How to Install and Tie Fiberglass Rebar

Fiberglass (GFRP) rebar is installed much like steel, with four differences: it is supported on non-metallic chairs, tied with non-corrosive ties (plastic-coated wire, nylon zip ties or plastic clips), cut only with a high-speed blade, and never bent on site. Laps come from the GFRP drawings, corners are ordered as factory-bent shapes, and because the bar is light, the mat has to be tied and held down so it does not float when the concrete goes in.

This guide covers the site side of a GFRP job, from unloading to pour day. Whether GFRP is the right bar for your project is a design question; our GFRP vs steel comparison covers that.

Before you start: drawings, bars and accessories

A GFRP job needs GFRP drawings. Bar sizes, spacing, laps, cover and bend details are designed for fiberglass under CSA S806 (buildings) or CSA S6 (bridges), with the bar itself made to CSA S807. Substituting GFRP one-for-one into steel drawings is not an installation shortcut; it is a design change the engineer has to make. Our post on GFRP rebar codes explains the standards.

When the bar arrives, check:

• Printed markings. RSIC practice calls for the manufacturer's name, production lot number and bar designation to be printed along each straight bar. Bundles of bent bars carry weatherproof labels instead.
• Grade. CSA S807 classifies bars by their minimum modulus of elasticity: Grade I, II or III. Make sure the grade delivered matches the drawings.
• Bent shapes. Every corner, L-bar, hook and stirrup should be on the delivery, because none can be made on site.
• Accessories. Non-metallic chairs and bolsters, and ties the specification accepts. Some fully non-metallic designs also call for non-metallic form ties.

Handling and storing fiberglass bar

GFRP is tough in the concrete but can be damaged before it gets there. RSIC practice for FRP bar on site:

• Do not drag, drop or impact bars. A bar that has been dropped or shows obvious damage (cracking, crushed fibres, exposed glass) should be removed and replaced.
• Store bars clear of the ground on protective cribbing.
• Cover bars stored outside for long periods with a tarp to protect them from UV. RSIC sets that at more than 8 months outside.
• Lift long lengths with a spreader bar so they do not bend excessively.

GFRP is a fraction of the weight of steel, so most bars can be carried by hand. That makes handling easier on crews, but it also makes bars easy to toss around. Treat them like a finished product, not like black bar.

Cutting fiberglass rebar

Straight GFRP bars can be cut on site, but only one way:

• Use a high-speed cutter with a diamond or abrasive blade. RSIC practice does not permit shear cutting, and a torch is out of the question.
• Wear the right PPE. Eye protection, gloves and a dust mask or respirator. Cutting produces fine glass fibre dust and loose fibres at the cut.
• Control the dust, especially in enclosed spaces and where other trades are working.
• Never cut a bent bar in a way that removes or shortens the bend. The bend is the part that was formed at the factory.

Plan straight lengths on the bar list so cutting is the exception. Owners such as MTO restrict field cutting on their work, as our GFRP vs steel post notes, so check the specification before cutting.

Supporting the mat

Support matters more with GFRP than with steel, for two reasons: the bar is lighter, so concrete can lift it, and it is more flexible, so it sags more between supports.

• Use non-metallic supports. Plastic chairs and bolsters, or precast concrete blocks where the mat bears on soil. Steel chairs would put corrodible metal back into a system chosen to avoid it.
• Space supports closer than for steel where the manufacturer recommends it. Some GFRP makers publish support spacing tighter than steel practice. Our guide to rebar chair spacing covers the steel baseline.
• Use chairs with wide bases or sand plates on granular fill or vapour barrier so they do not sink or puncture.
• Set the height from the cover on the drawings, measured from the base to the underside of the lowest bar.

What to tie fiberglass rebar with

RSIC practice is that FRP bars are secured with non-corrosive material. The usual options:

Whichever you use, the ties have to hold the bars snugly at the intersection. A loose tie lets a light bar slide or lift.

How many intersections to tie. There is no single number. Tie enough to keep the mat from moving during placing and vibration, and tie more densely than you might with steel because GFRP has less weight holding it down. A practical approach is to tie every intersection around the perimeter, at laps, around openings and anywhere the mat will be walked on or where concrete will hit it hard. Follow the bar manufacturer's guidance and the specification where they give a pattern.

Tie the mat to its supports. With steel, weight keeps bars sitting on their chairs. With GFRP, tie the bars to the chairs or bolsters so the mat and its supports move as one unit, and anchor the supports where the concrete could lift them.

Laps, corners and connecting bars

Laps (overlaps). GFRP bars are joined by lap splices. The lap length is on the GFRP drawings. CSA S806 has its own development and splice rules for FRP bar, and RSIC practice defers to the contract drawings for FRP laps. Do not take a lap from a steel chart unless the engineer has confirmed it. Tie each lap at both ends and along its length so the bars stay in contact.

Corners and hooks. GFRP cannot be bent in the field. Continuity around a corner comes from factory-bent corner bars or L-bars lapped with the straight bars. RSIC notes a minimum bend diameter of at least three bar diameters, formed by the manufacturer before the resin cures. See GFRP corners, L-bars and hooks and can you bend fiberglass rebar for ordering bent shapes.

Dowels and connections. Dowels into existing concrete or between pours are detailed on the drawings, in GFRP or in another material the designer chooses. GFRP cannot be welded, so any connection that relies on welding a bar to a plate has to be redesigned.

Pour day

• Walk the mat before the pour. Check bar size, spacing, cover, laps and ties against the drawings. Inspectors check GFRP against the GFRP drawings, not steel ones.
• Protect the mat from traffic. GFRP is less stiff than steel, so use boards or runways where crews and hoses will cross it.
• Keep the vibrator off the bars. Vibrate the concrete, not the reinforcement, and watch for any section of mat starting to lift.
• Place concrete so it does not push the mat. Dropping concrete in one heavy load can shift light bar. Placing in smaller amounts and spreading it helps.
• Recheck height as you go. If a chair tips or a tie breaks, fix it before the concrete covers it.

Getting GFRP on site ready to place

The easiest GFRP job is one where every straight length and bent shape arrives labelled to a bar list that matches the drawings. We supply GFRP rebar to your specification alongside steel bar from 10M to 55M. Send your drawings for a quote, or see our rebar products.