Guides / Why Concrete Cracks
Concrete cracks in Bendigo mainly because of three things: the big thermal swing from 40 degree summers to frosty winters, the reactive clay ground that swells and shrinks with the seasons, and localised settlement over old gold-mine workings in the older suburbs. All three are predictable, and a slab built to allow for them stays sound. The cracks you see around town are almost always the ones nobody built for.
A small amount of fine surface cracking is normal in any concrete and is not worth worrying about. The cracks that matter, the wide ones, the ones with a step across them, the ones that keep opening, come from stresses the slab was never designed to handle. In Bendigo those stresses are specific, so the prevention is specific too.
1. The thermal swing. Bendigo has a genuinely continental climate: hot dry summers that push past 40°C and cold winters with overnight frosts and sub-zero nights. Concrete expands in the heat and contracts in the cold, and a slab that swings through that range every year is under constant movement stress. Over a big area without room to move, that expansion and contraction has to go somewhere, and an unrelieved slab cracks. This is the stress people most often overlook, because it is invisible day to day.
2. Reactive clay shrink-swell. Much of the region sits on reactive clay and gravelly ironbark-forest soils that take up water and swell in the wet, then dry out and shrink back in summer. That ground literally lifts and drops under a slab through the year. A driveway or path that is not reinforced and jointed to ride that movement gets pulled apart from below, which is the classic Bendigo cause of a cracked, stepped slab.
3. Settlement over old mine workings. In the older northern suburbs, Long Gully, California Gully, Ironbark, Eaglehawk and Golden Square, there is the goldfields history underneath: shallow shafts, old workings and disturbed mullock fill. Where that fill was never assessed and compacted, it can settle unevenly under a rigid slab, and because concrete is stiff it cannot follow a soft spot, so it cracks over it. This is localised, block by block, which is exactly why the ground needs checking before a pour on the old diggings.
Every one of those causes has a known answer, and they are all set before or during the pour, not after.
All of this is why the ground and the build matter more than the finish. Concrete driveways in Bendigo walks through how the base, steel, joints and falls are put together for the block you are on. If you are laying a shed floor or a base for a build, the same principles apply and are covered on concrete slabs. And if you already have an older slab that is surface-worn but structurally sound, concrete resurfacing can refresh it, though a slab with wide moving cracks is usually a replacement rather than an overlay. If you want to know when to time a pour around the weather, the best time to pour guide covers the seasons.
Worried about an existing crack, or planning a new slab and want it built to last on your ground? Tell us your suburb and what you are seeing and we will get a local concreter out to look at it, no charge and no obligation. Call 0482 392 415 or use the contact page.
Bendigo puts three stresses on a slab that a milder, more stable location does not. The continental climate swings from 40 degree summers to frosty winters, so the concrete expands and contracts a lot. Much of the ground is reactive clay that swells when wet and shrinks when dry. And in the older northern suburbs there are old gold-mine workings and disturbed fill underneath that can settle unevenly. A slab built for those three things does not crack; one poured without allowing for them does.
Control joints do not stop concrete moving, they decide where it cracks. Concrete shrinks as it cures and expands and contracts with Bendigo's big temperature swings, and it will crack somewhere. Joints cut into the slab in a grid create weak lines that pull the crack down out of sight and let the slab move without tearing itself apart. Correct joint spacing is one of the main things that separates a tidy driveway from a cracked one.
No. Fresh concrete must not be allowed to freeze, because ice forming in the slab damages it permanently, and the cold slows the strength gain right down. A concreter will not pour into a frost and will protect a fresh pour from freezing overnight during the May to August cold. Pouring into frost is a common cause of a weak, crack-prone surface.
Not usually. Fine hairline surface cracks are normal shrinkage and rarely structural, especially if they follow or sit near control joints. What matters is wide cracks, cracks with a height difference across them, or cracks that keep opening, which can point to base or ground movement. If you are unsure, have a concreter look at it rather than guessing.
Get a free, no-obligation quote from a concreter who builds for the reactive clay, the thermal swing and the old diggings.