Helena Frye
Wet sanding is a process used to restore the gel coat on a fiberglass boat. It involves using sandpaper and water to remove scratches, scuff marks, and dull areas, and to restore shine. The key to successful wet sanding is to take your time and use plenty of water to prevent over-sanding and breaking through the gel coat. After wet sanding, it is important to use a compound and wax to protect the gel coat and create a high-gloss finish.
Characteristics and Values Table for Wet Sanding a Fiberglass Boat
| Characteristics | Values |
|---|---|
| When to wet sand | When light oxidation occurs, you can skip sanding and just buff and wax. Wet sanding is for fairly bad oxidation. |
| Preparation | Remove all peripheral hardware from the boat, including cleats, handrails, lights, windshields, and decals. Wash the boat and remove any tar, bugs, etc. stuck on the glass. |
| Sanding process | Start with a lower grit sandpaper (400, 600, or 1200) and progress to a higher grit (800, 1500, 1000, 2000, or 3000). Use plenty of water and a few drops of dishwashing liquid or dish soap in the sanding water to make the paper slide easier. Rinse the surface after each grit. |
| Buffing | Use a high-speed buffer, not an orbital buffer. Use a wool bonnet or 3M waffle polishing pads (white for compounding/cutting and black for glazing/polishing). |
| Compound | Use a finishing compound like 3M Finesse It II or 3M Imperial Compound. |
| Glaze | Apply a high gloss glaze coat using 3M Final Glaze. |
| Wax | Use a hard Carnuba Marine Wax or Collinite. |
| Solvent | Use white vinegar to remove sanding dust particles and wash down the boat. |
| Avoiding damage | Be careful not to break through the existing gel coat, which is not very thick. Do not use acetone as it can deteriorate the gel coat. |
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What You'll Learn
Wet sanding tools and materials
Wet sanding is a meticulous process that can be time-consuming, especially for larger boats. It is a powerful technique to restore the shine and colour of a boat's gel coat finish. It is a cost-effective method to restore the appearance of a boat, compared to respraying gel. It is also a DIY-friendly process that allows boat owners to have direct control over the quality and detail of the work. However, it is important to be careful not to over-sand, as this can lead to thinning of the gel coat, potentially requiring professional repairs.
- Electric random orbital (RO) or dual-action orbital (DA) sander: A 6-inch random orbital polisher is recommended for efficiency. The Shurhold DA is a great entry-level device, and the Griots Garage G9 is the smoothest and best overall DA polisher for wet sanding.
- Interface pad: A 6-inch Mirka interface pad provides cushioning to prevent excess scratches.
- Sanding discs: Depending on your boat's condition, you may need various grits, such as 400, 500, 600, 800, 1000, 1200, 1500, and 2000. It is recommended to use 3M imperial paper, which does not load up easily and lasts a long time.
- Hose: A constant flow of water is essential for wet sanding.
- Guide coat: This is a contrasting chalk application that helps identify high and low spots on the gel coat.
- High-speed buffer: A high-speed buffer is necessary to cut through the faded clear coat. A cheap buffer is sufficient, and it does not need to be an expensive model.
- Waffle polishing pads: The 3M waffle polishing pads are recommended. Use the white pad for compounding/cutting and the black pad for glazing/polishing.
- Rubbing compound: 3M Perfect It Rubbing Compound #05973 and 3M Imperial Compound are recommended.
- Final glaze: 3M Final Glaze #06066 is suggested.
- Wax: Any hard Carnuba Marine Wax can be used. Collinite is recommended for the best results, but a high-quality automotive wax like Mothers Carnauba Cleaner wax will also work.
- Safety gear: Protective gear such as gloves and goggles is essential to protect yourself from potential hazards.
Additionally, you will need wet sandpaper or sanding materials such as aluminium oxide or silicon carbide. Aluminium oxide is a durable and versatile abrasive commonly used in boat sanding, especially for sanding and preparing fiberglass surfaces. Silicon carbide is ideal for aggressive sanding and faster material removal and is suitable for boat components made from fiberglass.
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Removing hardware and cleaning the boat
Before wet sanding a fiberglass boat, it is important to thoroughly clean the boat and remove any hardware that could obstruct the process.
Start by removing all peripheral hardware from the boat, including cleats, handrails, lights, windshields, decals, and anything else that can be unbolted from the top cap and consoles. This will make the wet sanding process easier and ensure that you can sand the entire surface evenly.
Next, wash the boat to remove any dirt, grime, or debris. Use a specialised boat cleaning soap and mix it with warm water according to the instructions. Wash the boat's gelcoat surface with a long-handled soft brush or sponge, and then rinse it off thoroughly with fresh water to remove any remaining soap, dirt, or debris. It is important to ensure that the gelcoat is free of oil and grease before moving on to the next step. You can use a non-scratching degreasing formula and a damp cloth to apply it to the surface, then wipe it off with a microfiber towel.
After washing and degreasing, dry the boat thoroughly with towels to prevent moisture buildup, which can lead to mildew growth. If there are any mildew stains present, apply a specialised mildew stain remover to get rid of them.
Once the boat is clean and dry, inspect the gelcoat for any stains, such as water stains, salt stains, or rust stains. Treat any stains with the appropriate products, such as salt removers or calcium, lime, and rust removers. Be careful not to use any harsh chemicals that could damage the delicate gelcoat surface.
Finally, if there are any barnacles present on the hull, use a plastic paint scraper or a wooden spatula to carefully remove them. This step requires special care to avoid damaging the gelcoat. Once the barnacles are removed, you may need to treat the remaining calcium rings, or "husk," with a calcium, lime, and rust remover, or sand them away with fine-grit wet and dry paper.
