What boat primer do I need? All about boat primers!

What is the best primer and what primer is right for my boat? There are lots of different primers and we understand that choosing the right one can be quite tricky. In this article, we explain all about the different types of primers. We also help you find the right boat primer with our selection guide!

What is primer?

Primer is the first (base) layer you apply before applying a paint system, such as an topcoat or antifouling, to a boat. The primer protects the substrate and, above all, creates good adhesion between the surface and the paint system. Primers are available as 1-component primer and as 2-component primer.

Why do I need a primer?

Steel, aluminum, wood and polyester substrates are quite vulnerable in a nautical environment. The application of a priming system protects the substrate against corrosion, wood rot, osmosis and moisture penetration. Additionally, a primer provides a good adhesive layer between the boat's construction material and a subsequent coat of paint, such as an undercoat or antifouling. In short, a primer should absolutely not be missing when you start refinishing your boat.

Benefits of applying primer:

  • Protects against corrosion, wood rot, osmosis and moisture penetration.
  • Ensures better adhesion between the substrate and the next coat of paint.
  • Ensures a lasting end result.
  • Fills small damages and scratches.

When should you apply primer and when not?

A primer is generally applied in several layers to almost any 'bare' surface. For steel, aluminum and wood, a minimum of five coats of primer is recommended above the waterline. For the underwater hull, it is recommended to apply a minimum of six coats of primer, followed by 2 or 3 coats of antifouling. On a new polyester gelcoat, the application of a primer above the waterline is in principle not necessary. However, for long-lasting protection of the underwater hull, it is recommended to apply primer and antifouling. In this case, six coats of primer and two or three coats of antifouling will provide excellent protection. In practice, sometimes only one or two coats of primer are applied to a bare gelcoat. This layer then only serves as an “adhesive layer” for the antifouling and does not provide any other lasting protection to the substrate.

Should you sand before applying primer?

Before applying a primer, any bare surface should be carefully sanded or sanded. This is because a primer needs enough “grip points” to stay in place on the building material, otherwise it will not adhere. The "attachment points" are created by means of "sanding" or good, careful and regular sanding. It is best to use an eccentric rotation sander (with the correct sanding grain), in several passes (sanding the same place several times and in different directions).

Correct sanding size:

  • Bare steel and aluminium | P24-P40 grit.
  • Wood | P180-P220 grit.
  • Bare gelcoat | P180 grit.
  • Existing primer system | P180 grit.

Do you need to sand the primer before applying the next coat?

No, this is not actually necessary, provided that the primer's drying and repainting times are respected. This information is given in the product data sheet. You can find all the technical documentation on the primers product page, under "documents". If the drying and repainting times have been exceeded, the primer must be sanded before applying the next coat of paint. Sand a primer with waterproof sandpaper (P180 grit).

What primer do I need?

We supply a wide and complete range of boat primers from top brands such as International, HempelDe IJssel and Epifanes. These brands supply high-quality primers that are also very easy to use. So you are guaranteed a perfect result. In this article, we classify our primers by application: primers for above the waterline and primers for below the waterline. Next, it is important to look at the substrate of your boat. This is because not every primer is suitable for every surface.

Below the waterline primers

  • International Primocon Primer
    This 1-component vinyl primer is only suitable for use below the waterline. International Primocon Primer is used to build up a paint system from a bare surface or for local repairs. In addition, this primer is also used as an adhesion and sealing layer between an old or unknown antifouling and a fresh, new layer of antifouling.

