Exposed Aggregate

Exposed aggregate is concrete with the top layer of cement paste removed so the stones show. It is a finish on exterior flatwork, so the 2024 Ontario Building Code standard is the same: at least 32 MPa at 28 days and a water-to-cement ratio no higher than 0.45 (Div. B, 9.3.1.6. and 9.3.1.7.). For site-batched concrete the Code also says the aggregate must not be larger than one third of the slab thickness, and the mix needs 5 to 8% entrained air.

The Code's appendix warns that adding water on site can reduce strength and increase porosity and shrinkage cracking, which is worth asking about on any decorative pour. The National Research Council's winter digest notes that over-vibration and excessive trowelling hurt entrained air. Ask how the contractor exposes the stone and whether a sealer is part of the price.

Exposed aggregate costs more than a plain broom finish in the published prices we read. Ask for removal of an old slab, base work and any steps as their own lines on the quote. Since March 1, 2026 the City of Ottawa requires a hardscaping contractor licence for any business that installs or alters concrete pads, patios, walkways, steps, driveways or retaining walls on private property. Ask to see the licence and check the City's list of licensed hardscaping contractors yourself; we do not check it for you.