FINISH PRIMER 442

What is FINISH PRIMER 442 and why choose it?

FINISH PRIMER 442 by Alexseal is an epoxy-based finish primer designed for professional use on marine and industrial surfaces. It delivers advanced adhesion on a wide range of substrates, excellent sanding characteristics, mechanical resistance and a good film build. Used as a base under ALEXSEAL topcoats, it enhances the desired “wet look” finish and can be applied both above and below the waterline (with an additional water barrier primer required below the waterline before antifouling).

Main features

• Epoxy finish primer with high adhesion on gelcoat, fiberglass, steel, aluminium (over appropriate metal primer) and existing coatings.
• Excellent sanding and film-building properties for smooth, fair surfaces and high-quality topcoat appearance.
• Versatile use: suitable for new builds, refits and repairs, and for sealing Alexseal fillers and primers.
• Above and below waterline application; below the waterline it must be followed by a water barrier primer before antifouling.
• Available colors: white or gray base with clear converter to match different build and inspection needs.
• Consistent coverage with 39% volume solids (catalyzed without reduction) and recommended dry film thickness of 75–100 µm (3–4 mils).
• Flexible application methods: spray (conventional or HVLP), brush and roller with defined nozzle sizes and pressures.
• Adjustable viscosity with 15–25% reduction and optional slow reducer for higher temperatures or roller work.
• Optional accelerator (A4429) to significantly shorten drying times where permitted by the system design.
• Professional performance window with clear pot life, recoat and overcoat times for controlled workflows.

Key technical specifications

• Product type: Epoxy-based finish primer
• Intended use: Industrial serial painting; marine priming and sealing of stable prepared substrates
• Colors of mixture: White / Gray
• Base materials: White (P4420) / Gray (P4423)
• Converter: Clear (C4427)
• Volume solids (catalyzed, without reduction): 39%
• Recommended dry film thickness (DFT): 75–100 µm (3–4 mils)
• Theoretical coverage at 75–100 µm DFT:
  • 6.2 m²/liter
  • 23.5 m²/gal
  • 253 sq. ft./gal
• Practical coverage (typical):
  • Conventional air spray: 2.9 m²/l (11.2 m²/gal; 120 sq. ft./gal)
  • HVLP spray: 3.3 m²/l (12.5 m²/gal; 134 sq. ft./gal)
  • Brush/roller: 5.5 m²/l (20.9 m²/gal; 225 sq. ft./gal)
• Mixing ratio (by volume):
  • 1 part ALEXSEAL Finish Primer 442 Base (P4420 or P4423)
  • 1 part ALEXSEAL Finish Primer 442 Converter (C4427)
  • 15–25% R4042 ALEXSEAL Epoxy Primer Reducer (or suitable slow reducer as specified)
• Typical example mix: 1 : 1 : ½ (base : converter : reducer) = 25% reduction for spray application
• Viscosity (mixed):
  • Zahn #2: ≈ 25 s
  • DIN 4 cup 4 mm: ≈ 21 s
• Recommended wet film thickness (WFT) per coat: 100–200/220 µm (4–8 mils)
• Resulting DFT:
  • Approx. 50 µm (2 mils) after 2 coats (English TDS)
  • Minimum before sanding: 75 µm (3 mils) DFT
  • Maximum (spray): 3 coats, 300 µm (12 mils) WFT total, or 100 µm (4 mils) DFT
• Application equipment – nozzle sizes:
  • Gravity gun: 1.4–1.8 mm (0.055–0.071 in) – Conventional & HVLP
  • Siphon cup: 1.6 mm (0.060 in) – Conventional & HVLP
  • Pressure pot: 1.2–1.6 mm (0.046–0.060 in) – Conventional & HVLP
• Atomizing pressure: 2.0–4.0 bar (30–60 PSI) – Conventional & HVLP
• Pot pressure (pressure pot): 0.7–1.5 bar (10–22 PSI)
• Pot life (approx.): 12 hours at 15–30°C (60–85°F)
• Pot life with A4429 accelerator: 6 hours at 15–30°C (60–85°F)
• Dust free: 30–90 min depending on temperature (approx. 30 min at 30°C; 90 min at 15°C)
• Tape-dry (without accelerator): approx. 14–30 hours (temperature-dependent)
• Tape-dry (with A4429): approx. 12–24 hours
• Full cure (without accelerator): approx. 5–11 days (temperature-dependent)
• Recoat window with Finish Primer 442: minimum 1–3 hours; maximum 24 hours (depending on temperature)
• Overcoat window with other Alexseal products (e.g. 302, 303, 328 fairing compounds, topcoats): minimum 12 hours, maximum 24 hours; sanding required after maximum time and before topcoating.
• Recommended application environment: 15–30°C (60–85°F), 40–80% RH; minimum application temperature 3°C (5.4°F) above dew point.
• Physical properties (mixed product):
  • Physical state: liquid
  • Boiling range: approx. 120°C
  • Flash point: 10.5°C (ISO 13736)
  • Auto-ignition temperature: > 400°C
  • pH (10%): 6–8 at 20°C
  • Density: 1.49 g/cm³ at 20°C
  • Water solubility: insoluble; immiscible with water
  • Vapour pressure: approx. 100 hPa at 50°C

