Hempel Light Primer Epoxy Undercoat

Hempel’s Light Primer 45551 is a two-component, solvent-based epoxy primer and undercoat for glass fibre or GRP, steel, aluminium and plywood. Suitable above and below the waterline, it helps prevent osmotic blistering in glass fibre and protects marine substrates against general corrosion. Its theoretical coverage is 8.2m² per litre at a 60-micron dry film thickness.

Hempel’s Light Primer is suitable for interior and exterior marine applications and is particularly suited to the protection of keels and rudders. Hempel specifies three to five coats on uncoated surfaces below the waterline, two coats on uncoated surfaces above the waterline and one full undiluted coat on previously coated surfaces. Epoxy systems applied to aluminium must achieve a minimum total dry film thickness of 300 microns.

The system consists of Hempel’s Light Primer Base 45559 and Curing Agent 95360, mixed at a ratio of 2:1 by volume. Stir the base, add the curing agent and mix thoroughly, then allow the mixed coating to rest for several minutes so trapped air can escape. Apply by brush, roller, paint pad or airless spray. Use Hempel’s Thinner 845, product code 08451, for thinning and cleaning application tools.

All surfaces must be clean, dry and free from oil, grease, rust, loose material and other contamination. Uncoated surfaces should be sanded and dusted, while plywood should first be sealed with a suitable wood sealer. Steel should be abrasive-blasted or power-tool cleaned, and aluminium should be prepared with non-metallic blast media. Apply and cure only when the surface temperature is above 10°C and relative humidity is below 85%.

At 20°C, Hempel’s Light Primer is touch dry in approximately three hours, hard dry in six hours and fully cured in seven days. It is ready to sand after approximately 48 hours. The mixed product has a pot life of six hours for brush application or two hours for spray application at 20°C.

For an above-waterline Hempel’s Brilliant Gloss finish, use Light Primer as the epoxy foundation only where specified by the selected paint system. Hempel’s Primer Undercoat is the dedicated undercoat immediately before the single-component Brilliant Gloss topcoat. Follow the applicable system instructions and overcoating intervals for the substrate.

Key Features

• Two-component, solvent-based epoxy primer and undercoat
• Official Hempel product code 45551
• Base 45559 and Curing Agent 95360
• Mix at a ratio of 2:1 by volume
• Helps prevent osmotic blistering in glass fibre and GRP
• Protects against general corrosion
• Suitable for glass fibre, steel, aluminium and plywood
• For interior and exterior marine applications
• Suitable above and below the waterline
• Ideal for protecting keels and rudders
• Off-white standard shade, code 11630
• Semi-gloss finish
• Theoretical coverage of 8.2m² per litre
• Recommended dry film thickness of 60 microns
• Recommended wet film thickness of 122 microns
• Apply by brush, roller, paint pad or airless spray
• Use Hempel’s Thinner 845 (No. 5), product code 08451
• Six-hour brush pot life at 20°C
• Two-hour spray pot life at 20°C
• Touch dry in approximately three hours at 20°C
• Hard dry in approximately six hours at 20°C
• Fully cured in approximately seven days at 20°C
• Ready to sand in approximately 48 hours at 20°C
• Apply three to five coats to uncoated surfaces below the waterline
• Apply two coats to uncoated surfaces above the waterline
• Apply one full undiluted coat to previously coated surfaces
• Aluminium systems require at least 300 microns total dry film thickness
• Application and curing surface temperature must be above 10°C
• Relative humidity must remain below 85% during drying and curing

Frequently Asked Questions

What is Hempel’s Light Primer 45551 used for?
It is used as an epoxy primer and undercoat on glass fibre, steel, aluminium and plywood. It is suitable for marine surfaces above and below the waterline, including keels and rudders.

Does Hempel’s Light Primer help prevent osmosis?
Yes. Hempel states that Light Primer helps prevent osmotic blistering in glass fibre. The surface must be correctly prepared and the specified coating thickness and number of coats must be achieved.

Does it protect metal surfaces from corrosion?
Yes. Hempel’s Light Primer protects against general corrosion and is suitable for correctly prepared steel and aluminium.

Can it be applied to wood?
The current Hempel Product Data Sheet specifically lists plywood. It does not make a general compatibility claim for every type of solid wood. Dry, clean plywood should first be sealed with a suitable wood sealer, with Hempel’s Sealer 05991 listed as the recommended previous coat.

Can Hempel’s Light Primer be used above and below the waterline?
Yes. It is suitable for interior and exterior applications both above and below the waterline.

How many coats should be applied below the waterline?
Apply three to five coats to an uncoated surface below the waterline to obtain the required film thickness.

How many coats should be applied above the waterline?
Apply two coats to an uncoated surface above the waterline. Previously coated surfaces require one full undiluted coat, provided the existing coating is compatible and properly prepared.

What is the mixing ratio?
Mix two parts Hempel’s Light Primer Base 45559 with one part Curing Agent 95360 by volume. Mix thoroughly and allow the mixture to rest for several minutes before application.

Which thinner should be used?
Use Hempel’s Thinner 845 (No. 5), product code 08451. It is specified for both thinning the mixed product and cleaning application equipment.

How much area does one litre cover?
The theoretical spreading rate is 8.2m² per litre at the recommended 60-micron dry film thickness. Actual coverage will vary with the substrate, surface profile, application method and coating losses.

How can Hempel’s Light Primer be applied?
It can be applied by brush, roller, paint pad or airless spray. The mixed product may be thinned by up to 20% for brush, roller or paint-pad application and by up to 5% for airless spray.

What is the pot life after mixing?
At 20°C, the stated pot life is six hours for brush application and two hours for spray application.

What is the minimum application temperature?
The surface temperature must remain above 10°C during application and curing. Relative humidity must remain below 85% during drying and curing.

How long does Hempel’s Light Primer take to dry?
At 20°C, it is touch dry in approximately three hours, hard dry in six hours and fully cured in seven days. It is ready to sand after approximately 48 hours.

Can Hempel’s Light Primer be used before Hempel’s Brilliant Gloss?
Light Primer may form the epoxy foundation of an above-waterline system where specified. Hempel’s Primer Undercoat is the dedicated undercoat immediately before Hempel’s Brilliant Gloss. Follow the applicable Hempel paint system rather than treating Brilliant Gloss as a universally approved direct subsequent coat over Light Primer.