Common types of render damage
| Problem | What it looks like | What it usually means |
|---|---|---|
| Hairline crazing | A fine web of surface cracks | Shrinkage as the render cured; often cosmetic |
| Single cracks | A line running from a window corner or along a joint | Movement, or a weak point in the wall |
| Hollow or blown render | Sounds dull when tapped; may bulge | The render has lost its bond with the wall |
| Damage at the base | Crumbling or missing render near the ground | Water and frost, often from bridging the damp-proof course |
| Cracks around sills | Splits below or beside a window | Water running off a sill that doesn't throw it clear |
| Staining | Dark streaks or damp patches | Water coming from a gutter, downpipe or sill above |
Finding hollow render
The simplest test is your knuckle. Sound render gives a solid knock. Render that's come away from the wall sounds dull and hollow. When we look at a wall, we tap our way across it to find out how far the hollow areas go, because what you can see is usually only part of it. A crack might be a metre long, but the render around it can have let go over a much bigger area.
How a render repair is done
- Mark out the damage. Hollow and cracked areas are mapped so we know exactly what's coming off.
- Cut back to sound render. The failed render is cut out to a clean, firm edge. Feathering new render onto old, loose edges is one of the main reasons patches fail.
- Prepare the wall. The exposed background is cleaned and checked, and any damaged brick or block is dealt with.
- Rebuild in coats. New render goes on in coats to the same thickness as the old, so the patch sits flush.
- Match the finish. The surface is worked to match the texture around it.
- Paint if needed. On painted render, the repair is painted, and often the whole elevation, so the colour is even.
Fix the cause, not just the crack
A render repair only lasts if whatever caused the damage has been dealt with. The usual suspects:
- Leaking gutters and downpipes running water down the face of the wall.
- Window sills that are too short, cracked or have no drip underneath.
- Render below the damp-proof course, drawing moisture up from the ground.
- Garden walls with no proper coping, letting water in from the top.
- Movement where an extension meets the house or two materials meet.
If the render is patched and the gutter above it keeps overflowing, the repair won't see out two winters. So we'll point out what we think is causing the problem, even if fixing it isn't our job.
When a crack is more than a render problem
Most cracks in render are just that. But wide cracks, cracks that run diagonally in a stepped pattern, or cracks that keep reopening after repair can point to movement in the wall itself. If we see signs like that, we'll tell you, and it may be worth asking a surveyor or structural engineer to look before any render goes back on.
Matching the repair
Painted sand and cement render is the easiest to repair. Once the patch has cured and the wall is painted, the repair largely disappears. Through-coloured renders like monocouche and silicone are harder. Even with the same product and colour, new render won't look exactly like render that's been weathering for years, so a patch can show. Sometimes repainting the whole elevation, or re-rendering a whole wall, gives a better result than a patch that stands out. We'll be honest about what to expect.
Older and historic render
Older houses may have lime render, and historic fronts in Brighton and Hove are often lime stucco. Patching those with a hard cement render creates a new problem: the cement is stiffer and less breathable than the lime around it, so the edges crack and moisture gets trapped. Repairs to lime render need to be in lime. See our page on stucco repair in Brighton and Hove.
Keeping render in good order
Render needs very little, but a check once a year pays for itself. Walk round the house and look for new cracks, especially around windows and at the base of walls. Check that gutters and downpipes aren't leaking. Make sure soil, paving and planters sit below the damp-proof course. Keep painted render painted before the old coat has broken down. And if a north-facing wall has gone green with algae, it can usually be cleaned gently; a high-pressure washer held too close can damage the surface.
Repair or re-render?
If the damage is limited and most of the render is sound, a repair is usually the sensible answer. If large parts of a wall sound hollow, or the render has been patched again and again, a new render is often better value. See our pages on rendering a whole house and rendering a single wall. If your walls are pebbledashed, see pebbledash repair and covering.
Frequently asked questions
Can you repair just one area of render?
Yes. Small areas of cracked or blown render can be cut out and repaired without touching the rest of the wall.
Will the repair match the rest of the wall?
On painted render, once it's repainted, usually yes. Through-coloured render is harder to match exactly, because older render has weathered. We'll tell you what to expect.
What causes render to crack?
Water getting in behind it, movement in the wall, a mix that was too strong, or render that dried too quickly when it was first applied.
Why does my render sound hollow?
It has lost its bond with the wall behind. Hollow render needs cutting back to sound edges and repairing.
Is it worth repairing old render?
If most of it is sound, yes. If large areas have failed, re-rendering is often better value.
Are your quotes free?
Yes. Send us photos of the damage and tell us roughly how big the area is, and we'll come back to you with a free quote.
Render needs fixing?
Send us a few photos of the damage, close up and from further back, and tell us roughly where it is on the house. We'll come back to you with a free quote. For all our exterior work, see our rendering services in Haywards Heath.
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