One of the many reasons fiberglass was so readily accepted by the boat-owning public was the expectation that gelcoat would put an end to the ritual of springtime hull maintenance.
Although gelcoat has its strengths – it doesn’t need the regular attention painted wooden hulls require – it’s not the cure-all many envisioned. Gelcoat eventually suffers from oxidation that results in a dull, hazy or chalky appearance, it can undergo crazing (micro-cracking) or be diminished by simple wear and tear (nicks, dings and scratches). Depending upon the gelcoat’s chemical formulation, as well as the color and the substrate over which it is applied, it may only look “great” for three or four years and “okay” for five or six years before appearing “tired” in just seven or eight years. Where dark-colored gelcoats are concerned, these time frames may be considerably shorter. Of course, the effects vary from boat to boat and geographic region to region, but it’s not unusual for a dark gel-coated hull – blue, green, red or black – to be ready for paint in just a few, alarmingly short years.
Fortunately there is a solution that involves painting (the industry often uses the terms “paint” and “coating” interchangeably) both new and used vessels with linear polyurethane, a product that is particularly durable and long lasting. A leading manufacturer of two-part, linear polyurethane (LPU) paint describes its product as “a two-component, polyester based, light fast, linear aliphatic polyurethane coating with long lasting gloss and color retention, and outstanding chemical resistance. Low maintenance, no waxing, buffing, compounding or polishing is required.”
In my experience as the manager of a boat yard that maintains a number of LPU painted vessels and applies LPU products, none of these statements are sales hype; this is an accurate description of most two-part polyurethane coatings. They are essentially durable, plastic-like coatings that, when properly applied, look great for many years while enhancing the value of nearly any boat.
The chemical makeup of LPU paint is what gives it its durability and luster. The two-part nature of LPU means that it is chemically catalyzed, as opposed to simply air drying by solvent evaporation. The polyester base means it’s made of many repeating molecular chains similar to many plastics. Its resistance to fading, or color fastness, is legendary and it shrugs off many chemicals, cleansers and solvents as well as hydrocarbons such as diesel fuel and gasoline. Some teak cleaners will, however, attack LPU paints if they are not diluted or washed off immediately. (If you are using a teak cleaner around any painted or gelcoated surface, it’s best to keep the surface continuously wet or under running water.)
Although all LPU coatings are durable, it is in the dark colors where they excel; they’re capable of a decade or more of service without a noticeable degradation in pigment density, although this may induce a phenomenon known as post curing, which will be discussed later. The reference to “linear aliphaticï¿½VbCrLf in the above description refers to its organic, open-chain molecules, which readily interlink, providing LPUs with their legendary toughness. Polyurethanes are simply flexible resins, which means that these coatings are capable of expanding, contracting and bending when applied over a flexible substrate like fiberglass. There are tougher, more abrasion-resistant coatings (gelcoat, for instance), however, they sacrifice resiliency for durability, making them brittle. LPU’s flexibility, however, doesn’t mean it’s ill-suited for rigid, metallic substrates. In fact, some LPU products were originally designed for coating the exterior of commercial and military aircraft. In the recreational and commercial marine industry, it’s used on everything from fiberglass hulls and decks to aluminum and steel of all sorts, including spars and entire vessels.
There are two locations where LPU coatings do not perform well -wooden vessels and areas that are continuously submerged or wet, e.g., below the waterline and bilges. Wooden vessels are well known for their propensity to swell, contract and move as a result of the wood’s varying moisture content. Although LPU paints are flexible, they are not flexible enough to absorb this degree of movement. Typically, the coatings used on wooden vessels need to support the changes in moisture content, as well as the natural movement that occurs while the vessel is under sail or in differing sea states. Few, if any, coatings are capable of contending with this degree of movement and thus the paint requires re-application, as mentioned previously, on an annual or bi-annual basis.
