How to Clean Exposed Aggregate Concrete

Exposed aggregate is one of the most popular finishes on the Fraser Coast — it looks great, hides marks well and handles our climate beautifully. But like any surface, it stays looking its best with a bit of regular care. The good news is that cleaning exposed aggregate is straightforward once you know the dos and don’ts. The bad news is that one common mistake — going too hard with a pressure washer — can do real, permanent damage.

This guide walks you through how to clean exposed aggregate safely, how to tackle the two problems we see most around Hervey Bay and Maryborough (mould and salt), and how resealing fits into the picture. Stick to these methods and your surface will keep looking sharp for years.

What makes exposed aggregate different

Exposed aggregate is concrete with the top layer of cement washed away to reveal the decorative stones underneath. That texture is what gives it grip and good looks — but it also means there are more nooks for dirt, mould and grime to settle into, and the exposed stones can be dislodged if you treat the surface too roughly.

The other thing to understand is the sealer. Most exposed aggregate is sealed, and that sealer is part of what protects the surface and brings out the colour of the stones. Aggressive cleaning strips the sealer, which is why technique matters so much.

The basic clean: regular maintenance

For routine cleaning, you do not need anything fancy. Done every few weeks or as needed, this keeps the surface from ever getting badly dirty:

1. Sweep first. Remove leaves, dirt and grit with a stiff broom. Leaf tannins can stain if left sitting, so don’t let piles of leaves linger.
2. Hose it down. A good rinse shifts most loose dirt and, importantly, washes off salt that builds up in our coastal air.
3. Use a mild cleaner for grime. For general dirtiness, a concrete-safe or pH-neutral cleaner with water and a soft-bristle broom does the job.
4. Rinse thoroughly. Don’t let cleaner dry on the surface — wash it all off.

That simple routine, done regularly, prevents most of the build-up that leads to bigger problems.

Pressure washing: the dos and don’ts

A pressure washer can be a great tool for exposed aggregate — or a destructive one. The difference is all in how you use it.

Do:

• Use a low-to-moderate pressure setting, not the maximum.
• Use a wide fan nozzle (e.g. a 25–40 degree tip), never a narrow pinpoint jet.
• Hold the wand well back from the surface — keep your distance and let the water do the work.
• Keep the spray moving in even, overlapping passes.
• Work at a consistent angle rather than digging into the surface.

Don’t:

• Don’t use a turbo/pinpoint nozzle — it concentrates pressure and can blast stones loose.
• Don’t hold the nozzle close to the surface.
• Don’t dwell in one spot.
• Don’t pressure wash freshly sealed concrete before the sealer has fully cured.

The damage from over-aggressive pressure washing is permanent: dislodged stones, eroded matrix and a stripped sealer that then leaves the surface open to staining. When in doubt, go gentler. A soft brush and cleaner will get you most of the way without any risk.

Removing mould and algae

Our humid, high-rainfall climate is a paradise for mould and algae, especially on shaded or poorly drained sections of exposed aggregate. You will often see it as green, grey or black patches.

To deal with it:

1. Sweep and rinse the area first.
2. Apply an appropriate mould and algae treatment suitable for concrete (follow the product directions carefully).
3. Give it the recommended dwell time, then gently scrub with a soft broom.
4. Rinse thoroughly.
5. Improve drainage or trim back overhanging plants if mould keeps returning to the same spot — fixing the cause beats repeat cleaning.

Avoid harsh, unsuitable chemicals that can damage the sealer or the surface. If mould is widespread or keeps coming back, it is worth getting it dealt with properly along with a reseal.

Removing salt stains and efflorescence

Living near the coast, you will likely deal with salt at some point. There are two related issues:

• Salt build-up from sea air, which a regular hose-down keeps under control.
• Efflorescence — a white, powdery or crusty deposit that appears when salts within the concrete migrate to the surface as moisture moves through it.

For light efflorescence, dry brushing and rinsing often lifts it. For more stubborn deposits, a specialist efflorescence remover may be needed — and these are typically mild acids, so they must be used carefully, exactly per the instructions, and rinsed off well. Persistent efflorescence usually points to a moisture issue (drainage or an unsealed surface drawing water through), so addressing that — and resealing — is the longer-term fix.

