At a glance
- Never apply below +5°C (substrate and air), up to +35°C, and never on standing water — the hard window on every FidStrong structural-epoxy data sheet. ACI 440.2R bars cold or frozen surfaces outright.
- Full cure takes 7 days (at 23°C per the resin data sheets), and temperature drives the speed — the FSE362 plate adhesive’s pot life runs 150 min at 10°C but only 40 min at 30°C.
- Substrate moisture must be <4% (ASTM D4263) for the bonded system; vapour migrating through uncured resin blisters the laminate and destroys the bond (ACI 440.2R-23 §6.2).
A CFRP laminate is only as good as its cure, and three conditions control it — temperature, moisture, and time — each with hard limits that decide whether the bond develops or fails. This guide sets out the temperature window, the moisture and dew-point rules, cure and pot-life times, and how the cured bond is verified, grounded in FidStrong data sheets and ACI 440.2R / ACI SPEC-440.12-22. For the steps around it, see how to install carbon fiber fabric.
What is the temperature window for applying and curing?
Both the substrate and the ambient air must be between +5°C and +35°C throughout application and cure — that is the stated window on every FidStrong FSE structural epoxy (primer FSE302, saturating epoxy FSE322/323, plate adhesive FSE362). ACI 440.2R Sec. 6.2 separately prohibits applying primer or resin to cold or frozen surfaces. Below +5°C the cure stalls; this is a hard floor, not a “just wait longer” situation. The knowledge base documents no heat-tenting or accelerated post-cure procedure for wet-layup CFRP, so do not improvise one — if it is too cold, reschedule or provide compliant enclosure heating per the manufacturer.
How does temperature change the cure speed?
Strongly. Warmer resin gels and cures faster; colder resin slows down. The clearest example is the FSE362 plate adhesive, whose working (pot) life runs 150 min at 10°C, 50 min at 23°C, and 40 min at 30°C. Plan mixing batch sizes and open time around the day’s temperature: a hot afternoon can halve your working window. (Anchoring adhesives in the same resin family show the same trend even more sharply.)
| Stage (at 23°C) | Primer FSE302 | Saturating epoxy FSE322 | Plate adhesive FSE362 |
|---|---|---|---|
| Pot life (500 g) | 40 min | 70 min | 50 min |
| Tack-free | 2 h | 1.5 h | — |
| Full cure | 7 days | 7 days | 7 days |
Can you apply on damp concrete, or in the rain?
Never on standing water or in rain. For the full bonded system, substrate moisture must be under 4% (ASTM D4263); the primer alone can go onto a damp (not wet) surface. ACI SPEC-440.12-22 §3.2.2 also requires air and substrate temperature to stay above the dew point during installation, and ACI 440.2R-23 §6.2 warns that moisture vapour migrating through the uncured resin surfaces as blisters and destroys the bond. Where the substrate is marginal, use a moisture-tolerant primer and check moisture per ASTM D4263 before committing resin. Note there is no published numeric dew-point margin in the guidance — the rule is simply “above the dew point.”
How long before the CFRP can carry load?
Full mechanical cure is 7 days at 23°C per the resin data sheets (fabric-system notes cite 7 days at 20°C — same order, different reference temperature). Do not confuse tack-free time with cure: the surface is dry to touch in 1.5–2 h, but the bond is nowhere near full strength then. Load only after full cure — FidStrong’s pre-cured CFRP anchor instructions are explicit that load is applied only once the injected adhesive is fully cured. One sequencing rule: structural adhesive must go on within the primer’s 2–24 h recoat window at 23°C — after the primer is tack-free but before it fully cures, never over a fully cured primer.
How is the cured bond verified — and what comes after?
Two things close out a cure. Verification: a field pull-off test (ASTM D7522) must exceed 200 psi (1.4 MPa) and fail within the concrete substrate, at 3 tests per 1,000 ft² and a minimum of 3 per day (ACI SPEC-440.12-22 §3.5.2); if specified, witness panels cure under the same conditions for at least 48 h before tensile testing. Protection: cured CFRP must never be left exposed to UV — broadcast quartz sand into the last wet coat and apply a UV topcoat or cementitious render. Skip prep or cure control and the pull-off fails in the resin or at the interface instead of the concrete; see common installation mistakes and surface preparation.
FAQ
What is the minimum temperature to apply and cure CFRP epoxy?
+5°C for both the substrate and the ambient air (up to +35°C) — the stated window on every FidStrong FSE epoxy data sheet. ACI 440.2R Sec. 6.2 separately bars application on cold or frozen surfaces. Below +5°C the cure stalls; warm the space or reschedule rather than apply.
Can I apply on damp concrete or in the rain?
Never on standing water or in rain. The full bonded system needs substrate moisture below 4% (ASTM D4263); the primer alone can go on a damp (not wet) surface. Air and substrate must also stay above the dew point (ACI SPEC-440.12-22 §3.2.2), and moisture vapour through uncured resin causes blistering that destroys the bond.
How long before the CFRP can carry load?
Seven days for full cure (at 23°C per the resin data sheets; fabric notes cite 20°C). Tack-free (1.5–2 h) is not cured — the bond is far from full strength then. Load only after full cure.
It’s cold on site — can I speed up the cure?
There is no documented heat-cure, tenting, or post-cure acceleration procedure for wet-layup CFRP in the guidance, so don’t improvise one. Temperature does drive cure speed (FSE362 pot life runs 150 min at 10°C down to 40 min at 30°C), but below +5°C you stop — that is a documented floor.
How is the bond verified after cure?
A field pull-off test (ASTM D7522) must exceed 200 psi (1.4 MPa) with failure inside the concrete substrate, at 3 tests per 1,000 ft² and at least 3 per day (ACI SPEC-440.12-22 §3.5.2). Witness panels, if specified, cure under the same conditions for at least 48 h before testing.
Does the finished laminate need protection?
Yes — cured CFRP must never be left exposed to UV. Broadcast quartz sand (0.5–1.0 mm) into the last wet coat and apply a UV topcoat or cementitious render; some plate adhesives also require a fire-rated or cementitious protective coating.
FidStrong manufactures the primer, saturating epoxy, and plate adhesive whose cure data appears above, under ISO 9001, 14001, and 45001 systems. Cure and QC rules follow the product data sheets and ACI 440.2R / ACI SPEC-440.12-22; the 7-day and temperature figures are reference-condition values — confirm the specific product’s data sheet and a qualified engineer’s requirements for your project.