How thick should a concrete patio slab be in NB?

A concrete patio slab in New Brunswick should be a minimum of 4 inches (100 mm) thick — and in areas that will see any vehicle traffic, heavier furniture, or hot tub loads, 5-6 inches is strongly recommended.

Four inches is the industry-standard minimum for residential pedestrian-use concrete flatwork, and it applies directly to NB patios. A 4-inch slab over a properly prepared 6-inch compacted gravel base provides sufficient strength for outdoor furniture, foot traffic, barbecues, and typical residential use. The critical caveat in NB is that 4 inches is only adequate when the base preparation, concrete mix, and reinforcement are all done correctly — skimping on any one of those elements means the slab will crack, shift, or deteriorate faster than it should.

Base preparation is as important as slab thickness in NB. The freeze-thaw cycle that causes frost heave affects the soil beneath your patio as much as the concrete surface above. A minimum 6-inch layer of compacted granular gravel (crushed limestone or clean stone) beneath the slab provides drainage and reduces frost heave by minimizing moisture retention in the sub-base. In areas of Fredericton, Miramichi, or Riverview with clay-heavy soils — which hold water and heave significantly — a deeper gravel base (8-10 inches) is worth the extra cost.

Reinforcement in a 4-inch slab. Welded wire mesh (6x6 W1.4/W1.4) placed at mid-slab height on chairs is standard for residential patio slabs. The mesh does not prevent cracking — it holds pieces together after cracking occurs, maintaining the slab's integrity and preventing differential settlement between sections. Rebar (10M at 18-inch centres) is a stronger option for slabs that will support significant loads like a large hot tub or a structure.

For a patio that will support a hot tub, increase thickness to 5-6 inches and add rebar rather than mesh. A fully loaded hot tub can weigh 3,000-5,000 kg — spreading that load requires a thicker, better-reinforced slab than a standard patio. Many NB homeowners build a separate thickened pad (6 inches with rebar) for the hot tub location and tie it into a standard 4-inch patio surrounding it.

For vehicle access — if any part of the patio will be driven on or parked on — step up to at least 5-6 inches with rebar reinforcement. Thin residential patio slabs will crack under vehicle loads, particularly after frost heave has created any unevenness in the base. The cost difference between 4 and 5 inches of concrete on a 300 square foot patio is roughly $200-$400 in materials — a minor cost compared to the expense of a premature repair or replacement.