Who this guide is for
- Owners who have noticed cracking on a rendered or clad elevation
- Anyone preparing to describe a facade problem to a professional
- Renovators deciding whether a crack is cosmetic or structural in origin
- Readers who have been offered a repair with no diagnosis attached
- Anyone documenting an elevation before commissioning work
The principle: the pattern is about the layer beneath
Render forms an unbroken skin over the wall, which is what gives the smooth appearance and also means it has nowhere to relieve movement except by cracking. Beads and joints are the only places anyone decides what the facade does under stress; where they are omitted, movement and water still occur, but they choose their own locations.
A bonded facade behaves the same way for the same reason. With no cavity, background movement is transmitted rather than interrupted, so the movement joint grid is the assembly's only provision for it. The pattern that appears is therefore a map of where movement was not given somewhere to go.
A regular grid says board layout
Over a rendered external insulation build-up, the record names this directly: cracking along a regular grid is read as poor rendering, when the grid is usually the board layout showing through a base coat. The reinforcing mesh spreads local movement and impact across a wider area, so what would be a crack over a board joint becomes a distributed strain — but only where the mesh sits within the base coat rather than against the insulation or on the surface.
Buried too deep, the mesh leaves the outer face unreinforced and cracks appear over every board edge. So a regular grid is a question about the position of the mesh and about the layer behind the render, rather than about the finish coat itself.
A line following a frame member says the background changed
Where a render is worked across a panel and onto a structural member, it meets a different background, a different suction and a different movement pattern at every panel edge. The infill wall record states the consequence: carrying the coats straight across that change is what puts a crack on the line of the frame.
The direct render record generalises it. A wall of mixed materials, patched openings, old repairs and different mortars is several backgrounds behind one plane, and the render reads their boundaries back to the street as cracks along the changes.
Cracking at opening corners says a joint is missing
Openings are where the background changes most, from masonry to lintel to frame, and where movement concentrates. Where movement joints are omitted, the external insulation record notes, the difference appears wherever the build-up happens to be weakest, usually at an opening corner.
That is also where two movement provisions can compete. In an infill panel, an opening sits within an element that is itself moving relative to the frame around it, so where the opening head is close to the panel head, the window perimeter and the panel head are asking for the same space.
Horizontal cracking at a storey line says something about support
Two junction records describe horizontal cracking at a floor line and they describe different causes. Beneath a masonry support angle, a horizontal crack with spalled brick faces immediately under the support is the movement question: the joint under the angle was mortared solid, so the release the design relied on never happened and the weight above was handed back into the masonry below.
Under the soffit of a frame member above an infill panel, horizontal cracking with mortar squeezed out along the top of the panel says the panel has become a prop. The tell the vertical edges cannot give is openings within the panel going out of square, with doors and windows binding against heads that have come down onto them.
Uneven joints between units say tolerance ran out
On a precast facade the record reads uneven joints not as poor workmanship but as structural tolerance appearing where the fixing adjustment ran out. Because the joint is also the weathering element, that setting-out problem becomes a water problem as well as an appearance one.
On a rainscreen the same shortfall reads as tapering joint lines accumulating toward one end of the elevation rather than showing at the panel where the error started, while a single panel sitting proud or dropped with uneven joints around it points at that panel's own fixings instead.
- Tapering joints across a run: setting-out not recovered at the brackets
- One panel out of line: a fixing question at that panel
- Cracking at a panel's weakest section around an opening: restraint became support
- Cracked pointing and displaced slips at corners: differential movement with nowhere to go
A crack is not always a surface problem
On a bonded facade, a movement joint filled with grout is described as a line of units waiting to debond, and a failure anywhere in the chain of bonds presents identically from the outside, as units coming off. On a slip facade, movement gathers where the assembly is stiffest, at corners and around openings, and appears as cracked pointing before it appears as displaced facings.
The render record adds the reason not to cover any of it: a cracked render is worse than no render where water can enter and then cannot leave, because the coats now shelter a wetted wall from the drying it once had, and covering a consistent crack line without diagnosis leaves the cause in place.
Recording a facade crack before anyone repairs it
- 1Photograph the whole elevation, then the crack, so the pattern and its position are both visible
- 2Note whether the cracking forms a regular grid, follows a line, or concentrates at corners
- 3Note whether it coincides with a storey line, a panel edge or an opening
- 4Note whether joints between units are even along the run or taper toward one end
- 5Note whether one unit is proud, dropped or out of line with its neighbours
- 6Check whether a movement joint exists nearby and whether anything has filled it
- 7Note any spalled faces, squeezed mortar or displaced units adjacent to the crack
- 8Note whether doors or windows in the same area bind or have gone out of square
- 9Record whether the crack has been filled before and whether it has come back
- 10Record any staining, damp or efflorescence appearing internally at the same level
- 11Establish what the facade is made of before interpreting the pattern
- 12Take the record to a professional rather than making the repair first
Common mistakes to avoid
- Reading cracking as a failure of workmanship when it is the background reporting where it moves
- Treating a regular grid of cracks as a rendering fault rather than a board layout
- Filling a movement joint and expecting it to still be a movement joint
- Covering a consistent crack line without establishing what caused it
- Reading uneven joints between large units as poor workmanship
- Assuming a bonded facade with sound grout is soundly bonded
- Repairing a crack that keeps returning without recording that it has returned
When to involve a professional
- Ask what the facade is bonded or fixed to, and what that layer is in turn attached to
- Ask where the movement joints are and how far through the build-up each one reaches
- Ask whether any movement joint has been bridged by a later finish
- Ask a structural professional to distinguish settlement, thermal and moisture movement in an existing wall
- Ask whether cracking at a storey line relates to a support or a deflecting member above
- Ask what the smallest area is that could be made good without the repair being obvious
Frequently asked questions
Questions readers ask about this topic
Does a crack in a render mean the render was applied badly?
Not necessarily. The record describes cracking as often being the background telling the surface where it moves, and notes that a render is continuous while the wall beneath it is not. Openings, lintels, changes of material and structural joints are all candidate lines unless each is given a joint.
Why do cracks appear in a regular grid?
On a rendered external insulation facade, a regular grid is usually the insulation board layout showing through the base coat. Whether it appears depends largely on where the reinforcing mesh sits within that coat, because mesh buried too deep leaves the outer face unreinforced over every board edge.
Is cracking at the corner of a window normal?
It is common, and the records treat it as a report rather than as an inevitability. Opening corners are where the background changes most and where movement concentrates, so cracking there generally indicates that movement arrived at a point where no joint had been provided for it.
What does a horizontal crack at a floor line mean?
The junction records give two distinct causes: a masonry support angle whose movement joint beneath it was mortared solid, and an infill panel built tight to the soffit above so that it has become a prop. Both are structural questions and belong with the building's engineer rather than with a facade repair.
Should I just fill the crack?
The records advise against filling without diagnosis, because cracks that follow a consistent line are evidence about the construction behind and covering them leaves the cause in place. On a render, they also note that water entering a filled crack that cannot leave again is worse than the crack was.
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