Fiberglass (GFRP) rebar works in slabs on grade, driveways and garage floors, and its main advantage there is simple: it doesn't rust when de-icing salt gets into the concrete. That matters in Ontario, where cars carry salty slush into garages all winter and driveways get salted directly. But GFRP is much less stiff than steel, can't be bent on site, and doesn't fix the things that cause most slab cracks. Whether it's worth it depends on the slab, not the bar.
This post is about using GFRP in flatwork. For the material comparison in general, see GFRP vs steel rebar, and for the code status of the bar, see does fiberglass rebar meet code.
Why road salt makes this question come up
Steel in concrete is protected by the concrete's alkalinity. Chlorides from de-icing salt slowly work their way in through the surface and cracks. When enough chloride reaches the steel, it starts to rust, the rust takes up more room than the steel, and the concrete above it cracks and spalls. Rust stains bleeding through a garage floor or a driveway are often the first sign.
GFRP doesn't corrode, so it takes that particular failure off the table. That's the same reason it's used on bridge decks and parking structures. In a driveway or garage floor, the question is whether that benefit is worth it for a slab that's lightly loaded, sitting on the ground, and often unreinforced to begin with.
Does a slab, driveway or garage floor need rebar at all?
Start here, because the answer changes the comparison.
- Basement and garage floors in houses. Section 9.16 of the 2024 Ontario Building Code covers floors-on-ground. It sets a minimum concrete thickness of 75 mm (Article 9.16.4.3.), granular base requirements (with garage slabs exempted from the granular layer in Sentence 9.16.2.1.(2)), and drainage, but it does not require reinforcement. Floors-on-ground in Section 9.16 are not structural, and a slab that supports the building has to be designed under Part 4.
- Driveways. A residential driveway isn't a building, so Part 9 doesn't prescribe how it's built. The contractor's or designer's specification governs.
- Structural slabs. Suspended slabs, slabs over a garage or cold room, and slabs carrying walls or columns are engineered, and the reinforcement is whatever the engineer specifies.
So for many Ontario house slabs, reinforcement is a choice made to control crack widths and keep pieces together if cracks form, not a code requirement. Our post on slab-on-grade rebar requirements goes through when it's needed and when it isn't.
Fiberglass rebar vs steel for a concrete slab
| Factor | Steel rebar or mesh | GFRP rebar |
|---|---|---|
| Corrosion from road salt | Rusts once chlorides reach it | Does not rust |
| Stiffness | About 200 GPa | 60 GPa minimum for Grade III, about a third of steel |
| Crack width control for the same amount of bar | Better | Wider cracks unless more bar is used |
| Weight | Heavier | A fraction of steel's weight |
| Bending | Shop or field bent | Factory bends only |
| Cutting on site | Shear, saw or torch | Saw only, with dust protection |
| Staying in position during the pour | Heavier, stays put on chairs | Light, needs secure tying so it does not float |
| Cost per metre of bar | Lower | Higher |
Stiffness values are from CSA G30.18 and the CSA S807 grade requirements, as covered in our GFRP vs steel comparison.
The row that matters most for a slab is stiffness. In a slab on grade, reinforcement mostly works after the concrete cracks, by holding the crack tight. A less stiff bar stretches more at the same stress, so the crack opens wider. That's why a GFRP slab design often uses more bar or closer spacing than a steel design, and why swapping 15M steel for "15M" GFRP at the same spacing isn't the same slab.
Bar labels are another trap. Some GFRP bars sold as 10M have a nominal area of about 71 mm², against 100 mm² for steel 10M. Order by the nominal area and grade on the drawings, not the size label.
Is fiberglass rebar good for a driveway?
It can be a good fit when:
- The driveway sees heavy salt and you want to avoid rust staining and spalling over the long term.
- There's a reason to reinforce at all, such as poor or variable subgrade, a slab that bridges a trench or backfilled area, or heavier vehicles.
- The contractor knows how to handle it, including tying it down, supporting it on chairs and planning bends in advance.
It's less likely to be worth the premium when the driveway is going to be unreinforced or lightly reinforced anyway, or when the real risk is a soft base. Driveways crack mostly because of the subgrade, drainage, joint spacing and the concrete itself. GFRP fixes none of those.
