FINISH PRIMER 442 CONVERTER

What is ALEXSEAL Finish Primer 442 Converter and why choose it

ALEXSEAL C4427 Finish Primer 442 Converter is the clear curing component of the ALEXSEAL Finish Primer 442 epoxy primer system. It is a mixture of synthetic resins and organic solvents that, when combined 1:1 with the Finish Primer 442 base, provides advanced adhesion on various substrates, high-quality film build and excellent sanding properties. Designed for professional industrial and marine painting, it is suitable for applications above and below the waterline when used as part of the complete Finish Primer 442 system.

Main features

• Dedicated converter for Finish Primer 442: Specifically formulated to react with ALEXSEAL Finish Primer 442 base for consistent curing and performance.
• Clear appearance: Converter is clear, allowing the final mixed colour to be defined by the white or grey base component.
• Optimised film build and sanding: In a 1:1 mix with base, the system delivers good film build with exceptional sanding characteristics and mechanical resistance.
• Professional coverage performance: Mixed and unreduced system offers 39% volume solids, supporting efficient coverage in both spray and brush/roller applications.
• Covers multiple substrates: Finish Primer 442 system is designed to prime and seal properly prepared gelcoat, fiberglass, fairing systems and other Alexseal primers.
• Supports the ALEXSEAL “Wet Look” topcoats: Used as a base, it enhances the visual “Wet Look” of ALEXSEAL topcoats.
• Controlled crystallisation behaviour: Due to its physical properties, the converter may form small crystals over time; this is a natural process and does not adversely affect quality.
• For professional use: Intended for industrial serial painting and professional yacht or vessel finishing applications.

Technical characteristics

System composition and colours

• Converter trade name: ALEXSEAL Finish Primer 442 Converter (C4427)
• Appearance: Clear
• Compatible bases: Finish Primer 442 White (P4420) and Finish Primer 442 Gray (P4423)
• Mixed system colours: White / Gray (depending on base)
• Chemical nature: Mixture of synthetic resins and organic solvents

Mixing and thinning

• Mixing ratio (by volume):
  • 1 part Finish Primer 442 Base (P4420 or P4423)
  • 1 part Finish Primer 442 Converter (C4427)
• Recommended reduction: 15–25% by volume with R4042 ALEXSEAL Epoxy Primer Reducer (typical example: 1 : 1 : 1/2 for spray application).
• Maximum reduction: Up to 25% for thin, smooth sealer-type applications where heavy surfacing build is not required.
• Slow reducer option: Slow Reducer may be used for roller applications or at higher temperatures (>20 °C).

Viscosity and application equipment

• Approximate mixed viscosity:
  • Zahn #2: ≈ 25 s
  • DIN 4 mm cup: ≈ 21 s
• Recommended nozzle sizes (Conventional & HVLP):
  • Gravity gun: 1.4–1.8 mm (0.055–0.071 in)
  • Siphon / general spray: 1.6 mm (0.060 in)
  • Pressure pot: 1.2–1.6 mm (0.046–0.060 in)
• Atomizing pressure: 2.0–4.0 bar (30–60 psi)
• Pressure pot pressure: 0.7–1.5 bar (10–22 psi)

Film thickness and coverage (mixed system)

• Volume solids (catalyzed without reduction): 39%
• Recommended dry film thickness (DFT): 75–100 µm (3–4 mils) per application cycle.
• Theoretical coverage at 75–100 µm DFT:
  • 6.2 m²/l
  • 23.5 m²/gal
  • 253 ft²/gal
• Practical coverage (typical values at 75–100 µm DFT):
  • Conventional air spray: 2.9 m²/l (11.2 m²/gal; 120 ft²/gal)
  • HVLP: 3.3 m²/l (12.5 m²/gal; 134 ft²/gal)
  • Brush/roller: 5.5 m²/l (20.9 m²/gal; 225 ft²/gal)
• Wet film thickness (WFT) per coat: 100–200/220 µm (4–8 mils)
• Typical DFT:
  • 2 coats: approx. 50–75 µm (2–3 mils)
  • Minimum DFT before sanding: 75 µm (3 mils)
  • Maximum DFT by spray (3 coats): 100 µm (4 mils), 300 µm (12 mils) WFT total

Pot life and drying of the mixed system

Optimal application environment range: 15–30 °C (60–85 °F), 40–80% relative humidity.

