Quick facts
- Grades compared
- SPR 201 FR-GC (orthophthalic) · SPR 401 FRGC (terephthalic)
- Role
- Mould-face surface layer of fire-retardant FRP parts
- Viscosity figures
- Measured at different conditions; not directly comparable
- Fire ratings
- None published; the finished part is tested
What differs
Both are thixotropic, non-accelerated fire-retardant gelcoats applied to the mould face before lay-up, so that a fire-retardant part carries a fire-retardant outer skin. SPR 201 FR-GC is orthophthalic; SPR 401 FRGC is terephthalic and is described with strong mechanical properties. Their published cures differ: SPR 201 FR-GC lists MEKP 1.5–2.0% as its reference cure, while SPR 401 FRGC lists MEKP 1.5% with cobalt octoate 0.4%, added separately.
They also differ in working window and make-up: a gel time of 9–16 minutes against 12–22 minutes at 25 °C, and styrene of 17–25% against 28–35% by weight.
How to decide
A fire-retardant gelcoat is chosen as part of a tested build-up, not on its own. If the project’s fire test was run, or will be run, on a laminate faced with one of these gelcoats, use that one. If the specification names a terephthalic surface or needs the listed white, grey or custom colours, SPR 401 FRGC fits; if the build-up is orthophthalic throughout, SPR 201 FR-GC is the family match. The catalogue pairs a fire-retardant gelcoat with the fire-retardant laminating resin of the same project.
Then check application: film thickness, spray or brush equipment and shop temperature all interact with thixotropy and gel time, so run a trial on the actual mould before production.
What the data does not tell you
The two grades publish viscosity at different measurement conditions: SPR 201 FR-GC as high-shear and low-shear readings at 25 °C, SPR 401 FRGC at 2 rpm and 20 rpm with a thixotropic index. The numbers are not directly comparable, so they cannot show which gelcoat sprays or holds on a vertical face better — only a trial can.
No fire rating, surface-spread class or smoke figure is published for either gelcoat. SPR 201 FR-GC gives specific gravity and SPR 401 FRGC gives density in g/cm³; both describe the liquid, not the cured film.
Sources, roles and the Nepal enquiry path
Both grades are described by the typical specification printed in the supplier’s 2026 product catalogue. No Technical Data Sheet for either gelcoat has been published on this site.
Samrat Poly Resins, India manufactures the grade and issues its technical information. Samrat FRP Traders is the Nepal supplier and importer and handles enquiries; price, packaging, lead time and stock in Nepal are confirmed on enquiry.
Two fire-retardant gelcoats side by side
| Criterion | SPR 201 FR-GC | SPR 401 FRGC |
|---|---|---|
| Chemistry | Orthophthalic fire-retardant gelcoat | Terephthalic fire-retardant gelcoat |
| Appearance and colour | Milky white to grey opaque liquid; custom-tinted variants where supplied | Opaque, thick pigmented liquid; white, grey or custom colour |
| Supply | Non-accelerated, thixotropic | Non-accelerated, thixotropic; thixotropic index 4.5–6.0 |
| Viscosity (as published) | High shear 5,000–11,000 cPs; low shear 30,000–45,000 cPs, at 25 °C | 12,000–18,000 cPs at 2 rpm; 2,000–3,500 cPs at 20 rpm |
| Gel time | 9–16 minutes at 25 °C | 12–22 minutes at 25 °C |
| Styrene · density | 17–25% by weight · SG 1.35–1.55 | 28–35% by weight · 1.25–1.45 g/cm³ |
| Reference cure | MEKP 1.5–2.0%, added during use | MEKP 1.5% + cobalt octoate 0.4%, added separately |
| Listed uses | Rail and metro composite parts; automotive FRP parts; surface gelcoat for fire-retardant laminates | Rail and transport composite parts; automotive composite parts; fire-retardant moulded FRP parts; described with strong mechanical properties |
| Choose when… | The project’s build-up is orthophthalic and its fire test was, or will be, run with this surface | The project specifies a terephthalic surface, needs the listed colour options, or its tested build-up uses this gelcoat |
Source: Samrat Poly Resins, India product catalogue, 2026 edition (typical specification) for both grades. The viscosity rows use different measurement conditions (high/low shear vs 2/20 rpm) and cannot be compared number for number. Typical values describe each grade; they are not batch guarantees or acceptance limits.
Frequently asked questions
Which gelcoat is thicker?
The published figures cannot say: one grade is measured at high and low shear, the other at 2 and 20 rpm. Compare them in a trial with your own equipment.
Why does SPR 201 FR-GC list no cobalt?
The catalogue’s reference cure for this grade is MEKP 1.5–2.0% only. Follow each grade’s own reference cure rather than carrying one over to the other.
Does a fire-retardant gelcoat make the part fire-rated?
No. It is one layer of the build-up. The finished part, with its laminate, has to be tested to the standard the project names.
Can I use a fire-retardant gelcoat over a standard laminate?
The catalogue pairs a fire-retardant gelcoat with a fire-retardant laminating resin. Whether another build-up meets a requirement is decided by testing that build-up.