Fort Collins Exposed Aggregate

Roll slowly down a block of older Fort Collins houses in late March and the washed-stone driveways sort themselves without any help. Some still read as rock. Others have gone flat and gray out at the street, or grown a bald stripe under the roof drip, or given up their whole shaded edge. You don't need to be in this trade to see it. Knowing whether you're looking at half an inch of surface trouble or a slab that's finished underneath, though, is the part worth getting right, because those two answers cost wildly different amounts.

Exposed aggregate is concrete with the cement paste washed back off the top so the rock carries the look and the traction. That top layer is thin on purpose, and it's also the only thing gripping the stone. Anything that eats paste shows up first as rock coming loose. Around here that means road chemicals, water with nowhere to go, and a lot of nights that cross freezing. The pattern of where the stone left tells us most of what we need before we open a truck door.

The four places a washed slab gives out first

Why the paste lets go, and what a repair honestly looks like

The wash is a timing job. Crews place, screed, and float like any other slab, then wait for the surface to stiffen to one specific point before hitting it with water and a broom. The other route is spraying a surface retarder early and washing hours later. Too soon and the rock rolls out and piles up at the low end. Too late and the paste has locked, so you scrub for an hour and get nothing. That window opens once, and wind and sun move it all day.

So the first question we ask about a failing slab is whether the paste was ever strong. An air-entrained mix washed at the right moment holds stone through decades of hard winters. A wet, over-tempered load washed an hour late does not, and no sealer fixes that. When the paste is sound and one zone is bare, we chip back to solid material, bond a topping in, and seed and wash stone into it. When the paste is soft across the whole slab, we say so, and the talk turns to replacement instead of a patch we'd both regret.

Picking stone that survives up here, and when we place it

Stone choice is the one decision on this job that you live with permanently, so we bring samples and set them out wet, since that's how they'll look every time it matters. Rounded river rock reads softer and feels better under bare feet. Crushed material grips harder and suits a sloped drive or a shaded walk. Darker stone hides the traction sand tracked around all winter; lighter stone stays cooler in July. Around Old Town, plenty of washed drives went in decades ago with whatever the plant had that week, and matching those exactly is a promise nobody should make.

Placement season runs from mid-May into the first half of October, and we're stricter at both ends than crews farther south would be. A washed slab spends its first hours wide open, and a hard overnight freeze in that condition is not recoverable. Fall is the best stretch: cool mornings stretch the wash window, the afternoon storms have quit, and the slab gets four weeks to cure before it meets a shovel. New pours in Registry Ridge and along the Harmony corridor go in on that schedule. Anything past mid-October waits for spring.