Westminster Exposed Aggregate Concrete

Here's the thing about a washed finish: you can't fix it later. A heavy broom finish can be ground and recoated. An uneven trowel finish can be topped. But the stone in an aggregate slab either gets uncovered at the right moment or it doesn't, and the moment lasts as long as it lasts.

So this page is about pour day. Not stone samples, not sealer brands. The morning itself, because every decision that determines whether your walk looks like a river bottom or looks scrubbed happens between the truck arriving and the crew putting the hoses away.

The first half of the day, before anything gets washed

Forms are set and the base compacted before the truck is ever ordered, usually the day prior. Morning starts with a walk of the grade, a check that the steel is chaired and tied where it belongs, and a conversation about where the truck sits and how far the chute reaches. That last part sounds trivial. It isn't. On tight lots around Bradburn we've spent more of a morning solving access than placing concrete.

Then it arrives. Placed, raked to rough grade, screeded flat. Bull float next, which pulls a layer of paste to the top and buries the stone. That's supposed to happen. The rock you'll eventually see sits a fraction of an inch under a skin of cement and sand, and the rest of the day is about removing that skin at the right second without taking the rock along.

Surface retarder goes on while the slab is fresh. It keeps the top paste soft while the concrete underneath sets normally, which turns a frantic window into one a crew can work inside.

The wash itself

Testing starts with a garden hose and a soft brush at one corner. If stone rolls, we're early and we wait. If nothing moves under moderate pressure, we're late and the day just got harder. What we want is paste giving way while the aggregate stays locked, sitting proud but not loose.

Once that corner reads right, everybody moves. Brushes and controlled pressure, working in a line, holding the same depth of exposure the whole way across. Uniformity is the entire game. A slab washed deep at the house and shallow at the far edge looks like two pours joined in the middle, and there's no coming back from that.

A light acid rinse follows a day or two later, neutralized and flushed, to clear cement haze off the stone faces. Then it cures. Sealer waits weeks.

What moves the wash window on pour day

What a washed pour from us includes

• Excavation to firm material, soft pockets dug out instead of buried
• Road base compacted in lifts and graded to shed water away from the structure
• Number four bar chaired at a two-foot spacing, tied so it stays mid-slab
• Air-entrained mix ordered with your stone blend riding in it
• Surface retarder applied on schedule, not whenever somebody gets to it
• A crew sized to the square footage so the wash never pauses partway across
• Acid rinse, full neutralize, and a sealer date written down

Stone choice, and when we schedule these

The blend decides the look and it decides how the surface feels underfoot. Small rounded river rock gives a quiet texture that's easy on bare feet, which is why it lands around patios. Larger, more angular stone reads bolder from a distance and grips better on a slope. Darker blends hold July heat. Lighter blends show organic staining faster under trees.

Season runs late April to about mid-October, and September is our pick for this finish anywhere on the north metro. Winter is off the table for washing. The process ends with water sitting on a deliberately open surface, and no version of that works when it freezes overnight. We'll pour flatwork in January. We won't wash it.