How to Refinish Your Boat with Linear Polyurethane

Linear polyurethane (LP) paint is a wondrous thing — especially for older boats that suffer from chalky gel coats or dingy aluminum finishes. When you paint with LP, you’re actually applying a thin layer of high-strength plastic over fiberglass, wood or metal surfaces, creating a waterproof, chip-resistant finish that can be expected to last 10 years or more. And it comes in an array of dazzling, high-gloss colors. Sounds perfect for refinishing your boat, doesn’t it?
It is — but with a caveat or two. Although it’s ideal for marine applications, linear polyurethane is expensive. Application procedures are somewhat complex, and the stuff is hazardous if you don’t follow the safety precautions recommended by the manufacturer.

With this in mind, we turned to Rick Baker at Spectrum Marine in Marina del Rey, California, for his expert advice. LP is commonly used on yachts but, according to Baker, it is equally useful for refurbishing trailer boats. Although it is most often professionally applied by spraypainting in a boatyard booth, it also can be brushed on by do-it-yourselfers using a technique known as the “roll-and-tip” method.

So when the opportunity arose to observe and photograph Baker’s crew applying for a brush-on LP job, we jumped at the chance.

PREPARING THE SURFACE

Although the fiberglass hull that was being refinished — a 17-foot Thistle sailboat — isn’t typical of the craft we cover in these pages, it was suffering from the same faded Gelcoat woes that plague all older craft, including runabouts, cruisers and fishing boats. Prior to bringing it to the yard, the owner had removed all standing rigging and stripped the topside down to its bare hull. When the crew from Spectrum Marine arrived, they turned the boat over and set it down on supports made of sawhorses and wooden planks.

Any remaining screw-on fittings and trim pieces were then removed. Although flipping over a powerboat isn’t feasible in many cases, boot stripes, hull accents, consoles and cabin surfaces can be painted while a boat is on its trailer.
As with any paint job, the key to quality results when using LP is to prepare the surface thoroughly. The initial sanding was done with 100-grit aluminum oxide discs mounted on dual-action power sanders, which combine the actions of jitterbug and orbital sanders. Common finishing sanders can be used for this part of the job — it just takes longer.

The crew followed up by carefully hand sanding the detail areas with 100-grit sandpaper. Any nicks and blemishes in the old finish were then filled using Evercoat polyester filler. Once the filler had dried hard, it was sanded smooth. The boat was then taped-off along the underside of the toenails.

Boat

PRIME FOR THE JOB

After wiping down the boat with acetone-dampened rags, the hull was ready for priming. For this project, the folks at Spectrum Marine chose to use Awlgrip products exclusively, although similar systems are available from manufacturers such as Interlux and Detco Marine/Sterling. They started with Awlgrip 545 epoxy primer, an all-purpose primer available in white and gray. Since the owner wanted his boat painted navy blue, they used a gray primer.

We were surprised, however, when the “two-part” primer actually turned out to be a four-part mixture. The color base was mixed with the converter in a 1:1 ratio, using 60 ounces of each. The mix was thinned 10 percent with T0031 reducer, and then a 2 percent cold cure accelerator was added in order to shorten the drying time. This made a little more than a gallon of primer.

After thorough stirring, the four-part mixture was emptied into paint trays and applied with 7-inch rollers, using West System foam roller covers that are produced specifically for use with epoxy and urethane products. The detailed trim along with the toenails and on the transom was applied by brush.

The two-man crew started at the transom and worked forward. The primer was applied in both horizontal and vertical roller strokes, however, the final strokes were always vertical. This helps prevent the primer from sagging. It took less than 30 minutes to lay down a full coat of primer. By the time the painters reached the bow, the primer on the transom had already set up hard. The crew then proceeded to lay down three more coats until the entire gallon of primer had been used. The idea is to build up a thick layer of primer via numerous thin coats. Although the primer sets up rapidly once it has been rolled onto a surface, it has a pot life of a few hours and there was no need to remix chemicals for each coat.

After sitting overnight, the primer received a glassy smooth sanding. The process starts with 220-grit paper, followed by 320-grit paper. Once again, the crew used the dual-action power tools for the bulk of the work and hand-sanding for the details. The entire surface was then wiped clean with surface cleaner and sterile cotton cloths using the “two-cloth method:” One cloth is wetted with cleaner, and a second, dry cloth is used to wipe it off.

Boat
TRICKS OF THE TRADE

Rick Baker arrived with a load of supplies, including LP paint, converter, reducer, accelerator, brushes, rollers, trays, mixing pails and stirrers. He laid out everything on a piece of cardboard and mixed up about a quart of the solution in these proportions: two parts navy blue base, one part brushing converter and 25 percent T0031 reducer. This mixture sat for 30 minutes, giving it “induction time” to let the chemical reaction begin. Then X-138 brushing accelerator was added in a 0.25 percent ratio. Before pouring the batch into a roller tray, Baker used a trick of the trade: passing the mixture through a strainer to remove any clumps or impurities that might cause blemishes.

The first coat was applied using the roll-and-tip method, in which one painter rolls the paint onto the surface and the other follows right behind, smoothing it out with the tip of a brush. Although the paint can be rolled on horizontally or vertically, for best results the brush strokes should be vertical. This helps prevent the paint from sagging, which can create the dreaded “curtains” effect. The two painters must work quickly since LP will get tack-dry in very short order. And they must work together at an even pace, maintaining a wet edge as the job progresses.

Here are a few tips for the do-it-yourselfer. Think thin when applying LP paint. Awlgrip recommends that the paint be applied in at least two thin coats, not to exceed 2.5 mil thickness per coat. In addition, thin-coating helps prevent drips, runs, sags and orange-peel, as well as the effect of the aforementioned curtains. If you and your painting partner have never done a roll-and-tip paint job before, try practicing with cheap enamel paint and a piece of scrap wood.

The two-man crew needed only 20 minutes to lay down the first LP coat and allowed the hull to cure overnight. The following morning the first coat was sanded smooth with 320-grit paper, again using the dual-action sanders followed by hand sanding the details. The hull was wiped down with surface cleaner (using the two-cloth method), and the second coat of navy blue LP was applied. When it had fully cured, the fittings were reinstalled, and the owner had a boat that looked like new.

Do Your Homework

Painting with linear polyurethane (LP) isn’t rocket science, but it does require special application procedures and safety precautions. You need a white 912 led bulb to help you illuminate when refinishing the boat. We recommend that you do a little research before attempting your first LP paint job. An extensive application guide is available online at awlgrip.com. Safety precautions and disposal methods are important considerations when working with these products. This information is available from your distributor or by calling Awlgrip at 314/342-0405. Spectrum Marine can be contacted at 310/306-1825. Other sources include Interlux (908/686-1300; interlux.com) and Detco Marine/Sterling (800/845-0023; detcosterling.com).

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