The one exception to this rule involves the application of LPU paints over cold-molded wooden hulls and decks. These are essentially composite structures, fiberglass or epoxy resin with a thin reinforcement skin on the outside and wood on the inside. In this case, LPUs work as well as they do on other stable substrates such as fiberglass, aluminum and steel.
LPU coatings also tend to perform poorly when used below the waterline or if they remain continuously wet. This often happens when a vessel’s waterline is either incorrectly marked or when it is loaded for cruising, which will sometimes place the boot stripe several inches below the floating waterline. Other avoidances include using a terminally soaked companionway carpet or floor mat in proximity to LPU coating used on deck; and LPU is certain to fail when used in a bilge. The mode of failure in these “wetï¿½VbCrLf scenarios is osmotic blistering and adhesion failure. Because LPU is made up of many open molecular chains, water molecules are able to pass between them during prolonged contact, which results in a build up of water pressure beneath the coating, which in turn leads to the formation of a blister and loss of adhesion.
The ties that bind
Nearly every commercial painter, whether he or she is painting houses, automobiles, aircraft or boats, will tell you that preparation is everything. Where LPU paints are concerned, this is especially true and it extends to more than the actual condition of the surfaces that are to be coated. The applicator of LPU coatings must be part artist, part technician and part chemist. He or she must be intimately familiar with the characteristics of the chosen coating. There are a number of different LPU products; some share similar characteristics while others are dramatically different. Awlgrip and Imron, for example, are among the most popular in the marine industry, between which there are considerable application, performance and repair differences.
The LPU applicator must also ensure that any related products used before or during the application are fully compatible with the final or topcoat that is to be applied. This refers to the fillers and fairing compounds that may be applied to correct minor or major imperfections in the surface as well as primers, catalysts and thinners/reducers. Ideally, all of the products that are to be used, from fairing compound to topcoat, should be supplied by a like manufacturer. If this recommendation is followed, it’s nearly impossible to encounter the bane of all paint applicators: incompatibility between any of the aforementioned components.
The bonds that are achieved between any coating and the surface to which it is applied typically fall into one or both of two categories: mechanical and chemical. The first coat of either paint or primer that is applied to a surface may achieve only one type of bond – mechanical. That is, the surface that is to be coated is sanded or profiled in such a way that it provides a degree of roughness, micro crags, valleys, teeth and facets that provide a profile with which the coating tenaciously interlinks.
Chemical bonds, on the other hand, are typically achieved between primers and topcoats, and between successive layers or coatings of topcoats. In a chemical bond, the two coatings bind or interlock on a chemical level where their molecular chains are allowed to intertwine. Chemical bonds can be especially strong and long lasting, provided they are applied properly. The primary limiting factor in achieving a chemical bond is time. Coatings that are designed to chemically bind almost always have a specific time window within which they must be applied in order to achieve the necessary chemical reaction. If the critical time window is missed, then the chemical bond will not be achieved, which could lead to wholesale coating release.
Before your chosen paint professional has agreed to transform your boat (you should be entering into this only with a written, agreed-upon price or quote, including a description of work to be carried out and any contingencies clearly spelled out) from tired, chalky and crazed to lustrous, brilliant and the color of your choice, he or she must begin the process by assessing what you already have. This is a vitally important step in ensuring the quality of the finished product. If the existing surface or surfaces to be painted are old but otherwise sound gelcoat, you’re in luck; this is a relatively low-risk, predictable substrate over which paint may be applied.
From the novice’s point of view, even old gelcoat often looks exceptionally smooth, if not faded or crazed, while an older painted surface typically shows some uniformly irregular texture. This should not be confused with the uniformly regular texture of fiberglass reinforcement visible as a result of post curing. If, however, the surface has already been painted (it may be paint over gelcoat, aluminum or steel), the paint professional must carry out a few tests in order to ensure the existing coating is mechanically sound or still stuck to the substrate beneath it, as well as being compatible with the new coating that is to be applied (see sidebar).
