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Wet-Sanding Secrets You Should Know

Updated: Aug 12, 2023

In our experience detailing boats, we have earned the title "The Heavy Oxidation Removal Specialists." That's because 99.9% of the boats we detail are heavily oxidized. When we first got into the industry and spent time on the docks, I noticed most detail companies were focused on wash programs and waxing boats. In fact, I would notice marketing materials stating, "Sign-up for your seasonal wax before it's too late." However, I quickly noticed most boats require more than a seasonal wax, and some looked like they had been abandoned at the marina for several years. I wanted to avoid competing with the guys who just wanted to wash and wax boats, so I focused on the boats that needed the most care--the heavily oxidized boats. Thus, we began our quest to become known as the heavy oxidation removal specialists.

What is oxidation?

If this is just purchased your first boat, oxidation on a boat's gel coat surfaces refers to the chemical degradation and breakdown of the gel coat due to exposure to environmental elements, particularly UV radiation from the sun. Gelcoat is a durable layer applied to the fiberglass surfaces of a boat, providing a smooth and shiny finish while safeguarding the underlying material from water, dirt, and other external factors. However, over time, prolonged exposure to sunlight causes the gel coat's molecules to undergo oxidation, gradually losing it's original luster and color. This process creates a chalky, faded appearance on the gel coat, making the boat look aged and worn. Additionally, saltwater, pollution, and airborne contaminants can exacerbate the oxidation process, further contributing to the dulling of the gel coat's surface.

Before picture of a oxidized Malibu
Before picture of a oxidized Malibu

People often underestimate how difficult it is to remove oxidation from gel coat. I have interviewed several professionals over the years, some with over 30 years experience working with sanding abrasives and compounds in the boating industry and automotive industry, all say the same thing its about your processes and product and pad combinations. And even with a comprehensive knowledge of sanding techniques to manipulate gel coat surfaces to achieve a desired outcome, it's hard work at the end of the day! There isn't a magic compound on the market you can apply to the surface to get a desired result or at least we haven't found it yet.

After pic of oxidized Malibu

In a private detail group on Facebook with over 5,000 members from around the world Cobalt's and Rinkers come up. There's always the newbie that comes along and will claim, "they are all difficult!" But, that's because they haven't gotten their 10,000 hours in yet to notice a difference between gel coats and every boat is still a challenge to them. Therefore, it is important to vet the person who is willing to take on a oxidation removal project.

Before and After Heavy Oxidation Removal

Here's something you probably didn't know about wet sanding: In some instances it's better to dry sand than to wet sand. I know some of you are probably envisioning someone sanding on your boat with 80 grit sand paper. That does happen occasionally but only when you are prep sanding for a bottom paint. However, depending on how much abuse a hull has taken, a technician could dry sand with 400 grit to remove deep scratches in the gel coat. Then build it back up with higher grit sanding discs.

The Rules to Removing Sanding Marks

When removing sanding marks, the rule is to progressively refine the surface using finer and finer grits of sandpaper until the marks are completely eliminated and the surface achieves a smooth and uniform appearance.

Here are the general steps to follow when removing sanding marks:

  1. Start with coarser grit sandpaper: If you have noticeable sanding marks or scratches on the surface, begin with coarser grit sandpaper. The coarser grit will help level the surface and remove deeper marks effectively. As a general guideline, start with a grit between 600 and 800.

  2. Sand in a consistent direction: Always sand in the same direction to ensure even and uniform removal of sanding marks. Avoid circular or random motions, which may create new scratches or uneven spots.

  3. Gradually progress to finer grits: Switch to progressively finer grits after using the coarser grit. Move to medium grit, such as 1000 to 1500, followed by fine grit, like 2000 to 2500. This process will further smooth out the surface and reduce any remaining sanding marks.

  4. Check the surface regularly: During the sanding process, inspect the surface frequently under proper lighting conditions to identify any lingering marks. If you notice any, continue sanding with the next finer grit until the effects disappear.

  5. Use water or lubricant (wet sanding): Wet sanding can help prevent excessive material removal and reduce heat buildup, which may lead to additional damage. When using fine grits, wet the sandpaper or the surface with water or a suitable lubricant to aid the sanding process.

  6. Finish with cutting compound: Once all sanding marks have been removed and the surface is smooth use a cutting compound to restore the gel coat's shine and enhance the final finish.

Thus, to effectively wet sand/sand a boat to remove the oxidation, you must at least apply four levels of sanding. And you're not only going to just go over the surface a couple of times for the sake of sanding, but as you sand the surface, you are very intentional to receive the desired result. First, signs of oxidation should not be visible. Two, the previous sanding marks should be removed.

This blog post isn't meant to be an exhaustive wet sanding manifesto as with advances in technology, new products, differences in what conditions the boat has been exposed to, make and model, and color. There are many nuances that play a part in the outcomes of the final products.

In closing, below is an example of one of the challenges from a professional detailer that has the skill sets to address oxidation:

Heavy Oxidation

It's challenging when boat owners need help understanding the processes and are happy with subpar results. So most detailers have to customize/skip steps and still try to achieve a high-quality finish. One or two things happen when you skip steps:

  1. The oxidation will return almost immediately

  2. The oxidation will reappear by next season, and then we will repeat the process.

  3. The detailer is beating himself up for agreeing to do the job and this is where some will begin to cut even more corners in order to make a profit.

With scenario two, the oxidation return by the next season, and then we repeat the process. The problem with sanding and compounding on any boat every year is that there is only so much gel coat on that boat, and it will be a matter of time before you burn through. The goal when you wet-sand and do heavy compounding is that the next time the detailer does your boat, the detailer can put you in a lower package because now we are just maintaining the appearance rather than restoring. Scenario three happens often. Perhaps that is maybe the reason you are reading this article because you either been in the shoes of the boat detailer or on the receiving end as boat owner and wasn't pleased with the results.

Wet sanding/sanding is a complex subject. People think they will watch a YouTube video and become professional detailers. What professional detailers do is just like any other skilled trade. Contrary to popular opinion, it takes years of practice to master this trade. I wish you luck with your next project. And remember, prevention is always cheaper than cure.

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