The outer surface of a fiberglass boat is normally a special resin called gelcoat. Gelcoat has little structural value — the underlying laminates of resin-saturated glass fabric provide that — but gelcoat protects the hull and gives it its color and shine.
When the gelcoat was originally sprayed into the hull mold, it — like all gels — took on the shape and texture of the mold surface. The ultra high gloss most new boats exhibit is due entirely to the highly polished, mirror-like surface of the mold used in the original construction of the boat.
Time and exposure eventually erode the relatively soft surface of gelcoat, leaving it dull and chalky. Fortunately, the gloss usually can be restored.
The first step in restoring the gloss to dull gelcoat is always a thorough cleaning. Add a cup of detergent to a gallon of water — warm water is better — and use a sponge to wash the surface with this solution. Be sure to protect your hands with rubber gloves.
If mildew is present, add a cup of household bleach to your cleaning solution. Difficult stains like fish blood and waterline scum may require the direct application of a concentrated cleaner formulated for fiberglass. Rinse the clean surface thoroughly and let it dry.
For dependable results from wax or polish, the gelcoat surface must be completely free of oil and grease. Detergents often fail to fully remove these contaminants from porous gelcoat. Wipe the entire surface with a rag soaked in MEK (preferred) or acetone, turning the rag often and replacing it when you run out of clean areas. Again, protect your skin with thick rubber gloves.
How To Wax A Boat
Keeping gelcoat coated with wax-starting when the boat is new — is the best way to prolong its life. Regularly waxed gelcoat can retain its gloss for 15 years or more. The real purpose of a coat of wax is to protect, but wax also has restorative properties if the gelcoat is not too badly weathered.
Application instructions vary among brands, but in general you apply the wax with a cloth or foam pad using a circular motion. Let the wax dry to a haze, then buff away the excess with a soft cloth, such as an old bath towel. The remaining wax fills microscopic pitting in the gelcoat and provides a new, smooth, reflective surface.
Polish is not a coating, but rather an abrasive — like extremely fine sandpaper. Polishing removes the pitted surface rather than coating it. Use a soft cloth to apply polish to a small area at a time, rubbing with a circular motion until the surface becomes glassy. After polishing, you should apply a coat of wax to protect the surface and improve the gloss. Some polish products include wax in their formulations.
Using Rubbing Compound
If the gelcoat is weathered so badly that polish fails to restore its shine, you will need the stronger abrasives rubbing compound contains. Wax on the surface can cause the compound to cut unevenly, so first remove all wax by "sweeping" the surface in one direction — not back and forth — with rags saturated with dewax solvent or toluene.
Select a rubbing compound formulated for fiberglass and use it exactly like polish, rubbing it with a circular motion until the surface turns glassy. The gelcoat on your boat is about 10 times as thick as the paint on your car, so compound shouldn't cut all the way through it as long as you are careful not to rub in one place too long. If the gelcoat starts to look transparent, stop.
After the surface has been compounded, polish it, then coat it with wax and buff it. Providing the gelcoat has an adequate thickness — your boat might have been compounded previously — this process will restore the shine to fiberglass in almost any condition.
Do You Need an Electric Buffer?
You can wax, polish, and compound by hand, but on anything but the smallest boat, your arm is going to get very tired. An electric buffer takes much of the work out of keeping a boat shining and is less expensive and less painful than elbow replacement.
Electric buffers operate at relatively slow speeds, so don't try to "make do" with a polishing bonnet fitted to a disk sander or a sanding pad chucked into a drill. You will either ruin the surface or ruin the tool. A buffer with an orbital motion will leave fewer swirl marks.
In recent years a number of products have come on the market that claim to restore the surface of the gelcoat. Restorer formulations renew the gloss in essentially the same way as wax — by providing a new smooth surface — but without the need for buffing. Results can be dramatic, but because restorers are a plastic (acrylic) coating — similar to urethane varnish — they can wear off, flake off, and occasionally discolor. Restorer kits typically include a prep wash and sometimes a polish in addition to the restorer. A specialized stripper for removing old sealer is also necessary.
There are variations in the recommended application, but in general it is the same as already described — clean, polish, and coat. The acrylic sealer is usually water-thin, so applying it to the hull is much easier than, say, paste wax. And it dries to hard film, so no buffing is needed. However you do have to apply several coats — five is typical — to get a good shine. If the product you have selected doesn't include an applicator, use a sponge or a soft cloth to wipe the sealer onto the gelcoat. Drying times are short, so subsequent coats can generally be applied almost immediately.
A multicoat application can restore the shine to weathered gelcoat for up to a year, but when it is time to renew it, you will need to remove the old sealer using the special stripper supplied in the kit (or available separately). Apply five fresh coats of sealer and your boat should shine for another year.