Fusion-bonded epoxy-coated rebar is ordinary steel reinforcing bar that has been blast-cleaned, heated and sprayed with a dry epoxy powder in a coating plant. The powder melts on the hot steel, flows into the blasted surface and cures in seconds into a tough, continuous film. "Fusion-bonded" refers to that step: the coating is fused onto the bar by heat rather than painted on. There are two main routes, bar coated straight and then bent (ASTM A775/A775M, usually green) and bar bent first and then coated (ASTM A934/A934M, usually purple or grey), plus dual-coated bar with zinc under the epoxy.
This post walks through how the coating is applied, how the types differ, what quality checks happen in the plant, and why the process cannot be copied on a job site.
The coating process, step by step
North American coating lines follow the same basic sequence. The Epoxy Interest Group, a US industry group for coated bar, describes four main steps:
1. Surface preparation
The bar starts as standard reinforcing steel. On Canadian work, the RSIC Manual of Standard Practice says bars to be coated must meet CSA G30.18 and be free of oil, grease, paint and similar contaminants.
The bars are then blast-cleaned with abrasive grit to a near-white metal finish. Blasting removes mill scale, rust and salts, and it leaves a roughened surface profile that the coating can grip. Surface preparation is the step most closely tied to how well the coating sticks, and plants inspect the blasted surface before coating. Some Canadian specifiers also require a primer at this stage to improve adhesion; the RSIC manual notes that a primer, with modern coatings and quality assurance, slows water penetration at the steel surface.
2. Heating
The clean bar is heated, typically by electrical induction, to around 230°C (450°F), according to the Epoxy Interest Group. Some plants use gas-fired heating. Steel temperature is monitored, because the powder needs the steel in the right temperature range to flow and cure properly.
3. Electrostatic powder application
The hot bar passes through a spray booth where dry epoxy powder is applied with an electrostatic charge. The charged particles are attracted to the grounded steel and wrap around the bar, including the ribs. On contact with the hot surface, the powder melts and flows into the blast profile.
4. Cure and cooling
The epoxy is a thermosetting resin. As it cures, its molecules cross-link into a hard, chemically stable film. The Epoxy Interest Group describes a cure of roughly 30 seconds. Some plants then quench the bar with air or water to cool it for handling.
The result is a film a few hundred micrometres thick, with thickness limits set by the coating specification. It isolates the steel from moisture and chlorides as long as it stays intact. How that protection works, and its limits, are covered in our comparison of epoxy-coated vs standard rebar.
Types of epoxy-coated rebar
The coating chemistry is similar across types. What differs is when the bar is bent and what is under the epoxy.
| Type | Standard | Sequence | Usual colour |
|---|---|---|---|
| Coated straight, fabricated after | ASTM A775/A775M | Straight bar coated in long lengths, then cut and bent | Green |
| Fabricated, then coated | ASTM A934/A934M | Bar cut and bent to shape first, then coated as a finished piece | Purple or grey |
| Dual-coated | ASTM A1055/A1055M | Zinc layer applied first, epoxy over it | Varies by producer |
A775 bar is the common route in North America. Coating straight bar on a continuous line is efficient, and the coating is formulated to survive bending afterwards. The downsides are that every bend stretches the film on its outside face and every cut exposes bare steel that has to be patched.
A934 bar is coated after fabrication, so bends and ends are covered by the plant coating. Fewer plants can do it, handling finished shapes on a coating line is slower, and the coating is not meant to be bent again. Our post on bending and cutting epoxy-coated rebar explains what each type allows after coating.
Dual-coated bar puts a zinc layer under the epoxy, so the zinc can protect the steel at a scratch or holiday in the epoxy. Some specifiers use it as a middle option between epoxy and galvanized bar.
Colour is a convention, not a specification. Green epoxy is so common that people use "green rebar" to mean epoxy-coated bar, while purple or grey usually signals A934 bar. Always read the tag and the certification, not the colour.
On Ontario provincial projects, the Ontario Provincial Standard Specifications (OPSS) set their own material, application and handling requirements for coated bar, which the RSIC manual lists alongside the ASTM standards.
Quality control in the coating plant
The coating only protects the bar if it is continuous, the right thickness and well bonded. The RSIC manual lists the quality control a coating plant is expected to run:
- Visual inspection of the blasted steel surface.
- Monitoring of primer application, where a primer is used.
- Monitoring of steel temperature.
- Keeping production samples of the epoxy powder.
- Electronic holiday detection, which finds pinholes and gaps in the film.
- Monitoring of coating thickness.
- Bend tests to confirm the coating is flexible enough.
- Sampling and testing for adhesion.
- Documenting and keeping the test results.
The Concrete Reinforcing Steel Institute (CRSI) runs a voluntary certification program for epoxy coating plants with third-party inspections, and the RSIC manual recognizes it. Some owners and project specifications require bar from a certified plant, and the plant's certification usually goes into the epoxy-coated rebar submittal.
Can you epoxy coat rebar on site?
Not to any structural specification. Fusion bonding depends on grit blasting, controlled heating and electrostatic powder application, which only happen in a plant. Brushing or spraying epoxy paint onto black bar on site produces a different product with none of the testing behind it, and an engineer specifying epoxy-coated bar will not accept it.
What does happen on site is repair:
- Cut ends and damaged spots on plant-coated bar are patched with an approved patching compound, applied following the patch manufacturer's instructions.
- The RSIC manual limits repaired damage to less than 2% of the bar's surface area per metre.
- Most damage happens during handling and concrete vibration, so padded handling, nylon slings, coated or non-metallic ties and chairs, and plastic-tipped vibrators are common requirements.
- The coating is sensitive to ultraviolet light, so coated bar should be stored under cover and off the ground.
Our guide to epoxy-coated rebar touch-up and field repair covers the patching side in more detail.
Is epoxy coating the right choice?
Fusion-bonded epoxy is a proven, widely specified coating, but its protection depends on an intact film, careful handling and good repairs, and some owners now prefer other corrosion-resistant options for the most severe exposures. Galvanized bar, stainless bar and GFRP all compete for the same jobs, and the right answer comes from the engineer and the owner's specification.
Procut does not supply epoxy-coated bar. We detail, cut and bend black rebar from 10M to 55M and supply GFRP rebar, a non-metallic option for corrosive exposures where the design allows it. Send us your drawings for a quote, or see our rebar products.
Frequently asked questions
What is fusion-bonded epoxy coated rebar?
It is steel rebar coated with a dry epoxy powder that is sprayed electrostatically onto blast-cleaned, heated bar. The powder melts, flows and cures into a continuous plastic film bonded to the steel.
Why is epoxy-coated rebar green?
Colour is a manufacturer convention, not a grade. Bar coated straight and fabricated afterwards (ASTM A775) is usually green; bar bent first and coated afterwards (ASTM A934) is usually purple or grey.
What are the types of epoxy-coated rebar?
The main types are bar coated straight and then cut and bent (ASTM A775/A775M), bar fabricated first and then coated (ASTM A934/A934M), and dual-coated bar with zinc under the epoxy (ASTM A1055/A1055M). Ontario provincial work also has its own OPSS requirements.
Can you epoxy coat rebar yourself?
Not to a structural specification. Fusion-bonded coating needs blast cleaning, controlled heating and electrostatic powder application in a plant. On site, liquid patching compounds are used only to repair cut ends and damage on bar that was plant coated.
