What this industry manufactures
Cooling tower fabricators in India build packaged bottle-shaped and rectangular units for chiller plants and process cooling, and the FRP parts of larger field-erected induced-draft towers. The FRP content is the casing and shell panels, fan stacks and fan cylinders, louvres and air-inlet screens, cold-water basin sections, internal partitions and covers, and moulded fittings. Fill packs and drift eliminators are normally thermoformed PVC rather than laminate, and the fan, gearbox and motor are bought in — so the resin decision covers the structure and the enclosure, not the whole machine.
What each component asks of the resin
The parts of a tower do not make the same demand. Rheology decides how well a part can be laminated; chemistry decides how it lives afterwards.
- Casing and shell panels
- Large, mostly vertical or steeply curved mould faces. A resin that drains before it gels leaves the top of the panel resin-starved and the bottom heavy — this is the sag problem a thixotropic grade exists to solve.
- Fan stack / fan cylinder
- A deep section with vertical walls and a stiff throat, usually built up in stages. Working window and consolidation matter more here than gel speed.
- Cold-water basin and sumps
- Continuously wetted, and the first place treatment chemicals concentrate. Chemistry, not rheology, is the deciding property; this is where the isophthalic grade earns its place.
- Louvres and air-inlet screens
- Thin, repeated profiles pulled from dedicated moulds. Consistency between mouldings and clean release matter most.
- Internal partitions, decks and covers
- Warm, saturated air on both faces, with access for inspection and repair usually limited once the tower is assembled.
- Structural members, ladders and handrails
- Often pultruded profiles rather than hand-laid sections. That is a different process with its own grade — the catalogue lists SPR 401 PT for continuous pultrusion.
Why FRP, and what that asks of the resin
A cooling tower laminate is built the way most FRP is built — glass reinforcement wetted out with a polyester resin and cured at room temperature with MEKP and a cobalt accelerator added separately — so the resin has to wet out evenly across panel-sized areas and hold a working window long enough to finish the panel. What separates the cooling-tower grades from a general laminating resin is rheology: SPR 201 CTG and SPR 301 CT are both thixotropic, so they thin while they are being rolled into the glass and recover their body at rest instead of draining down a vertical face.
The second decision is chemistry. Orthophthalic polyester is the general-purpose family and is widely used for tower casings and enclosure parts. The catalogue specifies its isophthalic SPR 301 family where a laminate faces water immersion, chemical service or sustained outdoor conditions, and describes SPR 301 CT as a thixotropic isophthalic grade with heat, chemical and corrosion resistance and high strength — which is why basins and parts in hot or heavily dosed water point that way. Neither grade publishes a chemical-resistance chart or a service-temperature limit, so the circulating-water conditions belong in the enquiry rather than in an assumption.
What the laminate lives in
Share as many of these as you know when you ask for a recommendation — they decide the answer more than the part name does.
- Constant wetting
- Circulating water films both faces of most internal parts, and the structure rarely dries out fully in service.
- Water temperature
- Hot water returns from the process to the distribution system; how hot depends entirely on the plant, and no grade here publishes a temperature limit.
- Treatment chemistry
- Biocides, chlorine or bromine donors, acid dosing for pH control, scale and corrosion inhibitors. Concentration, pH and dosing regime matter more than the chemical names.
- Weather on the outside
- Sunlight, rain and daily thermal cycling on the outer shell, which is what the gelcoat is there to take.
- Mechanical loading
- Fan vibration, wind load on a tall casing, water load in a full basin, and the bolting stresses of site assembly.
- Cleaning and shutdown
- Periodic chemical cleaning, and dry-out during shutdown, are part of the service the laminate sees.
Required resin characteristics
- 01Sag resistance on vertical and steeply curved mould faces, so a panel keeps its designed thickness from top to bottom
- 02A working window that matches the panel size and the shop temperature, not just the datasheet figure
- 03Even wet-out of chopped strand mat and any woven reinforcement, with no dry patches at ribs and edges
- 04Chemistry matched to the circulating water the finished part will see, decided part by part
- 05Batch-to-batch consistency, so laminate thickness and stiffness do not drift across the many panels of one tower
- 06A surface system — gelcoat and cure — that holds up to sunlight and water on the outside of the shell
Grade selection for cooling tower work
Published typical values, each from the product named in its column. They describe the liquid resin at its reference condition, not a finished tower, and none of these grades is the right answer for every part.