Removing common stains

Stain	Approach
Oil / grease	Absorb fresh spills, then use a degreaser made for concrete
Leaf / tannin	Clean promptly; don’t let leaves sit and stain
Rust	A concrete-safe rust remover; avoid harsh acids that pit the surface
BBQ / food	Mild cleaner and a soft brush
Tyre marks	Concrete-safe cleaner; agitate gently

Whatever the stain, the rule is the same: start with the gentlest method, test in an inconspicuous spot, and rinse thoroughly. Avoid throwing strong acids at the problem — they can strip sealer and etch the surface.

Resealing: the step that protects all your work

Cleaning and sealing go hand in hand. The sealer is what keeps stains, salt and moisture out in the first place — so once it wears off, the surface gets dirtier and harder to clean, which is the cycle you want to avoid.

A good rhythm is:

1. Keep up regular light cleaning.
2. When the surface starts looking dull, water stops beading, or staining gets easier — it is time to reseal.
3. Clean thoroughly and let the surface dry completely before sealing.
4. Apply a quality sealer suited to exposed aggregate in a coastal climate.

In our environment, exposed aggregate typically needs resealing roughly every 2–3 years. We cover the full picture in our concrete sealing guide, including sealer types and timing.

Common questions

Can I use bleach on exposed aggregate? Some diluted treatments are used for mould, but harsh, undiluted bleach can damage the sealer and surrounding plants. Use a product designed for concrete and follow the directions — and rinse well.

How often should I clean it? A quick sweep and hose as needed, plus a more thorough clean a couple of times a year, keeps most Fraser Coast exposed aggregate looking great. Coastal and shaded areas may need a bit more attention.

My exposed aggregate looks dull — is it dirty or worn? Often it is the sealer wearing off rather than the surface being dirty. A clean and reseal usually brings the colour and sheen right back.

Stones are coming loose — what happened? This is usually a sign of over-aggressive pressure washing or an ageing surface. Stop the harsh cleaning, and have it assessed — minor areas can often be addressed, and resealing helps protect what’s there.

A simple year-round care routine

The easiest way to keep exposed aggregate looking great is to stay ahead of dirt rather than waiting for it to build up. A light routine spread across the year takes very little effort and avoids the big, hard cleans altogether.

• Weekly to monthly: sweep off leaves and grit, and give it a quick hose down — this also washes away the salt that settles out of our coastal air.
• As needed: clean up oil, food or other spills promptly before they have a chance to penetrate.
• A couple of times a year: a more thorough clean with a concrete-safe cleaner and a soft broom, paying attention to shaded areas where mould likes to start.
• Every 2–3 years (coastal QLD): assess the sealer and reseal when water stops beading or the surface looks dull.

That is genuinely all most Fraser Coast exposed aggregate needs. The texture that gives the finish its grip and good looks is also what hides everyday marks, so a little regular care goes a long way.

Why gentle wins every time

If there is one message to take from this guide, it is that exposed aggregate rewards a gentle approach and punishes a harsh one. The instinct when a surface looks dirty is to reach for the most powerful tool and the strongest chemical — and on exposed aggregate, that instinct causes the very damage you are trying to avoid.

Loose stones, an eroded surface and a stripped sealer all come from going too hard. None of them are easy or cheap to fix. By contrast, a soft brush, a concrete-safe cleaner, a careful hand with the pressure washer and a reseal on time will keep the surface looking sharp for many years with no risk at all.

Start gentle, test in a hidden spot, rinse thoroughly, and seal on schedule. Do that and your exposed aggregate will stay one of the best-looking surfaces on the property.

Keep your exposed aggregate looking its best

Exposed aggregate is a low-maintenance finish when it is cleaned the right way and resealed on time. Treat it gently, stay on top of mould and salt, and it will reward you with years of great looks.

We install and maintain exposed aggregate across Hervey Bay, Maryborough, Rainbow Beach and Tin Can Bay, and we handle concrete sealing to keep it protected. If your exposed aggregate needs a proper clean and reseal — or you would like advice on caring for a new surface — get in touch for a written quote.