From my collection of articles, this one by Randy Lowe:
Restoring oxidized gel-coat
Exposure to ozone and ultraviolet light causes polymers on the surface to gradually breakdown. Think of this oxidation process as plastic rust. As the surface oxidizes, pores open in the gel coat containing oxidized resin molecules called chalk. This chalk eventually turns the entire outer surface a dull, opaque color.
Another problem shared by both carnauba waxes and automotive sealant has to do with the very nature of gel coats. Gel coat is porous. When viewed under a microscope, a boat’s flat, smooth gel coat surface is millions of tiny holes. These holes, or pores, fill with microscopic grime; marine scum and salt crystals, which promote gel coat oxidation. Think of this oxidation as plastic rust. The contamination in the pores eats away the gel coat from the inside, filling the pores with a dull chalk-like color. As the chalk fills more pores, the entire gel coat surface will take on a dull, whitish finish.
Carnauba waxes and automotive sealant do not remove pre-existing micro-contamination in the pores. Worse, they seal the contamination in place where it continues to oxidize from the inside.
What can we do about this? Remove the surface layer with an abrasive. Sandpaper is generally too coarse, so a polish with a very fine abrasive or a coarse rubbing compound is used, followed by polishing and a wax or sealant. But it’s just about impossible to polish the surface to the high gloss of new gel-coat.
What products do we use?
Let’s break it down into the categories of:
• Compounds;
• Polishes;
• One step waxes/sealants;
• Waxes and sealants; and
• Restorers
Compounds: Use to restore a heavily oxidized finish
First thing to remember is the color of the compound. When working on chalky Gel-coat, the color will transfer. So it’s important to find compound that has little or no color (white). Dark brown or red color will soak in to the gel-coat permanently. Also, the coarser the compound, the more steps are necessary to restore gloss.
Some of the newer VOC compliant paint leveling glaze/compounds work great on gel coat with one down side: they are messy, and not something I would use in a mobile situation in a customers driveway.
Polishes: Use to restore a moderately oxidized finish
Select a polish with a fine grid compound that will remove moderate chalk and the scratches left by the compound. Color is still important here; this can be the first step if the finish is not heavily oxidized. My personal favorite here is a semi-liquid metal polish. The label on most metal polishes recommends use on fiberglass and plastic surfaces.
One-step waxes/sealants: Use to restore lightly oxidized finish
One-step can be used to maintain a gel coat finish in the first year of service and in the following years to keep the gloss at its best. To restoring a lightly oxidized finish, select one which has a super-fine compound, or non abrasive cleaner, with a synthetic wax/sealant. The metal polish can be used as well, for wholesale work or followed up with a wax/sealant for retail.
Waxes and sealants: Use on just polished gel coat
Gel coats should be protected with either a synthetic wax or a gel coat/fiberglass sealant. Both offer greater protection and extended durability because they seal the pores from air (ozone) better than a carnauba wax, as carnauba does not last on gel coat. If using a professional synthetic wax or gel coat/Fiberglas sealant, plan on applying a protective coating twice a year.
Select a product that has UV protection and no abrasives; the new automotive sealants work excellently on gel coat.
Restorers: Use when the finish is too far gone to polish
Sometimes the gel coat is too far gone and cannot be restored using the usual methods of buffing and polishing. This is where the restorers fit in, almost any liquid, including water, will provide a high gloss – for a while.
Fiberglass restorers use a water based emulsion of acrylic-urethane resin droplets, which form a clear, durable film when the restorer is applied, and the water evaporates. These emulsions have very low viscosities, much like water or liquid floor wax, and dry rapidly. This combination of characteristics makes multiple coats necessary; you don’t have to wait more than a few minutes before applying the next coat. Instructions usually call for five coats, with three maintenance coats at the end of each year.
Hope this helps a bit.
