Why exposed aggregate looks dirty so quickly
Exposed aggregate is concrete where the top layer of cement paste was washed away while curing, leaving the rounded stones on display. All those stones create a bumpy surface with deep little valleys between them. Dirt, tire dust, leaf bits and organic film settle into those valleys, where a broom and a hose never really reach.
The result is a driveway that slowly loses its contrast. The stones look dull, the paste between them goes gray or black, and the whole surface reads as one muddy color instead of a mix of tones. Shaded areas and spots under trees go first.
Many exposed aggregate driveways around Los Angeles are decades old. Age is not a problem in itself, but it means the surface has seen many seasons of dirt, sprinkler water and sun, and older surfaces need gentler handling than new ones.
The loose stone problem
The stones in exposed aggregate are held only partly by the surrounding cement. A narrow, high-pressure spray aimed at the gap between stones can undercut that cement and pop stones out. Once a few go, the surface gets pitted and more come loose with each cleaning.
Older driveways and those that were not sealed are more vulnerable, as are areas where cars turn. Before cleaning, walk the driveway and look for loose stones or bald patches. That tells you where to be gentle and sets realistic expectations.
If you do it yourself, the safest rule is simple: if you see stones moving or chips flying, stop and back off. Pressure that feels efficient on plain concrete is often too much here.
A safe method, step by step
Sweep or blow off loose debris first. Then pre-treat the whole surface with a concrete cleaner suited to what you see: a degreaser for oil and tire marks, a diluted chlorine-based cleaner for the gray and black organic film in shaded spots. Wet nearby plants before and after. Let the cleaner dwell long enough to break down the grime so pressure does not have to do the work.
Clean the open areas with a rotary surface cleaner at moderate pressure. Its spinning arms keep the nozzles at a fixed height and spread the force across a wide path, which is much kinder to the stones than a wand. Use a wand only for edges and corners, held at a low angle with a wide fan tip, never pointed straight into the gaps.
Rinse thoroughly from the high end of the driveway toward the low end. Keep the wash water out of the street gutter. Los Angeles Municipal Code section 64.70.02 prohibits discharging untreated wash water from paved-surface washing into the storm drain system.
Bringing back the contrast
Most of the color difference comes back once the film is gone from the valleys between stones. Let the driveway dry completely before judging, since wet aggregate always looks richer than dry.
If the surface still looks hazy after it dries, the cause is often efflorescence, a white mineral bloom common on concrete, or hard water spotting from sprinklers. Both need a specific mineral-dissolving cleaner rather than more pressure. Our existing guides on efflorescence and hard water stains cover those in detail.
Optional: sealing for a wet look
Exposed aggregate is one of the surfaces where sealing makes a visible difference. A film-forming sealer deepens the stone colors and gives a wet look, and it helps lock stones in place. The tradeoff is upkeep, since film sealers wear and need recoating. A penetrating sealer protects without much change in look.
Seal only after the driveway is fully dry. Moisture trapped under a coating turns it cloudy. Our guide on sealing concrete after pressure washing covers timing and product types.
When it needs repair, not cleaning
If large patches have lost their stones, cleaning will make the driveway clean but still patchy. Concrete contractors can resurface or patch exposed aggregate, though matching the stone mix exactly is hard. When we clean these driveways, our approach is to point out loose areas during the walkthrough so you know what is a cleaning result and what is the age of the slab.
Key points
The loose stone problem
The stones in exposed aggregate are held only partly by the surrounding cement. A narrow, high-pressure spray aimed at the gap between stones can undercut that cement and pop stones out. Once a few go, the surface gets pitted and more come loose with each cleaning.
A safe method, step by step
Sweep or blow off loose debris first. Then pre-treat the whole surface with a concrete cleaner suited to what you see: a degreaser for oil and tire marks, a diluted chlorine-based cleaner for the gray and black organic film in shaded spots. Wet nearby plants before and after. Let the cleaner dwell long enough to break down the grime so pressure does not have to do the work.