How To Wet Sand A Fiberglass Boat | Know The Inside Tips And Tricks

Using mere compound on your fiberglass boat may not result in the glass finish you have in mind. So, what is the way? Just back down a bit and wet sand your fiberglass boat.

But how to wet sand a fiberglass boat? That is why we are here to answer your question. We will state the process and answer your questions to make you a pro in the fiberglass boat repair.

When Do You Need To Sand The Gelcoat On Fiberglass Boat?

So, how do you know if your boat needs restoring the oxidized gel coat? When the following happens, be sure to start the process!

  • With the gel coat all oxidized, or if it fades away, that’s when you need the sanding. With a faded gel coat, you can see your detailed reflection in the boat. But if there is minimum oxidation and a well-polished shine remains, only compounding the gel coat is enough. There is no need for wet sanding the oxidation. 
  • Sanding is a must if there is complete oxidation and the shine has faded away long ago. Sometimes you may see that even after compounding, you have not achieved the desired polished result, then you need to sand too.
  • Finally, sanding will get you through if your boat gets scratches or scabs you cannot take off. You may even need to get into the process of wet sanding the fiberglass boat for paint.

Should You be Wet Sanding Gelcoat by Hand?

Well, you should be wet sanding the edges of the boat when there is no interface pad or thinned gel coat.

However, machine sanding with a 6inch, 8mm DA sander or wet sanding a boat with an orbital sander with an interface pad would give better results. If pigtails come in the way, remember to set the machine not higher than level two.

If you need to wet sand by hand, do remember to check out the proper process on how to wet sand a boat by hand. You don’t want to mess with your precious fiberglass boat, you know!

Note: Are You Looking For?

How To Wet Sand A Fiberglass Boat: Digging Into The Process

Now, for the one you’ve been eagerly waiting for. Let’s get into the process. You can carry out the following steps to wet sanding a boat with wet sandpaper or a sander as your preference. 

  • You can start with an 800 grit wet-dry sandpaper. The sandpapers that we prefer mostly are 3M, sunlight, and Mirka abralon. Although loading them takes a while, they last way longer than the rest. Yes, it is possible to wet-sand by hand if you use a rubber block, but if you want our recommendations, we think an electric DA orbital sander can accomplish the work with much ease. 
  • If you are wet sanding by hand, remember to soak the paper in fresh water and use it. Be careful while you sand the corners of the boat or the top of your hull since these are usually the places with the thinnest gel coat. 
  • Now, if you’re handling an electric sander like a pro, make sure to use a spray bottle to mist the boat surface. To prepare the water mixture, add a few drops of detergent to keep the boat wet for longer or for evenly misting the surface. Now, rinse through the whole surface and carefully the burn-through areas. After the rinsing session, use a dry cloth to dry out the surface; it will give you a low glare visual at the coat. Now, for the sanding, go for rotating movements. Keep wet-sanding till the hull’s surface has reached a consistent matt finish. When you are done with the sanding, rinse with water to remove the residue. 

So, now that we know how to do the basics of wet sanding; let’s get into the details with the equipment and process. 

  • After the cleaning, start with 800 grit sandpaper. You can use an excellent DA orbital sander; for instance, the Dewalt sander can be a good option. So, do a 3×3 or 2×2 section with your sander in hand. Sand the same surface 3-4 times for the desired result. Apply equal pressure throughout the surface for a consistent sanding result when sanding.
  • Next up, you need to sand the same area with higher grit sandpaper, say 1000, and then increase to 1500 in the same manner as we mentioned above. 
  • You can cease the job at 1500 grit or even go higher like 2000. Then wipe off the hull surface. 
  • You need a buffer to compound the scabs and scratches as you finish sanding. A suitable quality compound is what you need to get rid of the blemishes. The sanding only unveiled the primary scratched fiberglass surface by taking the Gelcoat. 
  • A 3M material finishing compound will work great for taking off the scabs. Go back to your 3×3 or 2×2 area and apply the compound; later on, compound the scratches using a brand new woolen pad. 
  • The next step is to wax up the surface using good-quality wax. We suggest the Collinite 925.
  • And that’s it! By following the steps thoroughly, you will have shiny fiberglass bought looking brand new.

Also, if you need to know how to wet sand a jet ski, it’s somewhat the same process. So, it’s like, one bullet getting two shots right here!

Frequently Asked Questions

How much does it cost to wet sand a boat?

  • For an average 21ft boat, professionals’ total cost for wet sanding a fiberglass boat can cost about $700-$750.

What is grit sandpaper suitable for a fiberglass boat?

  • For polishing or priming the fiberglass boat, you can start with 800 grit sandpaper or 400 grit sandpaper, respectively. For a better gel coat polish, you can increase the grit numbers to 1500, 2000, or 3000. If you end on lower grit, it will need more polishing than ending at higher grit.

What is a DA sander?

  • The complete form of DA is dual-action. The sander is such that its head orbits in an oval shape and rotates on its own as well. The combined action of the sander allows it to give off a buffing outcome and more polished sanding.

Final Words

You might be having a hard time when you need to wet sand your gel-coated fiberglass boat. But that’s only if you are not aware of the right tricks and techniques on how to wet sand a fiberglass bass boat. Now that we have thoroughly explained each step, it shouldn’t be a big deal.

Hence, if that shine is missing from your precious boat, and if you have a strict budget to work with, following these steps can save both your boat shine and your credit card bills. So, let’s get started right away!

Jack K. Pride
Jack K. Pride

Jack K. Pride is an accomplished author and a prominent figure in the boating community. With a passion for boats and a deep understanding of the maritime industry, he has been sharing his expertise through his compelling articles on

Known for his insightful and informative writing style, Jack's articles provide valuable insights, tips, and knowledge to boat enthusiasts worldwide. His dedication to the subject matter and commitment to delivering high-quality content makes him a trusted voice in the boating world.

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