Does NB spring frost heave affect freshly poured concrete?

Yes — spring frost heave is one of the most damaging forces acting on concrete in New Brunswick, and it is especially dangerous for concrete that was either poured too late in fall or poured too early in spring before the ground has fully stabilized.

Frost heave occurs when water in the soil freezes and expands, physically lifting the soil — and anything sitting on top of it — upward. The movement can be impressive: heave of several inches is not unusual in NB's clay-heavy or poorly drained soils. When a concrete slab, footing, or foundation wall is caught between frozen ground below and a frozen slab above, the expansive forces are enormous. Slabs crack, footings crack, and in severe cases, foundation walls can shift or bow.

The good news is that properly designed concrete structures are protected from frost heave — not because the concrete resists it, but because the footings are placed below the frost line. NB Building Code requires structural footings to extend a minimum of 4 feet (1.2 metres) below grade in southern NB (Moncton, Fredericton, Saint John) and 4.5–5 feet in northern NB (Bathurst, Campbellton). Below the frost line, the ground does not freeze, so footings do not heave.

Where heave does damage concrete is in flatwork — driveways, patios, sidewalks, and garage aprons — that is not attached to the frost-protected foundation system. These slabs sit on the surface and move with the soil. In spring, the thaw happens unevenly from the top down, and slabs that were frozen in place all winter can lift, tilt, and settle in new positions. This is why control joints are critical: they allow slabs to move and crack in controlled locations rather than randomly.

Freshly poured spring concrete is particularly vulnerable. If you pour while any frost remains in the subgrade, the concrete will settle as the soil thaws beneath it — often cracking within the first season. Wait until the ground is fully thawed and any saturated, frost-softened soil has been excavated and replaced with properly compacted granular fill before pouring.

For patios and driveways in areas with poor drainage or clay soils — common in the Moncton and Fredericton areas — a deeper granular base (8–12 inches of compacted clear stone) helps manage frost by improving drainage and reducing ice lens formation. Get matched with a local concrete contractor through New Brunswick Concrete to assess your site's specific drainage and soil conditions.