Surface scaling is a separate problem. Salt damages the concrete surface through freeze-thaw scaling, regardless of what reinforcement is inside. That's controlled by the concrete mix (air entrainment, strength and water-cement ratio for the exposure class), finishing and curing. Under CSA A23.1, plain concrete exposed to chlorides and freeze-thaw, such as garage floors and sidewalks, is typically exposure Class C-2. Our post on concrete cover for rebar explains the exposure classes.
If you're deciding between mesh and bar first, see our comparison of wire mesh vs rebar for a concrete driveway.
Fiberglass rebar for a garage floor
Garage floors have the strongest case for GFRP among house slabs, because salty meltwater sits on them for months. A few points specific to garages:
- Slope and drainage to the door or a drain keep salt water from pooling. That does more for the slab's life than any reinforcement.
- Joints placed where the slab wants to crack (re-entrant corners, around columns, at regular spacings) keep cracks where you want them.
- Dowels and edge bars. Where the slab ties into a foundation wall or an adjacent slab, any bent bars or dowels must be ordered as factory GFRP shapes or detailed in steel. GFRP can't be bent on site. See GFRP stirrups and dowels vs steel.
For the mesh versus bar question in garages, see wire mesh vs rebar for a garage floor.
Fiberglass rebar spacing and placement
We won't give a spacing, because there isn't a correct one without the slab design. Spacing depends on slab thickness, the loads, the joint layout and the bar's stiffness and area. Use the spacing on your drawings. If you don't have a design and want GFRP, have a designer specify it rather than copying a steel spacing.
What we can say about placement:
- Keep it at the depth shown. Reinforcement that ends up on the subgrade does almost nothing. Support it on non-metallic chairs at the depth on the drawings and don't rely on "pulling it up" during the pour.
- Tie it securely. GFRP is light, and concrete can lift bar that isn't tied down.
- Plan laps and bends. Lap lengths for GFRP come from the design, not from steel lap charts, and every corner bar must be ordered bent.
- Protect it in storage. Keep bundles covered; sunlight degrades the resin over time.
- Cut with a saw and use dust protection.
Steel, mesh, GFRP or fibres?
| Option | Where it fits |
|---|---|
| Unreinforced slab with good joints | Many basement floors and lightly loaded slabs on a good base |
| Welded wire mesh | Light crack control where the mesh is properly supported |
| Steel rebar | Most reinforced slabs, structural slabs, heavier loads |
| GFRP rebar | Salt-exposed slabs where long-term corrosion matters |
| Fibre-reinforced concrete | Plastic shrinkage control; not always a replacement for bar |
Fibres are a different product from fiberglass rebar, despite the similar name. Our post on whether fibre concrete replaces rebar explains the difference.
Getting GFRP or steel priced for your slab
We supply GFRP rebar to your specification, and steel rebar cut, bent and tagged to your bar list. If your designer is weighing both, we can quote each from the same drawings so you're comparing the same slab. Send your drawings or slab details, or see our rebar products.
Frequently asked questions
Is fiberglass rebar good for a driveway?
It can be. GFRP does not rust, so it suits driveways and garage floors exposed to Ontario road salt, where corroding steel can crack and stain the concrete. It is less stiff than steel, so the amount and spacing of bar should come from a design rather than a one-for-one swap.
Can I use fiberglass rebar in a concrete slab?
Yes. GFRP is used in slabs on grade, garage floors, patios and driveways. Part 9 of the Ontario Building Code does not require reinforcement in ordinary floors-on-ground, so where it is used it is a design choice, and the designer sets the bar size, spacing and depth.
What spacing should fiberglass rebar have in a slab?
There is no single answer. Spacing depends on slab thickness, loads, joint layout and the bar's stiffness, and GFRP often needs more bar or closer spacing than steel to control cracks. Use the spacing on your drawings or ask your designer.
Fiberglass rebar vs wire mesh for a garage floor: which is better?
They do different things. Mesh and steel bar are cheaper per square metre and familiar, but rust when salt reaches them. GFRP resists salt but costs more per metre and needs careful support. For many garage floors, a good base, proper joints and durable concrete matter more than which reinforcement is used.
