Safest Way to Clean an Exposed-Aggregate Patio

If your exposed-aggregate patio is turning green and slick, you’re right to hesitate before you “just pressure wash it.” With sealed aggregate, you can wreck the look quickly by treating it like bare concrete under a pressure washer. That is a bull in a china shop for sealer.

The safest approach for cleaning an exposed-aggregate patio is a controlled, step-up process: figure out what your sealer is doing first, then use a sealer-safe cleaner, give it dwell time, scrub lightly to break up the biofilm, and finish with a gentle rinse. Do it this way and you restore traction without creating patchiness or haze that forces a reseal.

Identify Your Sealer Risk

You can do everything “right” and still end up with cloudy patches or peeling if the patio is sealed differently than you assume. A 60-second check now is cheaper than a full reseal later.

Pick a dry spot and do a quick water-bead test before you clean. Drip a teaspoon of water on the surface and watch it for 60 seconds. If it beads up and sits on top, you’re likely dealing with a film-forming sealer (acrylic/urethane-style). If it darkens the concrete or soaks in, it behaves more like a penetrating sealer.

That one minute changes your whole approach. A film-forming sealer can turn cloudy or peel—what damages concrete sealer most often—if you hit it with strong bleach mixes or close-range pressure. If you do it anyway, you’re inviting the same problems the pros warn about. A penetrating sealer won’t “flake,” but you can still roughen the cement paste or loosen aggregate if you clean too aggressively. If your water beads, treat the patio like it has a delicate topcoat and aim to kill and remove the growth rather than blasting until it looks brand new.

A quick water-bead check is one of the easiest ways to tell whether you’re dealing with a film-forming acrylic sealer or a penetrating sealer before you clean. Read more in our article: Concrete Sealer

Safest Cleaning Method Step-by-Step

Start dry: sweep off grit and leaves so you don’t grind sand into the sealer. A little elbow grease goes a long way. Pre-wet the patio (and nearby plants) with a garden hose, then apply a pH neutral cleaner for sealed concrete and let it dwell 5–10 minutes, keeping it damp. Lightly scrub slick or shaded areas with a nylon deck brush to remove green algae from exposed aggregate; you’re loosening biofilm, not sanding the surface.

Rinse with the gentlest force that works: a wide 25° or 40° fan tip, about 12 inches back, in broad passes. Stay away from cracks and edges, and skip turbo/0° nozzles. If a stain “needs blasting,” it usually needs more dwell and a second cycle instead.

Pre-wetting and protecting nearby plants helps prevent cleaner runoff from spotting leaves or stressing landscaping during exterior cleaning. Read more in our article: Protect Landscaping Cleanup

Pressure Washing Without Stripping Sealer

A homeowner rinses a shaded corner a little slower to chase a dark patch, and the finish changes mid-pass from glossy to dull (exposed-aggregate cleaning guidance). The machine didn’t malfunction; the settings and technique did what they always do on a vulnerable sealer.

For pressure washing exposed aggregate patio safely, if you pressure-wash a sealed exposed-aggregate patio like it’s bare concrete, you can strip the sealer in a single slow pass. With a rental-aisle machine or harsh coastal conditions, that mistake can turn into a regret fast. Your goal is to rinse and lift what your cleaner already loosened, not to “erase” every dark spot with force.

Keeping pressure conservative and using the right fan tip is the fastest way to avoid etching or stripping sealer on concrete flatwork. Read more in our article: Pressure Washing Concrete Safe |