Cracked render,
or something
underneath it?
A crack in render is a symptom, not a diagnosis. Patching it without knowing what moved is how a cheap repair becomes an expensive one. The pattern of the cracking usually tells you which you are dealing with.
The shape of a crack
tells you the cause.
Random hairline crazing across a render panel is usually shrinkage in the render itself. It is cosmetic, it is common, and on its own it does not mean the wall behind has moved.
A crack that is wider at one end than the other, runs diagonally, and steps through the wall is movement. That is a structural question and it needs monitoring or a structural engineer before anyone renders over it.
Horizontal cracks at regular intervals, typically every few courses and often on one exposed elevation, are the classic signature of wall tie failure. That regularity is the giveaway: the cracks are following the tie positions because the ties are corroding and expanding as they rust, jacking the courses apart. Nothing else produces evenly spaced horizontal cracking.
Render traps the water
it was meant to shed.
Sound render sheds water off the face of the wall. Cracked render does the opposite. Water runs into the crack, gets behind the render, and then cannot get back out because the render itself is not very permeable. It sits against the wall and it spreads sideways.
That is why the damp patch inside is almost never directly behind the crack. Water tracks down and across the back of the render and comes through somewhere else entirely, which is why people chase internal damp for years without finding it.
Tap the render. Where it sounds hollow it has already parted from the wall behind, and that area is holding water whether or not you can see a crack. Hollow render has to come off. Filling and painting over it seals the water in.
On a cavity wall, failed ties and cracked render often arrive together, because the same driving rain that got into the render is what corroded the ties.
Two different jobs,
two different scales.
Render repair is straightforward once the cause is settled. The failed area is cut back to sound material, the edges are keyed, and the patch is built up in coats and matched to the existing finish. Matching an aged render is the difficult part, and a patch that is technically correct can still look wrong, so on a prominent elevation it is sometimes better to take the whole panel back.
Wall tie replacement is a different order of work. The existing ties are located, new stainless steel ties are installed through the outer leaf into the inner leaf at the correct spacing, and the corroded ties are isolated so they cannot keep expanding. It is done from outside, and the holes are made good so they disappear into the wall.
The order matters. Replacing ties after rendering means drilling through your new render. If both are needed, ties first.
What your report
probably said.
Reports describe cracking carefully because surveyors cannot see inside the wall. Common phrasings include cracking noted to the render, hollow areas identified on tapping, and horizontal cracking at regular intervals consistent with wall tie failure, further investigation recommended.
The phrase further investigation recommended usually means a borescope inspection: a small hole is drilled and a camera looks into the cavity to confirm whether the ties have corroded before anyone commits to replacing them. That is a sensible step and it is far cheaper than assuming.
If the report mentions render repair around windows specifically, that tends to be a seal failure at the frame rather than a wall problem, and it is a much smaller job.
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Areas we cover.
We take render and wall tie repairs across all 32 London boroughs. Most of our work is in west London, in Shepherd's Bush, Hammersmith, Fulham, Kensington, Chiswick and White City, and in south west London, in Putney, Wandsworth and Wimbledon. We also work in south east London, in Greenwich, Blackheath and Lewisham.
If your property is outside these areas, call us anyway. We travel across London and will tell you honestly if a job is too far to price properly.