• Approximate pot life (without accelerator): 12 h at 15–30 °C
• Approximate pot life with A4429 Accelerator: 6 h at 15–30 °C
• Dust-free time:
  • 15 °C: 90 min
  • 20 °C: 60 min
  • 25 °C: 45 min
  • 30 °C: 30 min
• Tape dry (without accelerator): approx. 30 h (15 °C), 24 h (20 °C), 18 h (25 °C), 14 h (30 °C)
• Tape dry (with A4429 Accelerator): approx. 24 h (15 °C), 18 h (20 °C), 14 h (25 °C), 12 h (30 °C)
• Fully cured (without accelerator): approx. 11 days (15 °C), 9 days (20 °C), 7 days (25 °C), 5 days (30 °C)
• Recoat window with Finish Primer 442:
  • Minimum: 3 h at 15 °C; 2 h at 20 °C; 1 h at 25–30 °C
  • Maximum: 24 h
• Overcoat window with other products (e.g. fairing compounds 302, 303, 328):
  • Minimum: 12 h at 15–30 °C
  • Maximum: 24 h (sanding required after maximum time and before topcoating)
• Minimum substrate temperature during drying: 15 °C (60 °F)
• Ideal application temperature: approx. 25 °C (77 °F)
• Dew point rule: Application conditions should be at least 3 °C (5.4 °F) above dew point.

Physical data (converter)

• Physical state: Liquid (20–25 °C, 1,013 hPa)
• Odour: Characteristic
• Boiling point: ca. 120 °C
• Flash point: 11 °C (ISO 13736)
• Upper explosion limit: 10% (v/v)
• Lower explosion limit: 1% (v/v)
• Auto-ignition temperature: > 400 °C
• pH (10% in water, 20 °C): 5–7
• Kinematic viscosity: > 21 mm²/s
• Density: 0.97 g/cm³ (20 °C)
• Water solubility: Insoluble (immiscible with water)

Applications and use cases

The C4427 Converter is not used alone; it is always combined with the Finish Primer 442 base to form a high-performance epoxy primer. Typical professional applications include:

• Yacht and boat finishing: Priming and sealing of gelcoat and fiberglass hulls and superstructures to provide a smooth, sandable base for ALEXSEAL topcoats.
• Refit and repair work: Over properly prepared, stable old coatings with sufficient adhesion and chemical resistance after sanding with P100–P150 grit.
• Fairing systems: Applied over ALEXSEAL Super Build 302 after block sanding with P100–P180 grit to refine the surface before topcoating.
• Use above and below waterline: As part of the Finish Primer 442 system, can be used above and below the waterline. Below the waterline, an additional water barrier primer must be applied before antifouling.
• Industrial serial painting: Intended for professional industrial coating processes where controlled curing and consistent film build are required.

FAQ – ALEXSEAL Finish Primer 442 Converter

Is the converter used on its own?

No. C4427 Finish Primer 442 Converter must always be mixed 1:1 by volume with ALEXSEAL Finish Primer 442 base (white or grey) before application.

What reducer should be used with the mixed primer?

Use R4042 ALEXSEAL Epoxy Primer Reducer at 15–25% by volume. A slow reducer can be used for roller application or higher temperatures (>20 °C).

What happens if crystals form in the converter?

The converter can form small crystals due to its physical properties. This crystallisation is a natural process and is not a sign of spoilage or quality loss.

What is the pot life after mixing base and converter?

Approximate pot life is 12 hours at 15–30 °C without accelerator and about 6 hours when A4429 Accelerator is used.

