Epoxy-Coated Rebar Touch-Up and Field Repair

Damaged epoxy-coated rebar is touched up with the two-part epoxy patching material approved for the coating, applied to clean, dry steel following the patch manufacturer's instructions. Under RSIC practice every visible defect is patched, and the total repaired area must stay below 2% of the bar's surface area per metre; bars damaged beyond that are replaced. Cut ends are always patched. A can of general-purpose "epoxy" spray paint is not the approved patching material, and it will not satisfy an inspector on a specified job.

This post is the site crew's and inspector's view of touch-up: what counts as damage, what to patch with, how to do it, and when a bar is past saving. Cutting and bending coated bar is covered separately in can you bend or cut epoxy-coated rebar.

Why touch-up matters so much

Epoxy-coated rebar protects the steel with a fusion-bonded epoxy film. The coating only works where it is continuous. A bare spot is a place where chlorides can reach the steel, and because the coating around it is intact, any corrosion that starts there is concentrated on that small area rather than spread over the bar.

That is why specifications treat coating damage seriously and why owners such as transportation agencies inspect it closely.

What counts as damage

Look for anything that exposes steel or thins the film:

• Scratches, gouges and nicks from dragging, bundling, hoisting with chains or wire rope, or walking on the bars.
• Crushed coating under bundle straps, chains or dunnage.
• Cut ends from shearing or sawing, in the shop or on site.
• Cracking or disbonding at bends, especially on bars bent tighter than coated bar allows or bent on site in cold weather.
• Damage from metal accessories, such as bare wire ties or uncoated chairs rubbing through the coating.
• Damage from vibrators. The RSIC Manual of Standard Practice notes that studies have found most damage to epoxy-coated steel comes from vibrating concrete with uncoated vibrator tips.

Holidays (tiny pinholes in the film) are found at the coating plant with electronic holiday detection as part of quality control. On site, inspection is visual, so the focus is on handling and placing damage.

Weathering is a separate issue. RSIC calls for coated bar to be stored under cover because ultraviolet light reduces the coating's effectiveness. Chalky, faded bars that sat outside for a long time should be raised with the inspector rather than patched over.

The limit: when to repair and when to reject

RSIC practice sets out the basic rule for coated bar on site:

• Patch all visible damage with an approved patch compound, according to the patch manufacturer's instructions.
• Keep total repaired damage under 2% of the surface area per metre of each coated bar.

A bar that would need more than that is rejected and replaced, not patched. Project specifications, including the Ontario Provincial Standard Specifications used on provincial and many municipal jobs, can set tighter limits or add rules of their own, so the contract specification always governs.

To put 2% in perspective: the surface area of one metre of 15M bar is roughly 0.05 m² (based on its nominal 16 mm diameter), so 2% is on the order of 10 cm² per metre. A handful of chain scuffs can use that up. Bars that have been dragged off a truck are often over the limit before anyone counts.

What to patch with

The patching material is part of the coating system, not a generic paint. RSIC practice requires coating and patching materials to comply with OPSS 1443, or ASTM A775 and ASTM D3963, along with any local, municipal and provincial specifications.

In practice that means:

• Use the product named in the specification or approved in the submittal. Coating applicators normally supply or recommend a compatible patching compound with the bar. Our post on epoxy-coated rebar submittals covers how it gets approved.
• It is usually a two-part epoxy that is mixed on site and brushed or daubed on. CRSI's handling guidance also calls for cut ends to be coated with two-part epoxy patching material.
• Check the product data sheet for minimum application temperature, pot life once mixed and cure time before concrete. Many two-part epoxies cure slowly or not at all in cold weather, which matters on Ontario jobs for much of the year.
• Keep enough on site. Running out of patching material on pour day is one of the most common reasons damage goes unpatched.

About spray cans. Searches for "epoxy coating spray for rebar" usually turn up general-purpose aerosol paints. Whatever the format, the test is whether it is the patching material the specification accepts. A hardware-store spray, even one labelled epoxy, is not, and an inspector who sees it will ask for the bar to be repatched.

How to touch up epoxy-coated rebar

Follow the patch manufacturer's instructions where they differ, but the sequence is generally:

1. Find and mark the damage. Inspect after the bars are placed and tied, because placing causes damage too. Mark each spot with a paint stick or tape.
2. Clean the area. Remove loose and disbonded coating, dirt, oil, concrete splatter and any rust from the exposed steel, using the method the patch manufacturer calls for. If the instructions call for it, lightly roughen the sound coating around the spot so the patch bonds to it.
3. Make sure it is dry. Moisture under a patch prevents bonding.
4. Mix the patching material in the ratio specified, and only as much as can be used within its pot life.
5. Apply it over the bare steel and onto the surrounding sound coating, building the film to the thickness the instructions call for. Coat cut ends fully, including the end face.
6. Let it cure before the bar is covered with concrete or disturbed. Protect fresh patches from rain and from foot traffic.
7. Recheck before the pour, especially areas walked on or disturbed by other trades after patching.

Cut ends. Every sheared or sawn end is bare steel and must be patched. Plan cuts into the shop bar list wherever possible, because shop patching under controlled conditions is easier to do well than patching on a cold, wet deck.

Preventing damage in the first place

Most touch-up is avoidable. The practices below come from RSIC guidance for epoxy-coated bar:

• Lift with nylon slings, not chains or wire rope, and avoid excessive sag in the bundles.
• Do not drag bars, and store them on non-metallic supports, off the ground, until placing.
• Store under cover and protect from the elements and sunlight.
• Use non-metallic or coated chairs, supports and tie wire.
• Use plastic-tipped vibrators, which most specifiers require on coated bar.
• Keep heavy traffic off the mat. Lay runways for buggies and pump lines rather than running them over coated bar.

Exposed rebar in existing concrete is a different job

Some searches for "epoxy coating for exposed rebar" are about something else: plain rebar showing through spalled or damaged concrete on an existing structure. Touch-up patching material for new coated bar is not the fix for that.

Repairing exposed rebar in old concrete involves removing the damaged concrete, cleaning the corroded bar, assessing whether it has lost section, applying the protective coating specified by the repair system, and rebuilding the cover with a repair mortar or concrete. Where the bar carries load, an engineer should assess it. Our guide on how to cover and repair exposed rebar walks through that process.

Corrosion-resistant bar for your next job

Touch-up is the weak point of any coated bar, which is one reason designers also consider other corrosion-resistant options. Our comparisons of galvanized vs epoxy-coated rebar and GFRP vs steel rebar set out the trade-offs.

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