The most important part of any landscaping project is the part you don’t see. We often get asked why quotes vary so much between contractors. The answer usually lies underground, in the depth and quality of the base preparation.

The Freeze-Thaw Threat

In Ontario, the ground freezes and expands significantly during winter. If your interlock is laid on a shallow base, or on soil that holds water like clay, the heaving ground will lift the stones, causing an uneven surface, tripping hazards, and pooling water. This is why cut-rate jobs often fail within two or three years.

Standard Excavation Depths

We adhere to (and often exceed) industry standards set by the Interlocking Concrete Pavement Institute:

  • Driveways: 12 to 18 inches, required to support vehicle weight and prevent tire ruts. On heavy clay soil, we dig deeper to ensure stability.
  • Patios and walkways: 8 to 10 inches, sufficient for pedestrian traffic, focusing on frost protection and drainage.

The Anatomy of a Base

  • Sub-grade: the native soil at the bottom of the excavation. We compact this before adding any stone to identify soft spots.
  • Geotextile fabric: a critical layer often skipped by budget contractors. This heavy-duty fabric separates the native soil from your new gravel base, so wet clay can’t mix in and weaken it over time.
  • Base material (Granular A): a mix of crushed stone and sand that packs tightly. We install this in two to three inch lifts, compacting each layer with a commercial vibratory plate tamper.
  • Bedding layer: a one-inch layer of limestone screening for the final leveling. This is what the pavers actually sit on.

Why Clay Soil Changes Everything

Much of our service area sits on heavy clay soil. Clay holds water like a sponge, and when that water freezes, it expands with tremendous force. On clay sites, we often recommend an additional sub-drain or extra gravel depth to buffer against this movement.

If you’re comparing quotes, always ask how deep a contractor is digging, and whether they’re using geotextile fabric. The longevity of your investment depends on those answers.