| Orthophthalic Cooling Tower Grade Resin (SPR 201 CTG) | Isophthalic Cooling Tower Grade Resin (SPR 301 CT) | GP Yellow Resin | Vinyl Ester Resin | |
|---|---|---|---|---|
| Chemistry | Orthophthalic unsaturated polyester | Isophthalic unsaturated polyester | Orthophthalic unsaturated polyester | Bisphenol-A epoxy vinyl ester |
| Rheology | Thixotropic | Thixotropic, index 2.0–3.5 | Not listed as thixotropic | Not listed as thixotropic |
| Viscosity (typical) | 350–450 cPs | 400–650 cPs at 60 rpm; 1,500–2,000 cPs at 6–12 rpm | 450–600 cPs @ 25°C | 350 cPs (at 25°C) |
| Gel time (typical) | Under 8 minutes | 15–35 minutes at 25 °C | 10–15 minutes | 15–20 minutes at 25°C |
| Styrene content (typical) | 33–40% | 37–45% by weight | 34–38% | 40% |
| Where it fits on a tower | Casings, shells and other parts laid up on large vertical faces, in ordinary treated water | The same parts where the water is hot, heavily dosed or corrosive, and basins in continuous contact | General panel and moulded work in a shop already running this grade | Parts in the most aggressive circulating-water chemistry, or where a specification names vinyl ester |
Values are typical, from the 2026 product catalogue (SPR 201 CTG, SPR 301 CT) and each other product’s own technical data sheet. Viscosities measured at different spindle speeds are not directly comparable. No grade here publishes a chemical-resistance chart or a service-temperature limit.
View SPR 201 CTGView SPR 301 CTView GP Yellow ResinView Vinyl Ester Resin
Manufacturing process
Casing panels, fan stacks and basin sections are laminated by hand lay-up — and, in shops set up for it, spray-up — over flat, curved or deep moulds. Chopped strand mat is placed and wetted out with resin catalysed by MEKP and accelerated with cobalt octoate, each added to the resin separately, with extra layers and ribs built in where a panel needs stiffness. Louvres and smaller mouldings are pulled from dedicated tools for profile consistency. Panels are cured at room temperature, trimmed and drilled, then bolted or bonded into the tower on site.
Process notes worth settling on the shop floor
- Stage thickness on a vertical face is the real test of a thixotropic grade — trial the heaviest stage you intend to lay in one pass, on the actual mould angle.
- The reference cure for both cooling-tower grades is MEKP 1.5% with cobalt octoate 0.4%, added separately. That is the catalogue’s measuring condition; the production dosage follows from shop temperature and panel size, established in trials.
- Never mix a concentrated peroxide initiator directly with a cobalt accelerator. Each goes into the resin on its own.
- SPR 201 CTG gels in under 8 minutes typical and SPR 301 CT in 15–35 minutes at 25 °C, so the two grades suit different panel sizes and shift patterns.
- Moulds for repeated panel production are their own project: the catalogue lists SPR 401 TL for composite mould and tooling work.
Surface and gelcoat
The gelcoat is the face of the tower — the surface that meets sunlight, rain and cleaning, and the surface an inspector sees first. It is applied to the mould before the laminate, so it has to be decided with the laminate, not after it.
GP Gelcoat Resin is the general-purpose white, high-gloss, thixotropic surface coat, cured with MEKP at 1.5%. ISO Gelcoat is the isophthalic grade the catalogue positions where a surface has to hold gloss and colour through weathering and water contact, and it is the one with published weathering data: ISO 4892-2 xenon arc, 1,000 hours, ΔE 3–5 with 80% gloss retention. Colour, film thickness and the back-up laminating window all belong in the trial.
Advantages
- Two grades listed for cooling-tower work — orthophthalic SPR 201 CTG and isophthalic SPR 301 CT — so the choice can follow the part rather than one house resin
- Both are supplied non-accelerated, leaving the fabricator to set dosage against shop temperature and panel size
- Thixotropic rheology aimed squarely at the vertical lay-up that cooling-tower panels demand
- Manufactured at Doraha, Punjab, with the same technical team available for grade selection, trials and batch questions
Common products produced
- FRP cooling tower casing and shell panels
- Fan stacks and fan cylinders
- Louvres and air-inlet screens
- Cold-water basin sections and sumps
- Internal partitions, decks and covers
- Moulded fittings and enclosure parts
Questions to answer before you choose a grade
A fabricator who can answer these gets a specific recommendation instead of a generic one.
