Gelcoat Revival!

By Andrew Spaulding, Crowley's Yacht Yard, andrew@crowleys.com

Gelcoat, which is a polyester resin, forms the outer-most layer of almost all production boats. Gelcoat forms a shiny outer surface and is purely cosmetic. The production boat building process starts when the gelcoat is sprayed into a highly polished female mold. Then layers of resin impregnated fiberglass are layered into the mold to form the hull. Some hulls are built by laying the fiberglass in dry and then infusing the resin, but either way the end result is an outer layer of gelcoat covering the structural hull.

Gelcoat is damaged by ultra-violet (UV) radiation from the sun. The gelcoat is oxidized by the UV and falls away exposing new gelcoat to the sunlight, thereby making the situation worse and worse as time passes. The best way to slow this process is to wax the boat once or twice per year from the moment it is new. Any wax that mentions UV protection will work. We prefer Four Seasons Trewax Boat Wax ($22.99 for 12 oz in the Crowley’s Ship Store) or Starbrite Premium Marine Polish with PTEF ($17.99/pt).

The smoother the gelcoat, the shinier the gelcoat will be. Straight out of the mold the gelcoat is very smooth and shiny. Once oxidation sets in and the gelcoat surface is damaged it becomes rougher, and rough is dull. There are a few different methods of reviving the original gelcoat shine. Which one you use depends on the extent of the oxidation.

For light oxidation, a good quality cleaner wax such as 3M Cleaner Wax ($15.99/pt in the Crowley’s Ship Store) will remove light oxidation and apply a coat of wax at the same time. For heavier damage a several step process using compound will be necessary. We recommend 3M Imperial Compound and Finishing ($44.99/qt) for this job. Before applying any wax or compound make sure you wash the boat thoroughly to remove dust, dirt and any other particulate debris that might scratch the surface.

Once the UV damage is so severe the hull looks like it was never waxed to begin with, you need to consider sanding the boat to renew the gelcoat. Since the damage to the surface of the gelcoat makes it rough robbing the gelcoat of its shine, wet sanding the hull with a very fine grit sand paper will remove the surface of the gelcoat. Go from wet sanding to a compound (more than one grit of compound may be needed depending on how deep the sanding scratches go into the gelcoat), then apply a polish to remove swirl marks and finally an application of wax and the boat should shine like new.

Of course, there are a few pitfalls with the wet sanding process. Potentially there are spots where the gelcoat is very thin, so it is possible to sand through the gelcoat while wet sanding. It is also possible to need several grits of compound to get all of the sanding scratches out. If you notice the gelcoat starting to go transparent, it is becoming very thin so stop the sanding.

I feel that the largest pitfall of wet sanding gelcoat is probably the least well understood. Due to the way the gelcoat cures originally, the surface gelcoat is the toughest. So when the underlying gelcoat that is exposed after wet sanding, it oxidizes faster than original. Since the wet sanding process can be fairly expensive compared to a simple wax job, a boat owner can be disappointed by the length of time the wet sand job lasts. To protect the gelcoat as much as possible, since gelcoat is rarely thick enough to wet sand twice, I recommend waxing once a month after a wet sand job.

One option to revive gelcoat that we didn’t discuss is painting over it with marine grade topcoat paint. Painting the boat is expensive (all inclusive $300/ft sale price August and September 2012), but it will look new for 10 years where wet sanding might only look great for a few years. As always, think about your plans for the boat over the next few years before committing to a big job.

Please let me know if you have any questions about gelcoat or any other boat maintenance issues.