail. Render needs something to grab onto. If the wall’s dusty, painted, greasy or just too smooth, the render won’t stick. It’ll just hang there until gravity wins and it lets go.
We’ve seen people apply render straight onto pebbledash, old paint, moss and even damp walls. The result is that within a few years you get big hollow patches and chunks of render crashing down.
Here’s what we do: We prep every single wall the right way. We pressure wash it, remove the bad mortar and then use the right primer, and making sure there’s a mechanical key for the render to grip. No shortcuts. This is where most failures start, and we simply don’t risk it.
Mistake 3: Render Touching the Ground
Render should never touch the ground. Seriously, just don’t do it. If it does, it soaks up moisture like a wick and pulls it straight up from the soil into your wall.
Then as soon as winter comes, that damp freezes and expands. That makes the render blow off from the bottom up. You’ll see chunks chip away at ground level.
Here’s what we do: we always install a drip bead, which is a plastic or metal strip, about 150mm above ground. This does not let the damp to creep up and lets water run off to protect the base of the render. If you skip this step, you will basically face a lot of problems later.
Mistake 5: Painting Over Render
Paint locks moisture in. If you slap paint over render, you trap water inside. The wall can’t breathe, so moisture builds up, freezes and that will eventually push the render right off.
Even beautiful, newly constructed rendered houses get ruined because someone painted a coat of masonry paint. The owner thought it’ll protect the walls but it actually ruined them.
Here’s how we handle it: we stick with breathable finishes. If you want color, we pick coloured render instead of paint. Or if paint is necessary, we only use breathable formulas that let moisture escape.
Frequently Asked Questions
How much does render repair cost?
For small cracks, you may have to pay around £20 to £35 per square meter. If the render has blown, it goes up to £45 to £70 per square meter. And if you need a full re-render, it may cost you like £90 to £150 per square meter.
Why is my render cracking?
It’s usually due to thermal movement. Your walls face extreme sunlight especially if they face south, so they tend to crack the most.
Can you render over old render?
Sometimes, sure. But if your old render’s blown or loose, it needs cutting out first. No shortcuts there.
What’s the best render for a South West home?
If you’ve got a modern place, silicone or acrylic render is the best. For older properties, you can also use lime render because it lets the building breathe.
Conclusion
A good render protects your house from our wild South West weather. If you get it wrong, you’ll end up with not just cracks but also damp, rot and some serious repair bills inside your home.
We’ve been rendering houses across the South West for 15 years. We know how bad it can get due to common render cracking causes. We also know how to make it last.
What makes the difference between render that fails and render that stands up to the weather? Know what you’re doing, get the prep right and pick the right materials for your building.
If you need your render checked and done properly, get in touch with Gamble Construction today. We’ll tell you what’s wrong, why it’s happening and how to fix it for good.
