At a glance
- The whole job lives or dies on two things: a sound, dry substrate (pull-off ≥ 1.5 MPa, moisture < 4%) and full wet-out — roll every air pocket out of the fabric before the resin gels.
- Six steps: prepare and test the surface, prime, level where needed, saturate and lay the first ply, add plies wet-on-wet, then cure, inspect, and protect.
- Plan the resin for the whole bay before you start — resin that gels mid-job cannot be rescued by a later top-coat; that section must be cut out.
Installing carbon fiber fabric is a wet lay-up: you bond a dry carbon weave to prepared concrete with a structural epoxy, on site, ply by ply. Done right it develops the fabric’s full capacity; done wrong it debonds before the fiber does any work. This is the FidStrong method, with every figure traced to the product data sheets and ACI SPEC-440.12-22, the mandatory field-QC standard. For what the system achieves, start with what CFRP strengthening is.
1. Prepare and test the surface
Everything starts with the substrate. Grind or abrasive-blast away all unsound concrete, laitance, paint, and contaminants until the aggregate is exposed and the profile is open. Then verify two numbers before any resin goes on: pull-off tensile strength must reach at least 1.5 MPa per the FidStrong data sheet (ACI’s code floor is 1.4 MPa / 200 psi, ASTM C1583), and moisture content must be below 4% (ASTM D4263). Round outside corners the fabric will wrap to a radius of at least 20 mm so the fiber is not kinked, and work only within a substrate and ambient temperature of +5 to +35 °C. Deep-dive: surface preparation for CFRP.
2. Prime the concrete
Prime to seal the pores and stop outgassing that would otherwise blister the laminate. Mix FSE302 primer at 2:1 by weight (about 40 minutes of pot life at 23 °C) and apply a single coat at 0.3–0.5 kg/m², worked into the surface with no puddling. It is tack-free in roughly 2 hours. Critically, the saturating resin must go on within the primer’s 2–24 hour recoat window — never after it has fully cured, or bond suffers.
3. Level any unevenness
Only where needed. Surface deviations greater than about 1 mm (fabric systems) are filled with FSE502 leveling putty (2:1 mix, touch-dry ~1.5 h, full cure ≥ 24 h) before priming, and deep repairs over 5 mm are built up in layers. The goal is a plane surface so the fabric beds down in full contact — bridging a gap leaves an unbonded void.
4. Saturate and lay the first ply
Apply a base coat of saturating resin at 0.3–0.4 kg/m² — FSE322 (2:1, ~70 min pot life) for general work, or FSE323H for overhead and heavy fabric that must not sag. Press the fabric into the wet resin along the design direction, holding orientation to within ±5° (ACI SPEC-440.12-22). Then apply a second coat through the fabric — from 0.5–0.7 kg/m² for 200 g/m² fabric up to 1.0–1.2 kg/m² for 600 g/m² — and roll from the centre outward with a ribbed roller to drive out every air bubble before the resin gels. This wet-out is the make-or-break quality point.
5. Add plies wet-on-wet
For multi-ply laminates, lay each additional ply while the previous layer is still tacky. If a layer is allowed to fully cure first, it must be mechanically abraded and solvent-wiped before the next ply can bond — a cured surface is not a valid substrate on its own. Overlap splices in the fiber direction by at least 100 mm (a data-sheet floor; the design lap length is set by testing per ACI 440.2R).
6. Cure, inspect, and protect
Let the laminate reach full cure — 7 days at 23 °C, protected from disturbance, rain, and sunlight (see curing guidelines). Then inspect: sound the surface by tap or coin test, or use infrared thermography, to find dry or delaminated spots, and on bond-critical jobs pull-off test to ASTM D7522 — a pass needs both > 200 psi (1.4 MPa) and failure inside the concrete. Finally, outdoors, protect against UV by broadcasting 0.5–1.0 mm of quartz sand into the last wet coat plus a compatible topcoat; cured epoxy left UV-exposed degrades.
FAQ
Do I need a primer, or can I apply resin straight to the concrete?
Prime first. FSE302 penetrates the concrete’s open pores and eliminates the outgassing that would otherwise blister the laminate. It must be applied and touch-dry (about 2 hours at 23 °C) before the saturating resin goes on, within its 2–24 hour recoat window.
How long does a wet-lay-up CFRP wrap take to fully cure?
FidStrong’s FSE322/FSE323 saturating resins reach full cure in 7 days at 23 °C. The laminate must stay undisturbed, dry, and shielded from sunlight for that period; lower temperatures extend the cure, so cold-weather installs need a longer protected window.
How is a finished installation checked for quality?
Two checks: sounding (tap/coin test or infrared) to find dry or delaminated spots, and pull-off testing to ASTM D7522 — at least 3 tests per 1,000 ft² and 3 per day, passing only if strength exceeds 200 psi (1.4 MPa) and failure occurs inside the concrete, not at the bond line.
What happens if a small bubble or delaminated spot is found after cure?
Size decides the fix. Under about 2 in² (13 cm²) is often left if total voids stay below 5% of the laminate; 2–25 in² gets low-pressure epoxy injection; anything 25 in² (160 cm²) or larger is cut out and patched with an engineer-approved overlap.
Why must resin that ran out mid-job be scrapped instead of topped up later?
Once resin under the fabric gels, a fresh coat hours later only films the surface — it cannot re-penetrate fibers already locked dry, leaving a weak cold joint. The fix is cutting out and re-laying that section, which is why you plan resin for the whole area first. See common installation mistakes.
FidStrong manufactures FSC carbon fiber fabric and the matching FSE primer, saturating, and leveling epoxies, under ISO 9001, 14001, and 45001 quality systems. Figures here are drawn from the product data sheets, ACI 440.2R, and ACI SPEC-440.12-22; installation must follow the project specification and a qualified engineer’s design.