- 01Which part is being laminated, and at what angle is the mould face?
- 02What laminate schedule and stage thickness does the panel need?
- 03What is the shop temperature range across the year, and how long is a panel’s lay-up?
- 04How hot is the circulating water in service, and what is dosed into it — biocide, chlorine or bromine, acid, inhibitors?
- 05Is the part continuously immersed, splashed, or only in saturated air?
- 06Does a customer or consultant specification name a resin family, a gelcoat or a fire requirement?
- 07What surface finish and colour does the finished tower need?
- 08What volumes, packaging and delivery location should the quotation cover?
When to consider a different resin
Vinyl Ester Resin (SPR 501 VE)
Where the circulating water is aggressive enough that an isophthalic polyester is not the right answer, or where the specification names vinyl ester. Its published applications include cooling towers.
ISO Polyester Resin (SPR 301)
The general isophthalic grade — not thixotropic, but the one with published cured-resin data, for parts where that data is wanted and sag is not the problem.
Fire-retardant grades
Where a fire requirement is specified for the tower. No fire classification is published for any grade; a classification belongs to a tested construction.
Pultrusion Grade Resin (SPR 401 PT)
For structural profiles pulled through a heated die rather than laminated — a different process with a heat-activated cure.
GP Clear Resin (SPR 201 GPC)
The general-purpose clear laminating grade, whose published applications include cooling tower components, for shops standardised on it.
Frequently asked questions
A general-purpose or isophthalic unsaturated polyester, cured at room temperature with MEKP and cobalt octoate. Samrat Poly Resins lists two grades specifically for the work: the thixotropic orthophthalic SPR 201 CTG and the thixotropic isophthalic SPR 301 CT. Which one suits a given part depends on the lay-up and on the circulating water.
Orthophthalic grades are the general-purpose family and are widely used for casings and enclosure parts. The catalogue specifies its isophthalic family where a laminate faces water immersion, chemical service or sustained outdoor conditions, so basins and parts in hot or heavily dosed water usually point to SPR 301 CT. Share the water temperature and treatment programme and the technical team will recommend a grade to trial.
Casings and fan stacks are laid up on vertical and steeply curved faces. A thixotropic resin thins while it is being rolled into the reinforcement and recovers its body at rest, so it stays where it was placed instead of draining before it gels. That is what keeps panel thickness consistent from top to bottom.
No service-temperature limit is published for SPR 201 CTG or SPR 301 CT, so none is claimed here. The catalogue describes SPR 301 CT as a thixotropic isophthalic grade with heat, chemical and corrosion resistance; the actual operating temperature and water chemistry should be shared for review before a grade is selected.
No chemical-resistance chart is published for either grade, and resistance depends on the chemical, its concentration, the pH and the temperature. Tell us what is dosed into the circulating water and how, and the suitability can be reviewed for that service — including whether vinyl ester is the better route.
GP Gelcoat Resin is the general-purpose white, high-gloss, thixotropic surface coat. ISO Gelcoat is the isophthalic grade positioned for surfaces that must hold gloss and colour through weathering and water contact, and it publishes weathering data — ISO 4892-2 xenon arc, 1,000 hours, ΔE 3–5 with 80% gloss retention.
Fill packs and drift eliminators are normally thermoformed PVC rather than laminate, and the fan, gearbox and motor are bought-in equipment. The resin decision covers the casing, fan stack, louvres, basin sections, partitions and moulded fittings.
Panels are typically laminated with E-glass chopped strand mat, with extra layers at ribs and edges for stiffness. Samrat Poly Resins supplies chopped strand mat alongside the resin range, so the laminate can be quoted as one package.
Manufacturer context
Manufacturing and quality information
Manufactured at Doraha, PunjabThe grades on this page are produced at Samrat Poly Resins’ own plant; the company page describes the facility and its background.
Batch checks before despatchOur company information describes the checks for viscosity, gel time and cure behaviour made before a batch is approved.Discuss resin for your cooling tower production
Share the component, the mould, the laminate schedule and the circulating-water conditions, with your quantity and delivery location. The technical team will recommend a grade to trial and quote it in bulk.