Foundations & pads

There is no cost difference, and both are code. Fiberglass never rusts, so it wins on long-term crack prevention through freeze-thaw. Steel bends instead of snapping, so it wins under heavy point loads like a hoist. We ask what the garage will carry and build to that.

Because it is the one place you can verify. Pads can be poured thicker in the middle and at the edges, so a thickness quoted 'in the slab' can mean almost anything. The apron number is the one we put in writing.

A chair is a small stand that holds the bar off the gravel so it ends up in the middle of the slab instead of the bottom. Rebar only works where it sits: at the bottom it reinforces the bottom inch and leaves the top to crack. Chairs make the pour harder, because the crew cannot walk the grid down and the concrete has to come in by pump, which is why they are an upgrade rather than the default. Worth it under a hoist, a heavy truck or an RV; a car garage on the standard grid does fine without them.

They do different jobs. The MPa number is how hard the concrete is in compression, which is what a tire load tests. The rebar carries tension when the ground moves, and its spacing decides how far a crack can travel before it meets steel. A tighter 18 inch grid controls cracking better than the standard 24 inch; a 40 MPa mix wears harder than 32. If the pad is going to carry something heavy, thickness comes first, then the grid, then the mix. Going from 32 to 40 MPa on a 4 inch slab helps less than going to 5 inches.

Ours are poured at 32 MPa as standard, with 40 MPa available. Most garage pads that fail here do not fail because the concrete was too soft. They fail because water got under the slab, the gravel base moved, or the reinforcement was lying on the ground. That is why the standard pad spends its budget on the base and tied rebar before it spends it on a harder mix.

The pour and the first cure take about a week before the framing crew loads it. Concrete keeps gaining strength for about a month, so the garage is being built on top of it while it finishes curing. By the time the doors hang it is ready for the truck.

For a garage on a flat lot with cars and a shop in it, the floating slab is the standard and the right answer. A frost wall puts footings below the frost line so the structure cannot heave, and it is required the moment there is living space above the garage. It also suits a sloped lot. Deciding at the pour is what keeps a suite possible later.