Stone Dust, Screenings, and Other Base Shortcuts Ontario Homeowners Should Refuse
If you look at interlocking failures across the GTA, you see the same pattern over and over. The pavers are usually fine. The problem is what they were sitting on. One of the biggest hidden reasons for early failure is the choice of cheap, inappropriate base or bedding materials, especially stone dust and limestone screenings.
Stone dust, often sold as limestone screenings or crusher dust, is a by product of crushing larger stone. It is very fine, with some small chips mixed in, and it is widely available and inexpensive. That combination makes it attractive to some contractors as a “base” or bedding material. The issue is not that it will not compact. It compacts extremely well, in the sense that it forms a very dense, almost impermeable layer. In Ontario’s climate, that is exactly the problem.
When stone dust sits under pavers in a freeze thaw environment, it tends to hold moisture rather than drain it. The layer becomes a kind of sponge. Water enters from above but leaves very slowly, if at all. When freezing temperatures hit, that trapped water expands and pushes upward, lifting the pavers. When it thaws, the material can slump. Over many cycles, that movement shows up as heaving, settling, and an increasingly uneven surface. Landscape contractors who have gone back to repair old installations built over screenings often find that the base is saturated and pumping when they step on it, with no clear path for water to escape.
Stone dust also breaks down under repeated stress. Those very fine particles can lose structure over time, especially when they are repeatedly soaked, frozen, and thawed. In heavy traffic areas, that means the layer that once felt rock solid can start to shift and deform. Some installers who used stone dust in the past now publicly advise against it because they have seen how it leads to pavers heaving and sinking after only a few winters, and how much extra labour is required to remove it when rebuilding a failed base.
On clay heavy GTA sites, stone dust can make a bad situation worse. Clay already holds water and swells when frozen. When you add a dense, moisture retentive stone dust layer on top, you set up a system where water and fine particles from the clay can migrate into the stone dust, further weakening the interface between base and subgrade. Instead of acting as a bridge between the pavers and the soil, that layer becomes a zone of movement and breakdown.
It is not just stone dust that causes trouble. Generic “recycled crush” or road base with unverified gradation can also create problems. Recycled aggregate can be used successfully when it is processed and graded to a clear specification, but when the mix of particle sizes, fines, and contaminants is inconsistent, compaction performance becomes unpredictable. A base built from inconsistent recycled material might compact well in one area and poorly in another. Those differences do not always show up immediately, but they emerge over time as uneven settlement and localized failures.
Another shortcut is skipping Granular B on truly poor clay subgrades that need it, and placing Granular A directly on the native clay without geotextile. Over time, clay fines can be pumped up into the base under load and moisture, slowly filling voids in the Granular A. That reduces drainage and load bearing capacity. The base that once behaved like a well graded aggregate begins to act more like a cemented mass of mixed clay and stone.
Even when the right materials are specified, the bedding layer can become a weakness if its depth is wrong. A bedding layer that is thicker than about 1.5 inches becomes unstable. Instead of acting as a thin cushioned interface, it can behave like a soft, shifting layer that allows pavers to move and settle. A screeded layer that varies in thickness across the project introduces micro variations that may not be obvious on installation day but become visible as bumps, dips, and rocking pavers over time.
For homeowners, the practical defense against these shortcuts is to require clarity in writing. A professional quote for interlocking in Ontario should specify:
Primary base material by name: Granular A, not just “gravel” or “base.”
Whether a Granular B sub base is included for driveways on clay or problem soil, and at what depth.
Bedding layer material by name: concrete sand or High Performance Bedding (HPB).
Depth of each layer before and after compaction.
If you see “stone dust,” “limestone screenings,” or “crusher dust” listed as the bedding or base material, you have your answer. If the quote only uses generic words like “screenings” or “base” without type and thickness, ask the contractor to specify. Contractors who understand how bases behave in Ontario’s climate will have no trouble answering these questions, and many will explain why they avoid stone dust and ungraded recycled material under pavers.
Choosing a contractor who uses Granular A as the primary base, Granular B where needed, and concrete sand or HPB as the bedding layer is not about being fussy over minor details. It is about making sure the money you spend on pavers is sitting on a foundation that matches our climate, our soils, and our traffic loads.
For a fuller breakdown of which base materials belong where, how they perform in Ontario conditions, and which shortcuts show up most often in failed installations, you can read the complete guide here: Interlocking Base Materials in Ontario: Granular A, HPB and More.










