Cracks in concrete driveways are almost universal in Port Stephens — the coastal climate’s salt air, UV cycling and thermal expansion take their toll, and older driveways nearly always show cracking of some kind. The question isn’t usually whether a driveway has cracks; it’s what type of cracks they are and what to do about them.
Not all cracks are equal. Some are purely surface-level and can be filled and resurfaced over without any structural concern. Others indicate that something is happening in or below the slab that needs addressing before any surface treatment will hold.
This guide explains how to tell the difference.
Types of Cracks in Port Stephens Driveways
Hairline Cracks
What they look like: Very fine lines, typically less than 1mm wide, visible on the surface. Often spider-web (map) patterns across a section of driveway or in a connected network following tension directions.
What causes them: Concrete shrinks as it cures — hairline cracks often appear within the first year of a slab’s life from this curing shrinkage. They can also develop over time from thermal cycling (expanding in the sun, contracting at night), surface-level salt crystallisation, and minor drying of the subgrade.
Are they structural? Generally no. Hairline cracks on an otherwise sound slab are a surface condition, not a structural problem.
Can they be resurfaced? Yes. Hairline cracks are filled with flexible crack filler as part of the preparation process, then the overlay is applied over the top. The filled crack doesn’t reopen unless the slab is still actively moving.
Settlement Cracks
What they look like: Wider than hairline (typically 2–5mm), running in relatively straight lines across sections of the driveway. May or may not have minor vertical displacement (one side slightly higher than the other).
What causes them: Minor settling or movement of the slab or subgrade. All concrete slabs settle slightly over time — this is normal. Tree roots below the slab can also cause settlement cracks as roots grow and lift sections, or as roots die and the support they provided collapses.
Are they structural? Depends on displacement. Settlement cracks with no vertical displacement (both sides at the same level) are typically manageable with crack filling and resurfacing. Settlement cracks with significant vertical displacement (more than 3–4mm) indicate active movement in the slab that warrants further assessment.
Can they be resurfaced? Usually yes for cracks without significant displacement. For cracks with displacement, we need to assess whether the movement is ongoing or has settled. An ongoing active crack in a resurfaced surface will re-appear in the overlay.
Structural Cracks
What they look like: Wide (5mm+), often with clearly visible stepped displacement (one side noticeably higher than the other), may run diagonally across the slab.
What causes them: Significant ground movement — usually from poor compaction of the subgrade before the slab was poured, washout of subgrade fill material (common near drainage areas or in areas with poor stormwater management), or major tree root intrusion. Occasionally from vehicle loading beyond the slab’s design capacity.
Are they structural? Yes. Significant displacement means the two sides of the slab are at different heights — they’ve moved independently. This indicates either ongoing movement or past movement that has since stabilised.
Can they be resurfaced? If the movement has ceased (the crack hasn’t grown or changed in a year of observation), resurfacing may be possible with proper crack preparation. If movement is ongoing, no surface treatment will hold — the underlying problem needs to be addressed.
Map Cracking (Alkali-Silica Reaction)
What they look like: A dense network of cracks covering a wide area in a random pattern, sometimes with surface popping or lifting along crack edges. The whole surface looks like a cracked dry lake bed.
What causes them: In some cases, alkali-silica reaction (ASR) — a chemical reaction between certain aggregate types in the concrete and the alkaline cement paste. Salt contamination can accelerate or contribute to this in coastal environments.
Are they structural? Can be. ASR-affected concrete continues to expand and crack. Resurfacing over an ASR-affected slab is ineffective — the ongoing movement will crack any overlay.
What to do? If you suspect ASR (the cracking pattern is widespread and seems to be progressing), get the slab assessed by a specialist before committing to any surface treatment.
How Salt Air Contributes to Cracking
In Port Stephens’s coastal environment, salt plays a specific role in driveway cracking.
Salt crystals in concrete pores expand when they absorb moisture and contract when they dry. The repeated cycling of this expansion and contraction — known as salt crystallisation pressure — gradually widens existing micro-cracks and can initiate new ones. It doesn’t cause the dramatic displacement of structural cracking, but it accelerates the widening of surface and hairline cracks that are inherent in most concrete.
Close to the water — within 500m of the harbour or ocean — this process is more rapid because salt loading is higher. Driveways in these areas tend to show visible cracking earlier than those further inland.
The best response to salt-accelerated cracking: don’t leave surface cracks unfilled and unsealed. Salt entering through an open crack continues the process below the surface. Proper crack filling and resealing or resurfacing stops the ingress cycle.
The Preparation Process for Cracked Driveways
When we resurface a cracked driveway, crack preparation is a defined step:
Step 1: Assessment — We categorise every visible crack: hairline (fill direct), minor settlement (fill and feather), significant (assess displacement and recommend accordingly).
Step 2: Crack routing — For cracks wider than about 2mm, we run a crack router along the line to create a clean, V-shaped channel. This provides more surface area for the filler to bond to.
Step 3: Crack filling — A flexible polyurethane or epoxy crack filler is applied into the routed crack. We use flexible fillers rather than rigid ones — flexible fillers accommodate the very minor thermal movement that all concrete slabs have without re-cracking. Rigid fillers can break the bond with the slab under movement.
Step 4: Feathering — The filled crack is feathered smooth so the overlay goes over a consistent surface.
Step 5: Overlay — Once the filler is cured, the surface is primed and the overlay applied over the entire driveway including the filled cracks.
The end result: a smooth overlay surface with no visible cracks, over filled cracks that won’t reopen from normal thermal cycling.
Driveway Cracks and the Age of Port Stephens Homes
Many Port Stephens homes have driveways that are 20–40 years old. At that age, cracking of some kind is essentially universal. The questions are always:
- Is the cracking surface-only or structural?
- Is there any displacement?
- Is the cracking still progressing or has it stabilised?
We assess these questions every time. Our honest recommendation: if the cracks are surface-level or minor settlement with no displacement, resurfacing is appropriate. If there’s significant displacement or evidence of ongoing movement, we’ll say so rather than put an overlay over a problem that won’t be fixed.
Frequently Asked Questions
My driveway has a crack that’s been there for years and hasn’t changed. Is that a good sign? Generally yes. A crack that hasn’t grown or changed in multiple years indicates the movement that caused it has stabilised. Stable cracks can usually be filled and resurfaced over successfully.
There’s grass and weeds growing in my driveway cracks. What does that mean? Weeds in cracks mean the cracks are open and have been collecting soil over time. The cracks need to be cleaned out (weed killer, root removal, cleaning the channel) before crack filler goes in, otherwise you’re filling over a root system that will continue growing underneath. We handle this as part of prep.
My driveway feels solid when I walk on it but one section is about 20mm higher than the rest. What happened? Likely a tree root lifting that section from below. If the root is still there and growing, the section will continue to rise. This needs assessment — sometimes the section needs to be broken up, the root dealt with, and re-poured. An overlay won’t solve an actively rising section.
Can resurfacing fill cracks so they’re completely invisible? For hairline cracks filled and resurfaced over, the result is typically very hard to detect. For wider cracks that have been filled, the fill line is generally not visible under the overlay. For the widest cracks (5mm+), there may be a slight visual shadow where the crack was filled, though the surface will be smooth to touch.
I’ve been told to use flex seal or similar products on my cracked driveway. Will that work? Consumer-grade flexible sealants are a temporary measure at best. They don’t address the root cause, they don’t provide the bonding surface that a proper crack filler provides, and they can actually interfere with adhesion when a proper resurfacing job is later attempted. Use a proper crack filler product, properly installed.