What PSI concrete should be used for a garage floor in NB?

A garage floor in New Brunswick should be poured with a minimum 4,000 PSI (30 MPa) concrete mix, and many contractors specify 4,500 PSI (32 MPa) for added durability. Standard 3,500 PSI (25 MPa) concrete is appropriate for many interior applications, but a garage floor sees vehicle traffic, oil and chemical exposure, thermal shock from hot tires, and potentially freeze-thaw cycling near the door — all of which benefit from higher strength concrete.

In Canada, concrete strength is typically specified in megapascals (MPa) rather than PSI, so here's the conversion reference:

• 25 MPa = 3,625 PSI — general interior use, NOT recommended for NB garage floors


• 30 MPa = 4,350 PSI — standard for NB garage floors, suitable for typical residential vehicles


• 32 MPa = 4,641 PSI — preferred for heavier use, better chemical resistance, ideal for workshops


• 35 MPa = 5,076 PSI — commercial grade, used for heavy vehicle or industrial garage applications

For most NB homeowners with a standard two-car attached garage, 30 MPa (4,000 PSI) is the sweet spot — it's widely available from NB ready-mix suppliers, provides excellent durability for passenger vehicles and light trucks, and costs modestly more than lower-strength mixes.

Critical Specifications Beyond PSI

Strength alone doesn't determine durability. For an NB garage floor, these specifications matter equally:

Water-to-cement ratio should be 0.45 or lower. A lower ratio means less water in the mix, which means fewer voids and better strength. Never allow water to be added to the truck at the jobsite — this raises the water-cement ratio and directly weakens the finished floor.

Air entrainment: The section of your garage floor near the door sees outdoor freeze-thaw conditions. An air-entrained mix (4–7% air content) is important for that zone. Some contractors pour the entire slab with air-entrained concrete for simplicity; others use non-air-entrained for the interior portions where maximum strength is preferred (air entrainment slightly reduces compressive strength at equivalent mix proportions).

Fibre reinforcement: Adding polypropylene synthetic fibres ($15–$25 per cubic yard added cost) reduces plastic shrinkage cracking and improves impact resistance. It's a good addition for garage floors and is specified more and more frequently by NB contractors.

Slump: Specify 4-inch slump for garage floors. A wetter mix is easier to pour but produces a weaker, more crack-prone slab. Resist the temptation to add water if the concrete seems stiff on a hot July day in Moncton — ask the ready-mix driver to use a water reducer (superplasticizer) instead.

Ready-mix concrete in NB (delivered) costs $190–$260 per cubic yard depending on strength and admixtures. A two-car garage floor uses roughly 5–7 cubic yards. New Brunswick Concrete can connect you with experienced garage floor contractors who specify and order the right concrete mix for your project.