How to Cut Fiberglass Rebar on Site Safely

Fiberglass (GFRP) rebar is cut with a high-speed cutter or saw fitted with a diamond or abrasive blade, cutting straight through with the bar supported on both sides. It must not be cut with shears, bolt cutters or a rebar shear, and never with a torch. The cut itself is quick and throws no sparks. The real work is controlling the glass fibre dust and wearing the right protection, and checking the project specification before any field cutting, because some owners restrict it.

This post covers cutting only. Handling, supports, ties and laps for GFRP are in our guide on how to install and tie fiberglass rebar.

Check before you cut

Two things to confirm before anyone picks up a saw:

1. Is field cutting allowed? On ordinary building work it usually is for straight bars. On provincial highway and bridge work in Ontario, the construction specification allows straight GFRP bars to be cut on site only with written permission, using a saw, and does not allow bent bars to be field cut. Our explainer on fiberglass rebar codes, CSA S807 and S806 covers those specifications. Municipal and private specifications may borrow the same rules.
2. Is it a straight bar or a bent one? GFRP bends are formed at the factory while the resin cures. They cannot be re-bent or recreated on site, so a bent bar should never be cut in a way that removes or shortens the bend. If a bent bar does not fit, the fix is a new bar, not a cut. Our post on GFRP corners, L-bars and hooks explains why.

The best cut is the one planned into the bar list. Straight GFRP lengths are set by the manufacturer, so ask for bars in lengths that suit the laps in the design and keep site cutting to trimming and genuine field fits.

What cuts fiberglass rebar

GFRP is glass fibres bound in a cured resin. Cutting it cleanly means grinding or sawing through the fibres, not squeezing them apart.

Tools that work:

• Angle grinder with a cut-off wheel. A diamond blade or an abrasive cut-off wheel. This is the most common site tool for small and medium bar sizes.
• Circular saw or cut-off saw. Fitted with a diamond or abrasive blade suited to the material and rated for the saw's speed. Useful when there are many cuts of the same length.
• Chop saw. For repetitive cuts in a staging area, with the bar fully supported on the infeed and outfeed sides.
• Fine-toothed hand saw. Manufacturers list it as an option for small bars and occasional cuts. Slower, but no power and less airborne dust.

The RSIC Manual of Standard Practice describes field cutting of FRP bars with a high-speed cutter, which is what the first three are. Diamond blades generally hold up better than abrasive wheels in glass fibre; abrasive wheels wear quickly, so check the wheel diameter as you go.

Tools that do not work:

• Rebar shears, bolt cutters and cable cutters. RSIC practice does not permit shear cutting of FRP bar, and manufacturers advise against it. Shearing crushes the end, splits the bar along its length and leaves loose fibres.
• Torches. The resin burns. A torch damages the bar well beyond the cut and gives off smoke and fumes.
• Hacking or snapping. Scoring the bar and breaking it off splinters the end in the same way shearing does.

How to make a clean cut

1. Measure and mark the cut line all the way around the bar with a marker or a wrap of tape. Taping over the cut line also helps limit splintering where the blade exits.
2. Support the bar on both sides of the cut, close to the line, so the offcut does not drop and snap the last fibres before the blade gets through.
3. Clamp or hold it firmly. GFRP is light and springy and will chatter if it is loose.
4. Cut straight through in one steady pass, letting the blade do the work. Forcing the feed heats the blade and the resin and tears the fibres.
5. Inspect the end. It should be square, with no crushed zone, no split running back along the bar and no loose fibres. If the end is damaged, trim it back past the damage.

Cut ends. Some manufacturers and specifications call for cut ends to be sealed with a compatible resin; others do not require it for ordinary work. Follow whichever applies to your bar and project, and do not improvise with paint or general-purpose sealant.

Sand-coated bars are hard on blades. Expect to replace blades and wheels more often than you would on smooth-surfaced composite.

Dust, PPE and site safety

Cutting GFRP produces fine glass fibre dust and loose fibres. They irritate skin, eyes and lungs, and the dust drifts onto other trades and into any enclosed space. Treat it the way you would cutting any fibreglass composite.

Personal protective equipment for the person cutting and anyone close by:

• Eye protection, safety glasses as a minimum and a face shield with a grinder or saw.
• Gloves and long sleeves. Fibres work into skin and are hard to get out.
• A properly fitted respirator suitable for fibre dust, as specified in the manufacturer's safety data sheet.
• Hearing protection with grinders and saws.

RSIC practice simply says proper PPE should be worn during any cutting. The safety data sheet for the specific bar is the document that sets out what that means for the product on your site, so have it on site and follow it.

Controlling the dust:

• Cut outdoors or in a well-ventilated area, downwind of other work where possible. Avoid cutting inside closed formwork or in confined spaces.
• Set up one cutting station rather than cutting wherever bars happen to be. It keeps the dust in one place.
• Use dust extraction where your tool allows it, and clean up with a vacuum suited to fine dust rather than sweeping or blowing it off with compressed air.
• Keep offcuts and dust out of the forms. Loose fibres and dust on the bars or in the forms are debris the inspector can flag.
• Wash up before eating or smoking, and keep work clothes separate.

In Ontario, the employer's general duties under the Occupational Health and Safety Act apply to cutting GFRP like any other dusty task: assess the hazard, provide the equipment and make sure workers know how to use it.

Fiberglass vs steel: how cutting differs on site

GFRP is easier on the arms because it is light and cuts quickly, but it is less forgiving: there is no fixing a bend or a short bar on site. Our GFRP vs steel rebar comparison covers the other practical differences.

Ordering GFRP so the crew cuts less

Most field cutting on GFRP jobs comes from bars that were not detailed to suit the layout. Getting the bar list right before the order saves time on site and keeps dust down:

• Detail straight bars to suit the laps and the manufacturer's available lengths.
• Order every bent shape (corner bars, hooks, stirrups) from the drawings, since none of them can be made on site.
• Allow for spares on field-fit items like bars around openings, where the designer allows them.

We supply GFRP rebar to your specification, alongside steel rebar from 10M to 55M cut, bent and tagged to your bar list. Send your drawings for a take-off and quote, or see our rebar products, including GFRP.