Can I use exposed-aggregate finish on my Ottawa driveway?

Yes, exposed-aggregate concrete is a viable and attractive option for Ottawa driveways — but it requires specific mix design and installation practices to survive the city's extreme freeze-thaw climate.

Exposed aggregate is created by placing a standard concrete slab and then washing or brushing away the surface paste before it fully cures, revealing the decorative stone aggregate beneath. The result is a textured, visually interesting surface with excellent traction — a real practical benefit on an Ottawa driveway that sees ice and snow for five months of the year. It is more durable than stamped concrete in Ottawa's climate because it has no surface pattern that can chip or scale at the edges, and the exposed aggregate texture naturally hides minor surface wear better than a smooth broom finish.

The Critical Mix Design Requirement

The single most important factor for exposed-aggregate concrete in Ottawa is air entrainment. Ottawa's 50-plus freeze-thaw cycles per winter will destroy non-air-entrained concrete within two to three years through a process called spalling — the surface flakes and pops off in sheets as water freezes and expands within the concrete's pore structure. Your concrete mix must contain 5 to 7 percent entrained air and a minimum compressive strength of 32 MPa (some contractors specify 35 MPa for exposed-aggregate work given the additional surface exposure). This is non-negotiable in Ottawa's climate. Any contractor who quotes you on exposed-aggregate concrete without specifying air-entrained mix design is cutting a corner that will cost you the entire driveway within a few winters.

The aggregate selection also matters. Rounded river stone aggregate (10mm to 20mm) is the most common choice and performs well. Crushed granite aggregate gives a sharper, more angular look but can be slightly harder on bare feet. Avoid limestone aggregate — it is softer and more susceptible to salt and acid attack, which is a real concern given Ottawa's heavy road salt use from November through April.

Base Preparation and Control Joints

Exposed-aggregate concrete driveways in Ottawa require the same deep base preparation as any other driveway surface. That means a minimum of 300mm compacted Granular B sub-base and 150mm compacted Granular A base — more if you are building on the clay soils common in Barrhaven, Orleans, Riverside South, or Gloucester. Skimping on base depth causes frost heaving that cracks the concrete slab regardless of how good the surface finish is.

Control joints must be cut every 3 metres in both directions to give the slab planned locations to crack as it expands and contracts. In exposed-aggregate work, these joints are typically saw-cut within 12 to 24 hours of placement and then sealed with a flexible polyurethane joint sealant. Unsealed control joints allow water infiltration and accelerate freeze-thaw damage at the joint edges.

Salt Damage and Sealing

Salt is the enemy of concrete driveways in Ottawa, and exposed-aggregate surfaces are more vulnerable than smooth concrete because the aggregate-paste interface creates micro-pathways for water and chloride penetration. A penetrating silane-siloxane sealer applied every two to three years dramatically reduces salt and water penetration and extends the surface life significantly. Avoid film-forming sealers on exposed aggregate — they trap moisture beneath the surface and can cause delamination. During the first winter after installation, use sand for traction only — no rock salt, calcium chloride, or any deicing chemical on new concrete until it has fully cured and been sealed.

Cost and Timing

Exposed-aggregate concrete driveways in Ottawa run $14 to $24 per square foot installed, putting an average 50-square-metre driveway in the $7,000 to $12,000 range. That is more than asphalt but less than premium interlock, and a properly built concrete driveway in Ottawa lasts 25 to 35 years with regular sealing and joint maintenance. Work must be done between late May and mid-September — concrete placed in cold conditions will not cure properly, and early frost exposure before adequate strength gain causes surface damage that cannot be repaired.

If you are ready to get quotes, Ottawa Driveways can match you with local concrete contractors through the Ottawa Construction Network — the matching service is free and there is no obligation.