Fix exposed aggregate concrete: Perth guide

Exposed aggregate looks tough, but it's actually three things working together — the concrete slab itself, the embedded stones, and the sealer holding the surface together. When the surface looks bad, only one of those is usually the real problem.

Before we quote any repair, we walk the slab and identify which layer is failing:

• Sealer failure — chalky-looking patches, water no longer beads on the surface, dull tone. Easy fix.
• Loose stones — small pebbles popping out underfoot, gritty surface. Usually a sealer-failure symptom.
• Hairline cracks (< 2mm) — cosmetic only, surface-deep. Easy fix.
• Wider cracks (> 2mm) — structural movement. Need investigation.
• Sub-base failure — slab tilted, large displaced sections, repeated cracking. Hard fix.

90% of what we see in Perth driveways is the first three categories — and the first three are cheap fixes done in a day.

Concrete cracks. It cracks during the cure (thermal shrinkage), it cracks under load (vehicle weight), and it cracks with seasonal temperature swings. Perth's 20°C+ day-to-night swings in summer + the dry winter air work the slab harder than most.

The good news: any hairline crack under 2mm is purely cosmetic. The slab is intact underneath. The fix is:

1. Clean the crack with a wire brush and blow out dust
2. Apply a flexible concrete crack filler (Sika or similar) with a caulking gun
3. Smooth with a wet finger and let cure 24 hours
4. Re-seal the patched area to blend it visually

We charge $300-450 for a half-day visit covering up to 10 hairline cracks plus a re-seal of the affected area. Most homeowners can do this themselves — the only catch is matching the sealer sheen.

When pebbles start popping out, the instinct is to think the surface has failed. It hasn't — the sealer has. Exposed aggregate relies on the sealer to lock the stones into the cement matrix. Once the sealer ages out (typically 5-7 years for outdoor driveways), the stones at the surface lose their grip.

The fix is straightforward:

1. Pressure wash the surface to remove dust and any remaining old sealer
2. Allow 24-48 hours to fully dry
3. Apply a penetrating sealer specifically rated for exposed aggregate
4. For severely loose stones, push them back into wet sealer and weight gently for 12 hours
5. Apply a top-coat sealer 7 days later

What we use: Marine-grade penetrating sealer for coastal Perth jobs (Scarborough, Trigg, Cottesloe), standard outdoor sealer for inland zones. The salt air degrades sealers faster — we recommend a 3-year reseal cadence near the coast vs 5-year inland.

Sun-faded exposed aggregate is a real problem in Perth — 12 months of summer UV plus salt air can dull a vibrant honey pebble or terracotta to a tired grey. The good news: the colour underneath the surface hasn't actually changed. It's a thin top layer that's sun-bleached.

Three options, cheapest to most thorough:

1. Tinted re-seal — a sealer with a pigment tone added that restores the visual colour. Best for slight fade.
2. Acid wash + re-seal — light acid etching strips the top 0.5mm of cement to expose fresh stone, then re-seal. Best for moderate fade.
3. Surface grind + reseal — diamond-grinder takes the surface back further. Reveals the deeper aggregate. Best for severe fade.

Acid wash is the most common we do — visible improvement in a single day, costs 10-15% of a full re-pour.

If you see cracks wider than 3-4mm, especially cracks that step (one side of the crack sits higher than the other), the slab is moving. That means the sub-base is the culprit, not the concrete.

Sub-base failure in Perth has two main causes — sandy soil settling under load (coastal suburbs) or clay shrink-swell in winter wet / summer dry (inland zones like Gingin and the foothills).

The honest call from us: there's no easy fix for sub-base failure. Patching the crack just creates a new crack 50mm away. The sub-base needs to be re-prepped, which means lifting the slab — at which point a re-pour is the rational choice.

The case for a full re-pour comes down to four signals:

1. Multiple wide cracks across the slab (more than 5-6 over the surface area)
2. Visible settlement — the slab sits unevenly compared to the kerb or path
3. Slab age past 25-30 years and showing cumulative damage
4. You want to change the finish (e.g. exposed to honed) — re-finishing is usually re-pouring

When it's clearly the right call we'll say so. The on-site quote is free either way — the goal is to give you a straight answer about what your slab actually needs, not the most expensive fix.