Does the Code set a curing time for patios in Ontario?

Only for cold-weather work does Ontario's 2024 Building Code set a time: when the air temperature is below 5 °C, concrete must be kept at not less than 10 °C for 72 hours after placing. Outside of that cold-weather trigger, we found no curing time in the Code for a patio, walkway or any exterior flatwork.

The Code does specify that compressive strength is measured at 28 days, and its appendix note warns that adding water to concrete on site can reduce strength and increase the likelihood of shrinkage cracking. Those are the only time figures we found in the Code for exterior concrete. We found no statement in the Code on whether those provisions legally bind a patio built without a permit; 32 MPa is the Code standard for exterior flatwork.

For practical curing guidance, the Ready Mixed Concrete Association of Ontario, an industry association, recommends maintaining a satisfactory moisture content and temperature for a minimum of 7 days. That is industry guidance, not law. We found no published source for when foot traffic is safe; the contractor's written instructions govern that.

A few things worth putting in writing before the pour:

• the curing method and duration the contractor will follow
• what protection is planned if the air temperature drops below 5 °C during or after the pour
• what happens if rain falls on the fresh surface (we found no published rule; the protection plan belongs in the specification)
• the concrete strength specified (32 MPa for exterior flatwork is the Code standard)

If the patio project involves any digging for a base or footings, whoever digs is the excavator under the Ontario Underground Infrastructure Notification System Act, 2012, and a locate request must go through Ontario Dig Authority at least 5 business days before the ground is broken, so confirm with your contractor who will be submitting that request before work starts.