Applications and use cases

• Gelcoat and fiberglass hulls and superstructures: Apply directly after sanding with P100–P150 grit to prime and seal new or aged composite surfaces.
• Refit and repair of existing coatings: Use on old coatings that show good adhesion and chemical resistance, after sanding with P100–P150 and performing compatibility tests where the existing system is uncertain.
• Metal substrates (steel and aluminium): Use over ALEXSEAL Protective Primer 161 (metal primer) to build an epoxy finish priming system before fairing and topcoats.
• Fairing systems: Apply over ALEXSEAL Super Build 302 following block sanding with P100–P180 grit to seal and refine fairing before topcoats.
• Above-waterline topcoat base: Provides a smooth, stable base that improves the appearance and “wet look” of ALEXSEAL topcoats on topsides, decks, superstructures and components.
• Below-waterline epoxy build: May be used below the waterline as part of a multi-layer system; an additional water barrier primer is required before applying antifouling.
• Industrial serial painting: Suitable for controlled shop application where defined pot life and drying schedules are important.

FAQ – FINISH PRIMER 442

1. On which substrates can FINISH PRIMER 442 be used?

   It is designed for properly prepared, stable gelcoat and fiberglass, over Alexseal primers and filler systems, and over steel or aluminium that have first been coated with ALEXSEAL Protective Primer 161. It can also be used on sound, sanded existing coatings after a compatibility test.

2. Can it be used 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 over FINISH PRIMER 442 before any antifouling coating.

3. What is the recommended film thickness?

   Apply 2–3 coats at 100–200/220 µm (4–8 mils) WFT per coat. The recommended DFT is 75–100 µm (3–4 mils). Minimum DFT before sanding is 75 µm (3 mils); the maximum for spray application is 100 µm (4 mils) DFT in three coats.

4. How long can I use the mixed product (pot life)?

   Pot life is approximately 12 hours between 15°C and 30°C. When A4429 accelerator is added, pot life is reduced to about 6 hours.

5. When can I sand and overcoat?

   At typical conditions, the primer is dust-free within 30–90 minutes. Recoat with another coat of FINISH PRIMER 442 after 1–3 hours (minimum) and within 24 hours (maximum). Overcoating with other Alexseal products such as fairing compounds or topcoats is possible after a minimum of 12 hours and within 24 hours; sanding is required after the maximum interval and before topcoating.

6. Which reducers can I use and when is a slow reducer recommended?

   Standard reduction is 15–25% with R4042 ALEXSEAL Epoxy Primer Reducer. Slow reducers (R4032 or R5015 / R4043, depending on system) are recommended for roller applications or at temperatures above 20°C to avoid dry spray and to improve flow.

7. What is the role of A4429 Accelerator?

   A4429 ALEXSEAL Accelerator for Finish Primer 442 shortens drying times. Add up to 12.5% to the catalyzed primer (e.g. 2 quarts base + 2 quarts converter + 1 pint A4429). A4429 replaces an equivalent part of the reducer. Higher dosages are not recommended because they reduce pot life. When applying 442 directly on metal, use of A4429 is not recommended.

