Gelcoat, the exterior finish on fiberglass boats, is a porous mix of polyester resins and pigments that must be sealed from the damaging effects of ultra-violet (UV) rays, salt, dirt and weather. Neglect it, and it becomes more porous, resins oxidize and what remains is a faded, dull finish.

There is no magic wipe-on, wipe-off remedy that removes oxidation and has a gloss that lasts a lifetime. Achieving a like-new shine isn’t very difficult, and doesn’t require a lot of extra work, especially if you invest in quality materials and tools.

Do these four steps to achieve a factory-new shine: wash to remove all contaminants; mechanically repair the gelcoat by sanding or compounding; chemically bond a protectant to the gelcoat to protect from further oxidation; and maintain the surface to extend longevity of protective coating.

Figure 1 Effect of sun’s rays on gelcoat: (top) Smooth, flat surface of new gelcoat reflects light just like a mirror; (bottom) UV breaks down the molecules, rain washes out the minute pieces that break away, creating a rough surface that reflects light at an angle and looks dull.

STEP 1
Scrub the surface thoroughly with a quality boat soap and water using a wash mitt or abrasive Scotch-Brite sponge. Flush with freshwater. Don’t use automotive soaps or household soaps, which may strip the wax or damage the gelcoat. If the application instructions recommend using a certain cleaner with a specific protectant (i.e. wax) to obtain the desired finish, follow the recommendations.

Use the “Oxidation Test” to determine condition of gelcoat. For surfaces in good condition that only require rewaxing, go to Step 3. For oxidized gelcoat, wipe with a solvent to remove silicone, wax or glaze buildup. Spray the surface with water, which should wet out rather than bead if all finishes are successfully removed.

Two options for repairing oxidized gelcoat are: fill the cavities with a quality wax or polish (hereafter referred to as “wax”); or knock down the high spots, either by compounding or sanding until the surface is flat, then follow with a filler. Just applying a wax on heavily oxidized gelcoat is a short-term repair. The surface has sheen when viewed from the side, but no deep luster, and rain in time washes away the wax. Oxidized gelcoat, whether light or medium, is best repaired by compounding or sanding to obtain a flat surface, filled with a glaze (or wax if a one-step product), then followed with a wax.

OXIDATION TEST (top): No Oxidation: Mirror image of ruler reflected in the gelcoat. (middle) Light Oxidation: Bottle reflected in the gelcoat appears cloudy, showing the label, but you cannot read the type. (bottom) Heavy oxidation: Little or no reflection of bottle in the gelcoat.

Different buffing pads are used when compounding and polishing. Wool pads are the most aggressive and the best for “cutting” gelcoat. Some detailers prefer foam pads, black for compounding, yellow for polishing. Use terrycloth pads (not shown) for applying and removing wax. When buffing a compound or glaze with a hand drill, operating it at 2,000 rpm to 3,000 rpm generates more heat and gives better cutting action.

Polisher/sander with 15cm (6") disk is run at 1,500 rpm. Keep the pad as flat as possible with pressure tilted on the trailing edge. A pad weighted on its leading edge tends to climb and take off and get caught in hardware. When working on sharp corners, feather the edges and always have the pad edge coming off the corner not into the corner so it doesn’t dig in. Continually move the pad so it doesn’t rotate in one place and “burn” the gelcoat. Put a hand on the surface. If it’s hot, it’s overworked.

Dressing Pads: Use a spur to clean pads before first time use to remove loose fibers. Cleaning used pads regularly to remove leftover sling doubles their life. Wear a mask when spurring a pad. Store used pads in Ziplock bags so they don’t become contaminated with other grits or dirt, dust and other contaminants. And don’t mix your grits. Use one pad for the compounding, one for glazing (if applying) and one for waxing.

BOAT WAX PRODUCTS

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