If either of these tests are omitted, or if the results are not heeded, then there is no guarantee that the coatings beneath the newly applied coating will not release or otherwise suffer failures in successive years, months or even days after the work is complete. In fact, adhesion issues or faulty substrate coatings are often damaged by ordinary prepping and masking procedures that are carried out during the paint preparation and application process.
For gelcoated surfaces, a thorough inspection for the presence of cracks, blisters and crazing must be carried out next. Imperfections such as these tend to be magnified by the application of high-gloss LPU coatings. Gelcoat cracks in particular must be properly dealt with. While it may look good initially, in some cases simply skimming these flaws with a thin filler material will only lead to their reappearance after the paint work is complete. Some gelcoat cracks are superficial and exceptionally shallow; these can often be “reefed outï¿½VbCrLf and filled with fairing compound, then sanded smooth. If, however, these cracks are deeper, they may be indicative of other issues within the fiberglass laminate, in which case they are simply a symptom of a more serious problem.
If the substrate is moving or flexing at a bulkhead or chain plate attachment, for instance, structural reinforcement or at least an assessment of the area may be required to prevent the problem from reoccurring. LPU paint is considerably more resilient and flexible than gelcoat and as such, it tends not to craze or crack if it is applied over crazed gelcoat or gelcoat that is prone to crazing again. In the case of seriously crazed or cracked gelcoat finishes, it may be necessary to remove the gelcoat in its entirety, either by sanding or by using a specialized gelcoat peeling tool, before applying a primer and LPU paint.
A step in the LPU paint process that is often overlooked involves the removal of hardware. This may be relatively inconsequential where a hull is being painted since hulls usually don’t have very much in the way of hardware. (Through hull fittings are usually not removed as part of the paint process and if they are, they are typically painted the same color as the hull or boot stripe, depending upon where they are located.)
Why should hardware be removed prior to painting? The reasons are twofold. One, for nearly all paints, LPUs and otherwise, it is preferable to apply as contiguous a coating as possible, one that has few seams, particularly around items that are likely to be loaded or stressed, such as deck hardware. Seams and locations where paint abuts hardware are where nearly all otherwise properly applied paint failures begin. Thus, applying the coating in one continuous sheet and then installing the hardware on top of it makes for a considerably more durable coating.
Two, most bedding compounds are no longer reliable after a decade or so and most boats that are being painted are more than a decade old. Thus, the hardware is often due for rebedding anyway. Make no mistake about it, removing the hardware (typically exceptionally large or complex hardware items such as anchor stem fittings and binnacles are not removed as part of the paint process unless they show signs of leakage) can be time consuming; it may add 50 percent to the cost of a paint job. It is, however, worth the expense, in my opinion. The paint will last longer and this, presumably, is one of the reasons you’ve chosen to paint your boat with LPU and not ordinary enamel paint. Why handicap that application from the start by taking a shortcut and masking off rather than removing hardware?
Dewaxing the surface
One of the final and most important pre-paint application steps in the coating process involves dewaxing. Waxes, oils, and particularly silicones (the latter have become very popular in everything from lubricants to cleansers) and other contaminants can play havoc with LPU paints. If paint is applied over a surface that is contaminated with any of these items, the result is an unsightly island, often called a “fish eyeï¿½VbCrLf because of its oval shape, that repels the coating. If a hull or deck is sanded before these contaminants have been removed, the heat and abrasion of the sanding process will often cause them to melt and be driven into the substrate, making their subsequent removal even more difficult.
Contaminant removal often involves a two-step process. First, the area to be painted, hull or deck, is wiped down with a solvent-soaked rag (the solvent should be specified by the paint manufacturer), then another clean, dry rag is wiped over the solvent-washed area. (Even the rags should be specially designed for paint preparation use. They must be free of detergent residue, surfactants and other additives.) This, not surprisingly, is known as the two rag system. In doing this, the first rag emulsifies the contaminants, while the second one carries them away.
