Paint and Varnish

When it comes to finishing your project, it is not as simple as it used to be, a good quality exterior house paint used to be the recommended option, however technology has moved on significantly and you now have many options depending on your desired finish, funds, skill level, and equipment available.

Two-pack products will give you a superior and stronger finish than most others, however they can also be the most difficult to apply and repair (often require spraying). Two-pack paints are a very hard-curing paint which means they can crack if there is movement rather than stretch like a softer paint. If you are confident with your application of the two-pack products you shouldn’t have a problem given all surfaces to be coated should be stabilized (epoxy/fiberglass over plywood). We predominantly spray professional grade two pack products in our workshop that aren’t available off the shelf, as we strive for an automotive grade finish, which is unfortunately out of reach for many amateur builders.

It is also worth keeping in mind that some linear polyurethane products can't be polished/buffed which can make life difficult if you do not have much experience with two-pack application and are prone to creating minor imperfections that could otherwise be polished/buffed out.

The most commonly used these days for marine applications by amateur builders, and an excellent middle ground, is a marine grade single pack polyurethane product that can be brushed/rolled and tipped for a great finish if done correctly.

Our recommendation for most applications would be a marine grade single pack polyurethane product, if available, applied using the roll and tip method.

When it comes to both paint and varnish, International paints can be used to produce top quality results.

If you have trouble finding a marine grade single pack polyurethane product, the next step would simply be a suitable marine grade paint/varnish. You should have no problem sourcing this easily at a local hardware or paint store. Bunnings even has some varnishes that we have used in the past to good effect, e.g. Bondall Monocel marine grade varnish, or Feast Watson Spar Marine varnish. Once again, varnish can be applied easily and produce first-rate results using the roll and tip method.

CLC have a couple of excellent articles on painting and varnishing. Otherwise you can find another good overview of the different methods/paints here.

Stain

If you are considering staining plywood you will need to ensure you use an epoxy friendly stain. Mohawk - Ultra® Penetrating Stain (previously Behlen Solar-Lux) is a good option if you can find it, however others may be available. It is worth noting that producing a good and consistent stain finish can be tricky.

CLC's Notes:

https://clcboats.com/blogs/boatbuilding-tips/painting-with-marine-polyurethanes

Painting a boat used to be so easy. All you needed was a can of exterior enamel from the hardware store, a clean brush, some masking tape, and a clear day. A quick-and-dirty 'workboat finish' is still an option worth examining if you are out of time and patience.

Today, boatbuilders have access to an arsenal of high-tech coatings that can make a boat gleam like a new car. Two-part marine polyurethanes, such as Interlux Perfection, have a deep, rich gloss and abrasion resistance that exceeds fiberglass gelcoat. One-part polyurethanes are almost as glossy and durable, but far less expensive and much easier to apply. Old fashioned marine enamels and even water-based marine paints are also available, but overall most boatbuilders feel that one-part polyurethanes, such as Interlux Brightsides or Pettit EZPoxy, offer the best finish for the effort required and for the money spent.

For chemists and/or those who'd like a very technical dive into the chemistry of polyurethane paint, here's a good article.

Prepare the surface - Unfortunately, paint doesn't always stick to the modern, high-tech epoxy that we apply to our kayaks. The problem lies with a waxy surface residue known as 'amine blush' that's created on some epoxies as a byproduct of the epoxy cure. If you don't deal with the amine blush, your laboriously applied coat of paint will never dry; instead, it'll turn into pigmented bubble gum that must be scraped off with a razor blade.

Remove the amine film and other contaminants - After your hull is sanded, wipe down the hull with denatured alcohol on a sterile rag. (Rags with fabric softener or residue from your car's dipstick are big trouble.) Avoid using acetone; it's alleged to have contaminants that leave paint-killing residues.

The Interlux folks recommend further isolating the epoxy from the paint with an epoxy barrier coat. We've never used such a coating. Ostensibly it bonds well to an epoxy surface and seals away all of the associated contaminants while providing a hard, paint-ready surface.

What About Ordinary Primers? - An ordinary coat of oil-based primer will enhance the appearance of your hull by filling low spots that you can neither see nor feel until it's accentuated by the intense gloss of the polyurethane paint. A ‘hi-build' primer, such as Interlux's Pre-Kote Primer will even conceal some of the epoxy runs and other warts that you didn't catch before running out of sandpaper. Caution: ‘hi-build' primers contain titanium dioxide or talcum powder, and once cured can absorb enough moisture to defeat subsequent layers of paint. To avoid moisture build-up, apply it only on dry days, and apply your finish coats as soon as the primer is cured and sanded. Sand the primer thoroughly with 220 grit paper. Sanding hi-build primer sends up huge billowing clouds of white dust, so it's best to do it outside on a windy day. Fortunately, primer sands fast and leaves a very smooth surface. Don't worry if you sand through the primer where there are high spots; this is normal.

Use A Foam Roller And Foam Brush - Marine polyurethane paints must be applied thinly and evenly or they will 'sag.' Foam rollers and brushes are perfect because they don't hold much paint and you can throw them out when you're done. Use the roller to spread the paint; you should apply the paint so thinly that the roller almost feels dry. Depending on how quickly the paint is tacking up, stop every 24 inches or so and 'tip' out the bubbles left by the roller with a foam brush. Use only the lightest pressure on the brush, and always maintain a 'wet edge': make brush strokes in one direction only, moving from dry surface to wet. Never go back with your brush to catch 'holidays' or sags; these paints tack up very quickly, and you will invariably make the ugly spot worse. Save the fix for the next coat.

How Many Coats Of Paint? Applying the paint so thinly will probably require three coats for coverage, depending on the color and your patience. Wetsand with 400 grit between coats for maximum smoothness and to avoid removing too much of the thin coat.

Painting with polyurethanes, and its complicated preparations, can consume a large percent of your total building time. We think, however, that mirror-smooth hull paint of a tasteful color, set against a varnished deck and trim, is as perfect a boat finish as one can get.