MINOR GEL-COAT SERVICE  

Understanding the properties of gel coat and its applications  may better help you when there is a need for some repairs on your motor/sailing yacht.

What is Gel coat?
(Article from Signet, 2000 Issue)

The initial laminate in the layered construction of a production fiberglass boat is something we call gel coat. Sprayed into a highly polished mold, it gives the boat both color and gloss. The structural layers of fiberglass are applied to the "back" side of the gel coat. This is opposite of the way most other products are manufactured, where the last step in production is to spray on the finish—presumably the reason it’s called the finish. When it comes to production-built boats, gel coat is the starting point.

Gel coat differs from paint in other important ways. Paint bonds to the underlying surface mechanically—by gripping microscopic scratches put there by sanding or etching. The bond between gel coat and the underlying laminates is molecular. Resin saturating the first layer of glass material combines with the exposed surface of the gel coat to form a single mass—not unlike pouring warm gelatin over cold. This is called chemical cross-linking, and it occurs because the gel coat resin and the polyester resin used to saturate the layers of fiberglass fabric are the same basic product. Gel coat is essentially pigmented polyester resin. Gel coat does not "flow out" like paint. Good paints are self-leveling—like water. They dry to a smooth, glossy finish. Gel coat behaves more like plaster, taking on the texture of the application tool. It can be thinned and sprayed to get a reasonably smooth finish, but the wet-look gloss characteristic of new fiberglass boats is due entirely to the polished interior surface of the mold.

Gel coat is also about 10 times as thick as a paint finish. This is both a blessing and a curse, as we will see.

Chalking
Well-applied gel coat (like everything else, there are quality differences between manufacturers) can look good for a decade with minimal care. An annual coat of wax doubles the gloss life, but the elements eventually erode the relatively soft gel coat.

The loss of gloss is due to this roughening of the surface. There are two strategies for restoring the gloss. One involves filling the microscopic surface pits; the other requires removing the rough top surface. Regardless of the restorative measure, the first step is always a thorough washing. However, detergents do not necessarily lift oil and grease from the gel coat’s pores. Oily contaminants must be removed if you are to get dependable results from wax or polish. Wearing rubber gloves to protect your skin, wipe the gel coat with a rag and acetone. Turn the rag often and replace it when you run out of clean areas.

Wax
Keeping gel coat coated with wax—starting when the boat is new—is the best way to prolong its life. The purpose of wax is to protect, but it also has restorative properties when the gel coat is not too badly weathered. The wax fills microscopic pitting in the gel coat and provides a smooth, reflective surface. The gentlest of all restorative measures, waxing, should be the first thing you try when attempting to restore the luster to your hull.

Polish
Polish is an abrasive—like extremely fine sandpaper. When wax fails to restore the shine, polish is the next step. Rather than filling the pits, polish grinds them off, exposing a fresh, smooth surface. Polishing is a mechanical process—you rub the surface with a circular motion until it becomes glassy. An electric buffer is highly recommended for this. For polish to cut evenly, you must first remove all wax from the surface using a de-wax solvent or toluene. After polishing, apply a coat of wax to protect the surface and improve the gloss. (Some polish products include wax in their formulations.)

Eastside Boat Manager now has a Professional Polish , specially formulated for gel-coat surfaces. It has been field tested for 8 years, and has proven to be in the "top 5 high ranking gel-coat polishes. Take a look and read about this product at " THE WEB STORE"

Compound
The next weapon in the arsenal is rubbing compound. Compound contains more aggressive abrasives than polish. Select a rubbing compound formulated for fiberglass and use it exactly like polish, rubbing it with a circular motion until the surface turns glassy. Because of the thickness of the gel coat, compound shouldn’t cut all the way through if you are careful not to rub in one place too long. If the gel coat starts to look transparent, stop. After the surface has been compounded, polish it, then coat it with wax and buff it. Providing the gel coat has adequate thickness—the boat might have been compounded previously—this process will restore the shine to gel coat in almost any condition. 

With the basic understanding that you have just gained, you can now determine what kind of repair is needed.