In short
- Tap the wall: a hollow sound means render has lost its bond and will eventually come away.
- Hairline cracks are often cosmetic; wider, stepped or recurring cracks can signal movement that needs investigating first.
- Render that runs down over the damp-proof course to the ground is a common cause of damp and should be cut back.
- Patch repairs on through-coloured render rarely match perfectly; sometimes re-rendering an elevation is better value.
Common render faults we see on Surrey homes
- Hollow or blown render: render that has lost adhesion. It sounds dull when tapped and eventually falls.
- Cracking: from hairline crazing to wide cracks at window corners and along lintels.
- Bridged damp-proof course: render carried down to ground level lets moisture wick past the DPC.
- Failed beads: old galvanised beads rust, expand and push render off at corners and edges.
- Staining: algae and dirt streaks, often below sills without drips.
Diagnose first
A crack is a symptom. Before any repair, we establish why it happened: an over-strong render, drying shrinkage, thermal movement, a failed lintel, or movement in the structure. Cracks that are wider than a few millimetres, stepped, tapered, or that reopen after repair can indicate structural movement. That calls for a structural engineer or surveyor before rendering. See why render cracks.
Repair options
- Hairline crazing on sound render: clean and, on painted render, redecorate with a flexible masonry paint.
- Isolated cracks: cut out, fill with a compatible material and reinforce with mesh where needed.
- Hollow patches: cut back to sound edges, remove, and patch in layers that match the original system.
- Bridged DPC: cut the render back to a clean line above the DPC and fit a bellcast or base bead.
- Widespread failure: re-render the elevation or the whole house.
Matching an existing finish
Painted render is easy to match: repair, then repaint the whole elevation. Through-coloured render is harder. Colour depends on batch, weather and suction, so patches often show. If the repair is significant, finishing to a natural break such as a corner, or re-coating the elevation with a thin-coat system, gives a better result.
Questions people ask
Is a crack in my render serious?
Most hairline cracks are cosmetic. Wide, stepped, tapering or recurring cracks, or cracks that line up with cracks inside, need investigation before repair.
Can you repair just part of the render?
Yes. Hollow and cracked areas can be cut out and patched. Matching a through-coloured finish exactly is difficult, so plan repairs to finish at a corner or joint.
Why is my render coming away at the bottom?
Often because it bridges the damp-proof course and sits in wet ground, or because old steel beads have rusted. The fix is to cut back and fit a proper base bead.