8. Why do crystals sometimes appear in the converter?

   The converter can occasionally form tiny crystals due to its physical properties. This crystallization is a natural process, not a sign of adulteration or spoilage, and does not negatively impact product quality.

9. What causes dry spray or pinholes and how can I avoid them?

   Dry spray may be caused by poor atomization, holding the spray gun too far from the surface, high air temperature, excessively fast solvent evaporation or windy conditions. Pinholes may result from entrapped solvents or incorrect application technique. Adjust spray settings, distance and environmental conditions; if defects occur, sand to a rough, even surface and recoat.

10. Is FINISH PRIMER 442 classified as hazardous?

    Yes. According to the Safety Data Sheet, it is a highly flammable liquid and vapour (Flam. Liq. 2, H225), causes skin irritation (H315), causes serious eye damage (H318), may cause an allergic skin reaction (H317), may cause drowsiness or dizziness (H336) and is toxic to aquatic life with long lasting effects (H411). Appropriate handling and personal protection are required.

Section 14 – Transport information

• UN number / ID number: UN 1263
• UN proper shipping name: PAINT (includes trizinc bis(orthophosphate), Fatty acids C18-unsatd. dimers, oligomeric reaction products with tall-oil fatty acids and triethylenetetramine)
• Transport hazard class: Class 3 (flammable liquids)
• Packing group: II
• ADR:
  • Classification code: F1
  • Hazard identification number: 33
  • Labels: 3
  • Tunnel restriction code: (D/E)
  • Environmentally hazardous: yes
  • Special provision: 640D
• IMDG:
  • Class: 3
  • Packing group: II
  • Labels: 3
  • EmS code: F-E, S-E
  • Marine pollutant: yes
• IATA (cargo aircraft):
  • Packing instruction: 364
  • Packing group: II
  • Labels: Flammable Liquids
• IATA (passenger aircraft):
  • Packing instruction: 353 (Y341 for limited quantities)
  • Packing group: II
  • Labels: Flammable Liquids
• Bulk transport according to IMO instruments: Not applicable for product as supplied.
• On-site transport advice: Always transport in closed, upright, secure containers. Ensure personnel know emergency procedures in case of incident or spillage.

Section 8 – Personal protective measures

According to the Safety Data Sheet, FINISH PRIMER 442 contains flammable solvents and components that can irritate skin and eyes, cause allergic skin reactions, and affect the central nervous system. Appropriate engineering controls and personal protective equipment (PPE) are essential.

Engineering controls

• Provide adequate ventilation, preferably using local exhaust and good general extraction.
• If ventilation alone does not maintain solvent vapour and spray mist below occupational exposure limits, suitable respiratory protection must be worn.

Eye and face protection

• Wear safety goggles to protect against solvent and paint splashes.

Hand protection

• Use chemical-resistant protective gloves tested according to EN 374.
• Recommended materials for short-term contact (splash protection): nitrile rubber or neoprene.
• Minimum material thickness: > 0.4 mm; breakthrough time: > 480 minutes.
• Always verify glove suitability for the specific workplace (mechanical resistance, product compatibility, antistatic properties).
• Follow glove manufacturer’s instructions for use, storage, care and replacement. Replace damaged or worn gloves immediately.
• Use protective skin creams as preventive care and wash any contaminated skin immediately.

Skin and body protection

• Wear suitable protective clothing, including antistatic garments where explosive atmospheres may occur.
• For painting and sanding operations, use clothing that covers exposed skin to minimize contact.

Respiratory protection

• If solvent concentrations exceed air limit values, wear a suitable breathing apparatus (e.g. half-mask with appropriate cartridges or air-fed respirator).
• Dry grinding, torch cutting or welding on coated surfaces can generate hazardous dust and vapours; use wet methods where possible and ensure extraction or respiratory protection.
• When personnel are present inside spray booths during application, a compressed air-fed respirator should be worn until particulate and solvent vapour levels fall below exposure limits.

General hygiene and safety measures

• No eating, drinking or smoking in the work area.
• Avoid contact with skin, eyes and clothing.
• Avoid inhalation of vapours, spray mist and dust from sanding.