Can the Finish Primer 442 system be sanded?

Yes. The system offers exceptional sanding properties. The minimum recommended dry film thickness before sanding is 75 µm (3 mils).

What should I do if I see dry spray or pinholes?

Dry spray can be caused by poor atomisation, excessive gun distance, high air temperature, fast solvent evaporation or windy conditions. Sand back to a rough, even surface and recoat. Pinholes may result from trapped solvents or incorrect application technique and must be sanded and recoated.

Is the product flammable?

Yes. The converter is classified as a highly flammable liquid (flash point 11 °C). Keep away from heat, hot surfaces, sparks and open flames and observe all safety instructions.

Is the mixed system suitable below the waterline?

Yes, Finish Primer 442 may be used above and below the waterline; below the waterline, a separate water barrier primer must be applied before antifouling.

Is this product intended for DIY users?

No. All documentation specifies “Professional Use Only”; it is designed for trained professional applicators.

Section 14 – Transport information

• UN number: UN 1263
• UN proper shipping name: PAINT RELATED MATERIAL
• Transport hazard class: Class 3 (flammable liquids)
• Packing group: II
• ADR details:
  • Classification code: F1
  • Hazard identification number: 33
  • Labels: 3
  • Tunnel restriction code: (D/E)
  • Special provision: 640D
• IMDG details:
  • Packing group: II
  • Labels: 3
  • EmS code: F-E, S-E
  • Marine pollutant: No
• IATA details (air transport):
  • Cargo aircraft packing instruction: 364; Packing group II; Labels: Flammable Liquids
  • Passenger aircraft packing instruction: 353; Limited Quantity instruction: Y341; Packing group II; Labels: Flammable Liquids
• On-site transport advice: Within the user’s premises, always transport in closed, upright and secure containers. Ensure persons handling the product know the procedures in case of incident or spill.

Section 8 – Personal protective measures

The converter and the mixed Finish Primer 442 system contain organic solvents and epoxy resins that can cause skin and eye irritation, allergic skin reactions, drowsiness or dizziness and organ damage after prolonged or repeated exposure. Appropriate engineering controls and personal protective equipment (PPE) are essential.

Engineering controls

• Provide good general ventilation; where possible, use local exhaust extraction at mixing and application areas.
• If ventilation cannot maintain vapour and aerosol concentrations below the applicable exposure limits, suitable respiratory protection must be worn.

Eye and face protection

• Wear safety goggles designed to protect against solvent splashes.

Hand protection

• Use chemical-resistant protective gloves certified to EN 374.
• Recommended materials for short-term contact (splash protection): nitrile rubber or neoprene.
• Minimum material thickness: > 0.4 mm; breakthrough time: > 480 min (under test conditions).
• Check glove suitability for the specific workplace (mechanical resistance, product compatibility, antistatic properties).
• Replace gloves immediately if damaged or showing signs of wear. Wash contaminated skin promptly and use preventive skin protection creams.

Skin and body protection

• Wear suitable protective clothing; for operations where explosive atmospheres may occur, anti-static protective clothing is required.

Respiratory protection

• If solvent vapour concentrations exceed occupational exposure limits, wear an approved breathing apparatus.
• Use at least a half-mask with appropriate combined filter or air-fed respirator.
• During spraying inside spray booths, compressed air-fed respirators are recommended until solvent vapour and particulate concentrations fall below exposure limits.
• Dry sanding, cutting or welding on coated surfaces can generate hazardous dust or vapours; prefer wet methods and/or use suitable respiratory PPE and extraction.

General protective measures and safe handling

• Do not eat, drink or smoke while handling this product.
• Avoid contact with skin, eyes and clothing.
• Do not breathe vapours, spray mist or sanding dust.
• Keep away from heat, hot surfaces, sparks, open flames and other ignition sources.
• Ensure containers are properly grounded during transfer to avoid electrostatic discharge; use only non-sparking tools.