Old Canaan Building Materials

Stone dust is the fine byproduct of stone crushing — smaller and more uniform than crusher run, finer than sand in some gradations. It has specific, narrow correct uses: paver joint fill and a thin leveling layer under flagstone. It is frequently misused as a base material, where it compacts poorly and retains water in ways that cause exactly the frost heave problems a base is supposed to prevent.

Stone dust is grey, fine, almost powdery when dry, and pasty when wet. It compacts to a smooth, even surface in thin layers but does not drain the way coarser crushed stone does. In paver joints, it locks pavers together tightly and resists weed growth better than coarse sand.

Stone dust, also called stone screenings, is the fine particulate residue from crushing operations, typically passing a 1/4" or smaller screen. It is sold by the ton from quarries and stone yards, often as a low-cost byproduct. Correct uses: paver joint fill (swept into joints after laying), thin leveling course (1/2" to 1" maximum) under flagstone set on a compacted gravel base.

Stone dust retains moisture more than coarser aggregate and does not drain freely. Used as a structural base material — a common error — it compacts into an impermeable layer that holds water against the underside of pavers or stone, accelerating frost heave rather than preventing it.

Stone dust is correct only in thin layers and joint applications where its fine, compactable nature is the advantage. As a base material, crushed stone or crusher run is correct because it drains. Conflating the two — using stone dust as base — is one of the most common paving failures in New England.

From any stone yard or quarry, sold by the ton. Specify "stone dust" or "stone screenings" explicitly and clarify the intended use (joint fill versus leveling course) so the supplier provides the correct gradation.