Types of Fiberglass Rebar: Coatings, Colours and Grades

Fiberglass rebar comes in several types, and the differences that matter are the fibre, the resin, the stiffness grade, the surface finish and the shape. Colour is not one of them. A green bar, a white bar and a black bar can be very different products or nearly identical ones; the tag and the data sheet tell you which. In Canada, the property that decides most structural specifications is the CSA S807 grade, which sorts bars by stiffness.

This post walks through each way GFRP bars differ, what each difference means for your job, and how to tell what you are actually getting. If you are new to the material, start with what GFRP rebar is.

How fiberglass rebar types differ at a glance

Fibre: glass, basalt and the rest

The "G" in GFRP is glass. Glass fibre is by far the most common reinforcement fibre in construction bar. Our code post notes that the 2019 edition of CSA S807 covers bars made with glass, carbon, aramid or basalt fibres, and added basalt and some glass fibre to its corrosion-resistant category.

What that means in practice:

• Glass (GFRP). The everyday product for slabs, foundations, walls, bridge decks and marine work.
• Basalt (BFRP). Made from basalt rock fibre. It looks a lot like fiberglass bar but is usually dark brown or black, because basalt fibre is naturally dark. It is a different material with its own properties, so it should not be swapped for a specified GFRP bar without the designer's approval. MTO accepts glass fibre only, so basalt bar is not an option on MTO work.
• Carbon and aramid. Much less common as everyday reinforcing bar and mostly found in specialist and strengthening work.

If a bar is sold simply as "fiberglass rebar", confirm the fibre type on the data sheet.

Resin: the part that protects the glass

Glass fibres on their own do not survive well in wet, alkaline concrete. The resin around them is what keeps moisture and alkali out, so the resin type is a large part of a bar's durability.

• Vinylester and epoxy resins are associated with the higher durability class under S807 and are the usual choice for structural bar.
• Polyester resin shows up in economy or "non-structural" product lines. One Canadian manufacturer sells a polyester line it recommends only for applications where stresses are negligible, such as shrinkage and crack control in slabs on grade, and states that its vinylester bar has superior durability.

That split is worth knowing, because two bars of the same diameter and colour can sit on opposite sides of it. For anything an engineer has designed, use the resin and durability class the drawings call for. For more on long-term durability, see our upcoming post on whether fiberglass rebar rusts.

Grades: CSA S807 sorts bars by stiffness

Steel rebar grades such as 400W describe yield strength. GFRP has no yield point; it stays elastic until it breaks. So CSA S807 grades GFRP by modulus of elasticity, which is a measure of stiffness.

• Grade III is the stiffest grade. Stiffer bars deflect less and crack less under the same load, so they need less bar to meet serviceability limits. MTO's material specification for Ontario bridge work calls for Grade III bar in durability class D1; our CSA S807 and S806 post covers how MTO treats GFRP.
• Grades I and II have lower minimum stiffness and suit work where deflection and crack width are less critical.
• Strength is listed separately. Guaranteed tensile strength is given for each bar size, and it drops as bar diameter increases.

Manufacturers publish the modulus of each product on their data sheets. One Canadian maker, for example, sells bars in 46, 50 and 60 GPa stiffness grades. Always compare the grade and modulus on the data sheet with what the drawings specify, rather than assuming "fiberglass rebar" is one thing.

GFRP bar sizes do not line up exactly with steel M sizes either, even when suppliers use similar labels. Our GFRP size and weight chart shows the S807 designated diameters and areas.

Surface finish: how the bar grips the concrete

A smooth glass rod would slip in concrete, so every structural GFRP bar has a surface treatment to create bond. The main types:

• Sand coated. Sand is bonded to the bar surface with resin, giving a rough, gritty finish. Very common in Canadian-made bar.
• Helically wrapped. A fibre strand is wound around the bar to form a spiral ridge, often combined with a sand coating.
• Deformed or ribbed. Ribs or indentations are formed into the bar surface, closer to the look of steel rebar.

Each surface bonds differently, and designers account for bond in development and lap lengths. That is one reason not to substitute one manufacturer's bar for another's partway through a job, even at the same size and grade, without the engineer's sign-off. Handle sand-coated bars with gloves; the coating and any exposed fibre at cut ends are hard on bare hands.

Colours: what green, white and black mean

GFRP bar colour comes from the resin system, pigments and coating, and it varies by manufacturer. You will see:

• Green. Common enough that some people call all GFRP "green rebar". It is a colour, not a type. Green bar is used for the same work as any other GFRP: slabs, driveways, foundations, walls and corrosive exposures, within its data sheet and the design.
• White or light. Some Canadian bar is white or off-white, and one maker promotes its white colour for decorative and architectural concrete.
• Other colours. Brand choices, nothing more.
• Black or dark brown. Often basalt (BFRP) rather than glass, though some glass bars are pigmented dark.

No Canadian standard assigns colours to grades. The only reliable identification is the tag and the manufacturer's data sheet showing the fibre, grade, durability class and the standard the bar is certified to. Colour is useful on site for one thing: telling two different products apart in the same delivery.

Shapes and forms

GFRP also differs in the forms it comes in:

• Straight bars in stock or cut lengths. Our upcoming post on GFRP lengths, coils and bundles covers what is typical.
• Factory bent shapes: L-bars, U-bars, hooks, stirrups and spirals. Structural GFRP uses a thermoset resin that cannot be re-bent once cured, so every bend is made at the factory and has to be on the order. See GFRP corners, L-bars and hooks.
• Grids and mesh. CSA S807 covers grids as well as bars. Our upcoming post on fiberglass and coated rebar mesh compares the slab options.

How to choose and check what you are getting

1. Start from the drawings. The engineer specifies the grade, durability class and sometimes the manufacturer. Order to that, not to colour or price alone.
2. Ask for the data sheet and certification showing S807 compliance for the exact product.
3. Order by designated diameter and nominal area, not by a steel-style label.
4. List every bent shape on the bar list, since none can be made on site.
5. Keep one product per element unless the designer approves a change.

Getting GFRP specified and supplied

If your drawings call for GFRP, or you want to compare it with steel, send them through our quote request form. We supply GFRP rebar alongside steel bar from 10M to 55M, prepare free take-offs and quotes, and deliver across the GTA and Ontario. See our rebar products for the bar we supply and fabricate.