  • International Interprotect
    Interprotect is a 2-component epoxy primer used to protect building material, both above and below the waterline. With six layers of Interprotect, a very strong, water vapour-tight paint system is achieved.
Please note: a 2-component primer cannot be applied over a 1-component product or system.
  • International Gelshield 200
    Gelshield 200 is a 2-part epoxy primer that has been optimized using microplates for good, long-lasting protection of polyester gelcoat. This product is typically used as a primer for areas below the waterline. With six layers of Gelshield 200, we obtain a very solid system, impervious to water vapor and the gelcoat is very well protected against the formation of osmosis. For older boats we recommend carrying out a non-destructive moisture measurement before painting with Gelshield 200, as the product is not suitable for application over gelcoat with a damp fiberglass laminate behind.
Please note: a 2-component primer cannot be applied over a 1-component product or system.
  • International Propeller Primer
    Propeller Primer is a fast-drying 1-component water-based primer that is highly resistant to cavitation forces. The product is specially formulated for use below the waterline on propellers, saildrives, sterndrives and/or tailpieces. Propeller Primer is finished with a hard antifouling from International to prevent fouling. After careful pre-treatment of the 'bare' surface, this primer can be applied in 1-2 layers of paint with a brush or a paint roller. Propeller Primer should be applied to the surface as soon as possible after sanding (and at least within eight hours). View the Propeller Primer Data Sheet if you want to know how to properly pre-treat the building material you are working with.

  • Hempel Underwater Primer
    Are you going to apply Hempel antifouling? Then first use Hempel's 1-component epoxy primer. This quick-drying primer is easy to use and has excellent adhesion to polyester, wood and steel surfaces. Apply at least 3 coats of Underwater Primer before applying the antifouling of your choice to the underwater hull. Hempel Silic Seal allows you to easily switch from antifouling to the Fouling Release Systeem (Hempel Silic One). You can apply the 2-component epoxy primer over old antifouling, provided it is in good condition. Suitable for use on all surfaces (except wood).                   

  • Hempel Light Primer
    This 2-component epoxy primer prevents and restores osmosis on polyester boats. Additionally, Hempel Light Primer, protects against general corrosion. The primer is suitable for polyester, steel, aluminum and laminated wood boats. You can also use the primer for applications above the waterline.
Please note: a 2-component primer cannot be applied over a 1-component product or system.
  • IJmopox ZF Primer
    This two-part rust-inhibiting epoxy primer is suitable for application to aluminum and plastic surfaces, but is often used for metal surfaces. After treating the surface with IJmopox ZF Primer, the top coat can be applied with a two-component boat varnish, for example Double Coat DD Paint. ZF Primer can also be used above the waterline.  
Please note: a 2-component primer cannot be applied over a 1-component product or system.
  • Epifanes CR Antifouling Primer
    High quality one-component primer based on chlorinated rubber. Apply 5-6 coats of Epifanes CR Antifouling Primer for excellent anti-rust and preservation properties. The primer is suitable for steel, wood, aluminum and polyester surfaces.

Above the waterline primers

  • International One Up Primer
    One UP is a 1-component (2 in 1) primer and base coat that can be used for building a system from a bare substrate in 2 to 4 coats of paint (depending on building material ). International One Up also works as an intermediate coat over an existing paint system. The existing (old) paint system must, of course, have good adhesion to the substrate and the paint layers must not show defects. The existing paint system must be cleaned and degreased, then sanded with P220-P280 and dusted, before One UP can be applied.                            

    International One UP Primer is is for use above the waterline only and should be finished with an International 1-component topcoat. You easily apply the primer with a brush or paint roller. This one-component primer is easy to sand.  

Primer selection guide

In the diagram below you can read what primer you need for your application.

 Substrate Polyester Epoxy Steel Aluminum Wood
International Primocon Primer * * * * *
International One Up Primer * * *    
International Propeller Primer   * * *  
International Interprotect   * * * *
International Gelshield 200 * *      
IJmopox ZF Primer * * *   *
Variopox injection resin         *
Hempel Underwater Primer * * *   *
Hempel Silic Seal * * * *  
Hempel Light Primer * * * * *

Need advice on the right boat primer?

Do you need advice on the right primer for your boat? Do not hesitate to contact our specialists. We are happy to help you make your project successful!

E: support@polyestershoppen.com
T: +31 (0)85 022 00 90
WhatsApp: send us a text message

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