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Marine Paint Primers, Sealers and Undercoats FAQs

What Does Marine Primer Do?

Primers are the unsung heroes of the boat painting world. Some primers adhere to the underlying hull surface, enabling the topcoat to achieve a sound mechanical bond with the primer. In other cases, these unseen paint coatings separate the old topside paint from the new, preventing an adverse chemical reaction.

Other marine primers are designed as build-up coatings that seal and hide repairs. Higher solids primers can even fill small scratches. These primers can be sanded for a smooth, paintable surface.

How Do You Prime a Boat Before Painting?

Although the actual boat primer paint application is a straightforward process, thorough preparation is key to outstanding results. Performing an in-depth examination of the current paints condition is an essential first step.

If the existing coating is peeling, cracking, or shows large-scale separation, remove the entire coating down to the bare surface. Sanding, scraping, grinding, or paint stripping are good options for paint removal. Once you have a clean bare surface, proceed using the steps below.

  1. Clean a new boats bare fiberglass hull with a solvent wash/dewaxer. This combo should also remove any contamination on a previously painted hull.

  2. If you have good-condition existing paint, sand it with (wet or dry) 220-320 grit sandpaper. When the surface dries, wipe it with a cloth and solvent to remove dust residue.

  3. If you see localized damage, use a manufacturer-recommended epoxy filler or fairing compound to even out the rough spots.

How Do You Apply Marine Primer?

As with topside paint, you can use a roller, brush, or sprayer to apply primer to your boats hull. Add thinner as needed to create the right viscosity. This is especially important for spraying applications.

Do I Need to Prime Gelcoat Before Painting?

Yes, you should prime your boats gelcoat before painting it. If the gelcoat is in generally good shape, and shows no major crazing or cracking, the process is relatively simple.

Remove all debris and contaminants from the gelcoats surface. Next, apply a coat of primer. Carefully sand the primer, and then remove the sanding residue. Finally, apply the topcoat.

If your boats gelcoat shows heavy areas of crazing or cracking, that calls for extra preparation. If you see signs of damage, repair those areas before proceeding with the previous steps.

Do You Need to Prime Bare Fiberglass Before Painting?

Lets say you just purchased a brand-new boat, and it arrived from the factory without bottom paint. Or, maybe you own a boat that has never seen antifouling bottom paint before. In either case, you should prime the bare fiberglass before applying the appropriate coating.

First, clean the hull thoroughly to remove accumulated dirt and debris. Next, wipe the hull with a solvent to get rid of wax remnants from the factory mold. Now, you are ready to apply a quality primer designed for use with a compatible bottom paint.

The best marine primer for bare fiberglass is a 2-part epoxy primer. This coating has been formulated as a hard, strong base for its associated epoxy and polyurethane paint system.

Hardworking epoxy primers are known for their outstanding adhesion and filling capabilities. Epoxy primers are compatible with fiberglass, steel, and aluminum substrates. These versatile primers can be used below or above the waterline.

What Is an Epoxy Primer?

An epoxy primer for boats is a versatile compound that provides outstanding filling and paint adhesion benefits. These two-part systems are often utilized for their maximum anti-corrosion properties and their ability to keep moisture out. Together, these attributes are important in the prevention of osmosis and blistering.

Marine epoxy primer can be used on all substrates, including fiberglass, steel, and aluminum. They are designed to be used above or below a boats waterline.

What is a Barrier Coat?

Designed for fiberglass boats, a barrier coat is a special-purpose protective epoxy undercoat. When properly applied, it creates a moisture-resistant surface that greatly decreases the chances of gelcoat blisters. A barrier coat can also be a key component of a vessels hull repair system. If your boat experienced gelcoat blisters as a result of water permeation into the hull, you must resolve the blisters before doing anything else.

Once you have done that, applying a barrier coat will help to ensure that the blisters do not return and potentially cause serious damage to your boat. After you have finished the barrier coat application, you can roll on the antifouling paint.

What Is the Difference Between 1-Part and 2-Part Primers?

A 1-part primer has been formulated for use with 1-part paint systems. Examples include yacht enamels and one-part polyurethane paints. Do-it-yourselfers find it easy to work with 1-part paint systems. Use these versatile primers on above-the-waterline surfaces on fiberglass, wood, aluminum, and steel boats.

A 2-part epoxy primer provides a super-hard base that easily accommodates epoxy and polyurethane paints and components. These painting systems are trickier to use compared to 1-part paint systems. When applied correctly, however, a 2-part paint system yields a deep, rich gloss and a long-lasting finish.

Although the majority of topside primers are intended only for above-the-waterline use, a few primers are also approved for below-the-waterline application. Carefully review the product can, or view the manufacturers website, to confirm the usage instructions.

Where Do You Use an Epoxy Primer?

Epoxy primers are designed for use below and above the waterline. Regardless of the location, these versatile compounds are known for their excellent filling and adhesion properties. Although frequently used on fiberglass vessels, epoxy primers work equally well on substrates such as aluminum and steel. Epoxy primers include TotalBoat 2-part Epoxy Primer and Awlgrip 545 Epoxy Primer.

Specifically, 2-part epoxy primers are designed to provide a durable base for epoxy and polyurethane paint systems. These 2-part paint systems provide a deeper gloss and more durable finish compared to 1-part paint systems. However, 2-part application techniques are more complex than those of 1-part paint products.

What Is Topside Primer?

A well-applied topside primer performs three important functions prior to the application of topside paint. Designed for above-the-waterline applications, the primer bonds to the underlying hull surface. This bonding enables a compatible topside finish coating to mechanically bond to the primer.

Topside primer also seals and hides previous hull repairs. A higher solids primer can even fill tiny scratches. Finally, the primer creates a wall between your old and new topside paint, thus prohibiting adverse chemical reactions.

Most topside primers are 1-part primers that are designed for use with a matching 1-part paint system. Examples include yacht enamels, Monourethane-alkyd paints, and 1-part Polyurethane paints.

1-part paint systems are typically used on above-the-waterline surfaces on fiberglass, wood, steel, and aluminum boats. Do-it-yourselfers will find 1-part paint systems easy to work with.

Topside primer cure times vary by product, and temperature and humidity also come into play. Always consult the manufacturers literature for specific instructions. Use only in a well-ventilated area, and avoid repeated or prolonged skin contact.

Some 2-part universal epoxy primers, such as Awlgrip 545 and TotalBoat 2-part epoxy primer, may be used on topsides or for below-the-waterline applications. Epoxy primers are known for their superior adhesion and filling properties. These versatile compounds can be used on fiberglass, aluminum, and steel vessels.

What Is a Metal Primer?

A metal primer allows a finishing paint to better adhere to a bare metal surface. At the same time, the primer fills in imperfections on the substrate materials surface layer. If the metal object will have considerable exposure to moisture, especially saltwater, using a primer is strongly advised.

What Are Wood Primers and Sealers?

Marine wood primers and sealers are similar in function to fiberglass primers. Specifically, they prepare the wood for the application of paint or varnish. Cure times vary with the product and environmental factors. Use these chemicals only in well-ventilated areas, and minimize skin contact.

Wood Primers

Generally speaking, a wooden boat primer is designed to penetrate and bond with the wood. Some primers will hide previous coatings, and will also mask the emerging wood grain. Properly applied wood primer enables the paint to properly cure, and improves the final paint coatings waterproofing abilities.

Wood Sealers

A correctly applied wood sealer gives the wood a uniform finish before the paint or varnish application. Wood sealers dry very quickly, and are easy to sand to a very smooth finish.