How long does new concrete take to cure in Ottawa?

The 2024 Ontario Building Code requires that when the air temperature is below 5 °C, freshly placed concrete be kept at not less than 10 °C for 72 hours after placing. Beyond that protection window, the Code measures concrete strength at 28 days, which is a strength benchmark, not a declaration that curing is complete.

For practical guidance on when to use a new slab, the Ready Mixed Concrete Association of Ontario advises keeping vehicles off freshly placed concrete for at least 7 days, and waiting a minimum of 30 days before sealing to allow the surface to air dry. We found no published source for when foot traffic is safe; follow whatever instructions the contractor puts in writing.

A few things shape how the curing period goes on any given Ottawa job. The air temperature at the time of the pour matters: the Code's cold-weather rules kick in below 5 °C, and the Code requires that no frozen material or ice be used in the mix. The concrete mix itself matters: the Code sets a minimum compressive strength of 32 MPa for exterior flatwork and garage floors, and a maximum water-to-cementing-materials ratio of 0.45 for those same applications. The Code's appendix notes that adding water to concrete on site may reduce strength and increase the tendency to shrink and crack. How the surface is finished also matters: the National Research Council's Canadian Building Digest 116 notes that over-vibration and excessive trowelling affect entrained air adversely, and that air entrainment has a "remarkable effect" in improving frost resistance.

What to ask before the pour starts:

• What is the specified compressive strength and water-to-cementing-materials ratio for this mix?
• What cold-weather or rain protection is included, and how is it described in the contract?
• When can foot traffic begin, and when does the contractor recommend sealing?
• Are those timelines written into the specification?

The Consumer Protection Act, 2002 requires that a direct agreement over $50 be in writing, signed by both parties, and delivered to you, and gives you 10 days to cancel after receiving it. Getting the curing plan in the written contract means you have something to refer back to if the surface shows problems later.

Before hiring, ask the contractor to show you their City of Ottawa hardscaping contractor licence and then confirm the name against the City's published list of licensed contractors yourself.