Marine Paint Application Techniques

Marine grade paint products like Interlux Toplac, Interlux Brightside Polyurethane, Pettit EZPoxy and Epifanes Polyurethane z-spar varnishes are ideal over gel coat, wood, epoxy or natural surfaces for above the water line application. The different products have minor differences in application and preparation techniques for the ideal result, and we will discuss the differences in these techniques. The costs of painting overtop of gel coat versus using gel coat has been discussed in a separate blog post “To Gel Coat or Not to Gel Coat, that is the question,” but in general applying marine paint is easier than using 2-part paints or catalysed gel coats. For the easiest application at the lowest cost, polyurethane paints are durable, water resistant, UV stable paint for outdoor and marine environments.

To begin we have to mention the quality and stability of the surface that is being painted will directly impact the lifespan, smoothness and glossiness of the top coat finish. Painting on raw wood, or pressure treated wood will drastically affect the lifespan of the paint because the raw woods are more likely to shrink and expand due to humidity and temperature which will stretch or shrink the paint can cause cracking in shorter periods of time. Pressure treated plywoods have been chemically treated to resist materials penetrating or sticking to the surface, so paints will have limited adhesion to waxy or oily surfaces. Epoxy barrier coated surfaces are significantly more stable, and fiberglassed, aluminum or composite surfaces (campers, trailers, boats, etc.) are going to be the most stable surfaces and have the most durable long-lasting finishes.

The first step is sanding and fairing the surfaces to be smooth and stable for paint. This can mean stripping or sanding away old damaged gel coats, paints or varnishes and repairing fiberglass damage. This step can take some time, but the paint will not fill any imperfections. The paint is quite thin so it will duplicate textures (even wood grain) if the surface is not sanded smooth. The largest portion of time on refinishing and painting is spent on this step.

The preparation of the surfaces before applying the marine paints is similar in technique so that the paint has the best opportunity to adhere to a smooth decontaminated surface. For raw uncoated wood the sanding must be more aggressive (180-240 grit) and the surface has to be washed and solvent wiped to remove dust and waxy or oil contaminants. Previously gel coated surfaces have to be sanded in the same range as raw uncoated wood, and all cracks and crazing has to be removed so the surface is stable. Marine paints will not fill spider cracks in lower layer gel coats or fiberglass. Aluminum has to be sand blasted, sanded and solvent wiped to remove oxidization before paint can be applied. Polyester (general purpose) resin and epoxy resin have to be sanded and solvent wiped to remove wax before paint can be applied. All epoxies and general-purpose polyesters must be wax decontaminated.

The next step is going to be priming the surfaces before applying marine paints. The manufacturers of Pettit and Interlux marine paints do recommend priming the surface before applying new product, specially, when changing from one product (ie: gel coat or polyester or epoxy) to polyurethane or enamel. Pettit 6149 EZ Prime and Interlux Prekote Primer or Epoxy Primekote offer high build primers that are easily sanded to make the surface smooth before the first coat of paint is applied. Every coat of primer must be fully cured and sanded between coats. Aluminum hulls must be primed with Pettit Rustlok 6980 or interlux Primocon primer before top coats can be applied.

The first coat of paint can be thinner for brush or spray application, however, not any solvent can be added to the formulated paints. Every manufacturer provides their particular formulated spray and brush thinners and they do not recommend adding turpentine, varsol or paint thinner to the paints due to the chemical interactions leading to inconsistent results. Most of the paints, unless being spray or coating raw and resinous woods. The best brush application technique is rolling and tipping the paint, which consists of a low nap foam roller and a high-density foam brush. Pettit recommends rolling and tipping by:

1. Apply paint to the roller. You should have enough paint loaded into the roller that you do not have to stop and reload the roller before tipping, but you do not want the paint dripping off of the roller.
2. Apply the paint to the surface with the roller painting in an arm’s length area, making sure to get good coverage. • Be sure to paint in at least two directions – opposing diagonals or horizontally and then vertically to get complete coverage.

• Finish rolling paint onto the edge where your next pass with start. There should be some overlap here to continue paint flow.

3. Now, using your foam or bristle brush, lightly dip the edge of the brush into your paint supply
4. Remove any excess paint, the tip should be just wet enough to glide on top of the paint.
5. Run the tip of the brush end over your paint. You may see a faint brush mark as you are doing this.
6. Drag the brush end in the opposite direction you rolled the paint on to remove any roller marks or stipple.
7. Hold the brush on a slight angle as to glide over the top of the painted surface without removing significant amounts of paint. Do not use a lot of pressure. • Any brush marks created will quickly disappear as the paint self-levels.

8. Apply paint to the roller again following step 1.
9. You must start at the end while slightly overlapping your last wet edge to maintain paint flow.
10. Continue with steps 2-9 until the entire surface has been painted. • After completing the project using the roll and tip method you will be tempted to go back and retouch some areas. It is important that you DO NOT do so. Slight imperfections will be taken out by either self-leveling of the paint or they can be addressed by the second coat.

11. Allow adequate drying time.
12. Sand the first coat lightly with 200 grit sandpaper.
13. Remove excess sanding residue with a tack cloth, vacuum or air hose.
14. Repeat steps 1-10 for subsequent coats of finish.

Intelux recommends spraying polyurethane marine paint through an HVLP sprayer with a 1.5-1.8 mm nozzle tip size at 50-65 psi. Spray application also requires an Interlux 216 Special Thinner. Pettit recommends up to 15-20% thinning of their product with Pettit Spraying Thinner. Allow the paint to fully cure and scuff sand with 220 grit sand paper between coats.

The second coat of paint is also recommended by all Marine Paint manufacturers because it increases scratch resistance and increases the life span of the paint. The paint is applied in thin coats, so for a rich and consistent paint color you will require a minimum of 2 coats. The more coats that are applied at when new paint is applied the longer the lifespan of the paint.

The cost of marine paint is very low when comparing them to gel coats, where the coverage of the marine paint is higher than gel coat. The average cost of marine paint in the quart size (946ml) is between $65-90 dollars with the coverage approximately 125-146 square feet. Gel coat coverage is significantly less due to the thickness of application but can be more durable in fully submerged applications. Gel coat can be hand applied but is best spray applied. Spraying does have some more wasted material due to over spraying and material left in the sprayer.

Sources Cited:

https://pettitpaint.com/products/diy-topside-paint/single-part-polyurethane/ez-poxy/

https://www.interlux.com/en/us/boat-paint/topcoat-finish/brightside-polyurethane

https://www.interlux.com/en/us/boat-paint/topcoat-finish/toplac-plus-us