The surface is then sprayed with water in what is referred to as the sheeting process. If the water sheets, that is, there are no islands or beads, then it’s safe to assume that most or all of these contaminants have been removed. If the surface fails the sheet test, then the suspect area must be scrubbed with a powdered abrasive cleanser (Comet works well) and an abrasive material such as a 3M Scotchbrite pad. The sheet test must be performed repeatedly until the surface is free of contaminants.
The actual application of the topcoat and clear coat, if that has been specified (clear coats give that extra degree of shine, depth and durability), is now in the hands of your paint professional. Simply put, either a painter has the right touch for applying sprayed coatings or doesn’t. Before you sign on the dotted line, it may be worth asking to see a few of the yard’s and the specific painter’s paint jobs, preferably examples that are two or more years old. Look closely at these examples for runs, sags, drips, insects, dust, sanding swirls, or marks and other debris as well as what is known as “orange peelï¿½VbCrLf (this is an undesirable mottled surface effect that looks like the skin of an orange). Also, look for examples of poor masking or overspray. As a yard manager, few things bother me more than the painter or prep folk’s reluctance to properly mask surfaces, including the insides of hatches, lockers or scuppers.
Color selection and
There’s a famous Hereshoff quote like, “You can paint a boat two colors, white or black, and if you paint it black you’re a fool.ï¿½VbCrLf Although this is an extreme view, it has its merits. When folks come to my boat yard to talk about painting their boats, they usually have already decided on the color. These days, it’s likely to be blue, black, green or red, or a variant – these are the “inï¿½VbCrLf colors and there’s no doubt they look great. I can’t remember the last time I painted a boat white unless it was part of a repair.
I do my best to talk these folks out of the darker colors for several reasons. The primary issue that must be faced when going from a light color to a dark color involves the aforementioned problem of post curing. The temperature achieved by a dark-colored surface on a July day here in Virginia may be 160ï¿½ F or more, while a white or light-colored surface may only reach 100ï¿½ or 110ï¿½ F. This elevated temperature isn’t harmful to the laminate, per se, but it will cause it to cure more than it ever cured when it was dressed in white. The resultant post curing causes the resin to shrink, which often makes the cross weave pattern of the subsurface fiberglass reinforcement material to become visible – very visible in some cases. Most people consider this effect to be less than appealing, particularly on a freshly painted surface.
Depending on the environment and weather conditions, it may take a few months or years for this effect to manifest itself. For hulls that were already a dark color, the post curing has already occurred and it’s safe to assume it will not continue. In these cases, the visible cross weave pattern can be filled and faired during the prep process. If the fairing is properly carried out, you can probably count on a uniform, dark-colored surface that is free of post cure. Boat builders who know in advance that their hulls will be gelcoated or painted with a dark color will often specify a material known as Coremat in the lamination process. This fluffy, blanket-like product is applied to the inside of the mold during the lay-up between the gelcoat and the fiberglass reinforcement. It absorbs the shrinkage and is effective in preventing print through. If your hull was built using this or a similar material, print through may not be an issue.
Dark colors have a few other detrimental side effects. Thousands of extreme heating and cooling cycles will take their toll on bedding, particularly port lights and other large structures, as the substrate, fiberglass or metal alloy expands and contracts. Stressing bedding in this fashion often shortens its life and leads to leaks. And the heating is frequently uneven; half the boat is shaded by its own hull, leading to wracking or the “banana effect.ï¿½VbCrLf
Another obvious side effect of a dark-colored hull is what it can do to cabin temperature. If you own or have ever owned a dark-colored automobile, you are well aware of this effect; it’s great in the winter but less than pleasant during the summer months. This effect means that not only the cabin and its occupants will be warmer, but so will the refrigerator, making it work that much harder or more frequently, which equates to increased amp-hour requirements.
LPU paint is an excellent and, in my opinion, preferable alternative to gelcoat, particularly for dark colors. When properly applied by an experienced professional, most boat owners are thrilled with the results.
Contributing editor Steve C. D’Antonio is the yard manager at Zimmerman Marine in Cardinal, Va.