Reading the warning signs in cracked render.
Not every crack is a problem, and the ones that worry people least are often the ones that matter most. Here is how to read what your wall is telling you, and what each pattern actually costs to put right.
The pattern tells you more than the size.
People measure the length of a crack and worry about the long ones. Length is almost irrelevant. What matters is the pattern, the direction, the width, and whether it is growing.
As a rough field guide on width: under about 1 millimetre is usually a surface issue. Between 1 and 5 millimetres warrants investigating the cause. Over 5 millimetres, or wide enough to slip the edge of a 20 cent coin into, means get someone out and do not wait for the next season. Pencil a date beside a crack and check it in three months. A crack that has not moved is a different conversation from one that has grown 2 millimetres over a winter.
And use your knuckles. Tapping is the single most useful diagnostic in rendering and it costs nothing. Sound render rings solid and dull. Drummy render, meaning render that has lost its bond and is now a shell hanging on by its edges, sounds hollow, like a cardboard box. Tap the whole facade, low and high. Drummy patches decide whether you are re-coating or re-rendering, and that is a five-figure difference on a typical house.
What each type of crack means on a Bendigo wall.
Fine map crazing across a panel.
A network of very fine cracks, like crackle glaze on pottery, spread evenly across an area. This is a surface coating phenomenon: the top coat shrank slightly as it cured, usually because it went on in heat. Cosmetic. It is not letting meaningful water in and a flexible membrane texture coat will bridge it. Deal with it when you are due for a re-coat anyway.
Straight cracks running across the facade.
Ground movement, and in Bendigo that means reactive clay. Most of Greater Bendigo classifies M or H under AS 2870, the residential slabs and footings standard: the soil swells through a wet winter and shrinks through a dry summer, and your footings ride it. A rigid render laid across that movement with no control joints, or with joints that were never aligned to the building’s articulation joints, cracks along the line of stress. Filler does nothing here. The fix is cutting proper control joints and moving to a flexible system.
Diagonal cracks from window and door corners.
The corners of openings concentrate stress, so this is where movement shows first. A stair-stepping or diagonal crack running up and away from a window corner is the wall telling you it is flexing. Worth investigating properly, because occasionally it is footing movement rather than render movement, and that is an engineer’s question, not a renderer’s.
Bubbling, flaking or blowing at the base of the wall.
Confined to roughly the bottom metre, often with a white crystalline bloom on the surface. Rising damp or salt damp. Ground moisture is wicking up the wall carrying dissolved salts, and where it evaporates the salts crystallise and expand behind the render. On the gold-era solid brick around Eaglehawk and Golden Square there is frequently no damp-proof course at all. On newer homes it usually means the render was run past the DPC down to the soil, bridging it. Recoating achieves nothing. See salt damp render repair for what actually works.
Starred cracks radiating from a point.
Impact. Something hit the wall. A limb, a ladder, a cricket ball, a car. Localised and straightforward to repair, and unlike the others it is often an insurance job. Our render insurance guide covers how to document it so a claim actually gets paid.
What the diagnosis is worth.
A 2004 brick-veneer home in Kangaroo Flat, cement rendered, 140 square metres of wall. Two straight horizontal cracks about 3 millimetres wide running across the west elevation, fine crazing on the north wall, and a 1.5 square metre drummy patch below the kitchen window.
The cheap approach is a painter with a tub of flexible filler and a roller. Call it $3,400. Every one of those defects is back inside two years, because the horizontal cracks are clay movement that filler cannot restrain, and the drummy patch is going to let go regardless of what is painted on it.
The proper approach: cut and install two control joints on the west elevation aligned to the existing articulation joints, cut out and re-render the drummy 1.5 square metres, rake and fill the cracks with a flexible compound, wash and prime the whole facade, and apply a flexible membrane texture coat that will bridge the crazing. In 2026 that lands around $7,900 including scaffold. It is more than double the cheap option, and it is the last time that facade needs touching for 12 to 15 years.
The difference between the two quotes was not skill or price. It was ten minutes of tapping and reading the wall before anyone wrote a number down. The cost guide has the underlying rates, and how to choose a renderer covers how to tell which kind of quote you are being handed. Filling a crack is also the job people most often decide to tackle themselves, so it is worth reading DIY vs professional rendering before you buy the filler: on a movement crack the filler is the wasted part.
Render diagnosis across Greater Bendigo.
Cracked render questions.
Are cracks in render serious?
It depends entirely on the pattern, not the length. Fine map-like crazing across a whole panel is a surface coating issue and is cosmetic. A single straight crack running diagonally from the corner of a window or door is structural movement telegraphing through, and that one needs looking at. As a rough field guide, cracks under 1 millimetre wide are usually surface, 1 to 5 millimetres warrants investigation of the cause, and anything over 5 millimetres or wide enough to slip a 20 cent coin edge into means get someone out. Width, direction and whether it is growing tell you far more than length does.
What does drummy render mean?
Drummy means the render has lost its bond with the wall behind it and is now a shell hanging on by its edges. You find it by tapping the wall with your knuckles or a coin: sound render rings solid and dull, drummy render sounds hollow, like tapping a cardboard box. It matters because drummy render cannot be coated over. Any paint or texture you put on it comes off when the render eventually lets go, and in a Bendigo winter the freeze-thaw cycle accelerates that. Drummy sections have to be cut out and re-rendered.
Why is my render bubbling or flaking at the bottom of the wall?
Almost always rising damp or salt damp, particularly if it is confined to roughly the bottom metre and there is a white crystalline bloom on the surface. Ground moisture is wicking up the wall, carrying dissolved salts, and where it evaporates the salts crystallise and expand behind the render, pushing it off. On the gold-era solid-brick homes around Eaglehawk and Golden Square there is often no damp-proof course at all. On newer homes it usually means the render was run past the DPC down to the soil, bridging it. Recoating this achieves nothing. The moisture path has to be dealt with first.
Why has my render cracked in a straight line across the wall?
That is nearly always ground movement, and in Bendigo it is nearly always reactive clay. Most of Greater Bendigo classifies as an M or H site under AS 2870, the residential slabs and footings standard, meaning the soil swells through a wet winter and shrinks through a dry summer. Your footings ride that movement. A rigid render laid across it with no control joints, or with joints that were not aligned to the building’s articulation joints, cracks along the line of stress. The fix is not filler. It is cutting proper control joints and moving to a flexible system that can absorb the movement.
Can I just paint over cracked render?
Only for hairline crazing under about 0.3 millimetres, where a good flexible membrane coating will genuinely bridge it and hold. For anything else, painting over cracked render is the most expensive mistake in the trade, because you pay for the coating and you still have the problem, and now the problem is under a coating you have to strip. Every crack wider than hairline is a water entry point, and once water is in the render Bendigo’s sub-zero winter nights freeze it, expand it, and lever the render off the wall a fraction at a time. Fix the cause, then coat.
Not sure what your cracks are telling you?
Book a free measure. We tap the whole facade, read the crack patterns, find the cause, and quote the fix rather than the symptom.