Pond Fines

Pond fines are the fine stone dust and mud that settles at the bottom of a quarry's wash ponds. When crushed stone gets rinsed to clean the dust off the rock, those tiny particles drain into a settling pond and build up as a thick, muddy slurry. Most of the material is silt-sized. About 80% or more of the grains pass a No. 200 sieve, so most of it is finer than table salt.

The name tells you where it comes from. Fresh pond fines are dredged out at 70 to 80 percent water, so the quarry has to dry them out before a truck can haul them anywhere. Once they're dewatered to around 20 to 30 percent moisture, they pack tight and shed water instead of soaking it up. That's why you'll see them used for pond and dam liners, flowable fill, or cheap sub-grade under driveways and yards. They're usually one of the least expensive loads a quarry sells, since it's leftover from washing the other rock.