By following these steps, you will ensure that your fiberglass boat is properly cleaned and prepared for the wet sanding process.
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Wet sanding techniques
Wet sanding is a great way to restore the gel coat of a fiberglass boat. It is a labor-intensive process, but it can save you a lot of money compared to re-clearcoating. Here are some detailed instructions and techniques to help you get started:
Preparation:
Before you begin wet sanding, it is important to remove all peripheral hardware from the boat, including cleats, handrails, lights, windshields, decals, and anything else that can be unbolted from the top cap and consoles. This will make the job easier and provide fewer obstructions when using a buffer. Then, wash the boat and remove any tar, bugs, or other debris stuck on the glass.
Sanding Process:
- Start with the appropriate grit sandpaper: The grit you start with will depend on the condition of your boat and the extent of the repairs needed. For light oxidation, you may be able to skip sanding altogether and just buff and wax. For more severe oxidation, you may need to start with a lower grit, such as 300 or 400, and work your way up. A common progression is 600, 800, 1000, and 1200 grit. Remember to wet the sandpaper and use plenty of water during the sanding process. Dunk the paper frequently to clean the sanded material off. You can also add a few drops of dishwashing liquid to the sanding water to make the paper slide easier and prevent clogging.
- Sand the entire area: Use long, smooth strokes and apply even pressure. Keep feeling the sanded area as you work. If you feel any metal flakes or rough spots, stop sanding in that area to avoid sanding too deep and exposing the flakes.
- Rinse and repeat: After sanding with one grit, rinse the area with a hose or spray bottle, and then move on to the next finer grit. Continue this process until you have used the finest grit (usually 1200 or 2000).
- Wash the boat again: Once you have finished sanding, wash the boat again to remove any remaining glass particles. The surface should look dull but not faded.
Buffing and Polishing:
- Use a high-speed buffer: After sanding, it's time to buff the surface. Use a high-speed buffer with a white 3M waffle polishing pad and a rubbing compound. Work in small areas and move the buffer slowly to avoid burning the gel.
- Apply a glaze: Once you have finished compounding, wash off the compound and dry the boat. Then, use a black 3M pad on the high-speed buffer with a 3M final glaze to apply a high-gloss glaze coat.
- Finish with wax: After glazing, it's time to wax the surface. Collinite is a popular choice, but a high-quality automotive wax like Mothers Carnauba Cleaner wax will also work.
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Using a buffer
When using a buffer to wet sand a fibreglass boat, there are a few important things to keep in mind. Firstly, it is recommended to use a high-speed buffer, rather than an orbital buffer, as the high speed produces the heat needed to cut through the faded clearcoat. You can use a cheap buffer, as there is no need for an expensive model. In terms of sanding materials, you will need wet sandpaper in 1200, 1500, and 2000 grit. It is also recommended to use a 3M waffle polishing pad, with the white pad for compounding/cutting and the black pad for glazing/polishing.
Before using the buffer, it is important to remove all peripheral hardware from the boat, including cleats, handrails, lights, windshields, decals, and anything else that can be unbolted from the top cap and consoles. This will make the job easier and provide fewer obstructions when using the buffer. Once the hardware has been removed, wash the boat and remove any tar, bugs, or other debris stuck on the glass.
After wet sanding with plenty of water and a few drops of dishwashing liquid to make the paper slide easier, it is time to move on to the buffer. Dunk the paper often to clean the sanded material off and prevent it from clogging. When using the buffer, start with the white 3M pad and the rubbing compound. Work on small areas at a time and move the buffer slowly, avoiding keeping it in one spot for too long to prevent burning the gel.
Once you have finished compounding, wash off the compound and dry the boat. Then, switch to the black 3M pad and the 3M final glaze to put on a high-gloss glaze coat. Spin the buffer as fast as you can without building too much heat on the hull. Use a good thick wool bonnet on the buffer. After finishing, move on to a finishing compound, such as 3M Finesse-it II, and apply wax. It is recommended to use a high-quality wax like Collinite, but an automotive wax like Mothers Carnauba Cleaner wax can also work.
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Finishing and maintenance
Once you have wet sanded your fiberglass boat, you will need to finish the gel coat to protect it from deterioration. After wet sanding, you can use a finishing compound such as 3M Finesse-It II, which will help to remove any swirls. You should then apply wax to the gel coat. Collinite wax is recommended for the best results, but a high-quality automotive wax like Mothers Carnauba Cleaner wax will also work. You may need to apply several coats if using the latter.
After you have waxed the gel coat, you should wash it down with a mixture of white vinegar and water. This will remove any remaining sanding dust particles without stripping the wax. You can also use marine cleaners for this purpose. It is important to avoid using household soaps and detergents, as these will strip the wax.
To maintain your fiberglass boat, you should wax it regularly. If your boat is in the water for extended periods, it is recommended to wax the topside at least twice: once before it goes in the water and once halfway through the season. The hull should be waxed at least once before launching and again if the boat needs to be serviced.
If you are only dealing with light oxidation, you can skip the wet sanding process altogether and simply buff and wax the surface. However, for more severe oxidation, wet sanding is necessary to restore the gel coat.
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Frequently asked questions
You will need a high-speed buffer, not an orbital buffer, and wet sandpaper in 1200/1500/2000 grit. You will also need a 3M waffle polishing pad (white for compounding/cutting and black for glazing/polishing), 3M Perfect It Rubbing Compound #05973, 3M Final Glaze #06066, and hard Carnuba Marine Wax.
First, remove all peripheral hardware from the boat, including cleats, handrails, lights, windshields, and decals. Wash the boat and remove any tar or bugs. Next, wet sand with plenty of water and a few drops of dishwashing liquid, dunking the paper often to clean the sanded material off. Start with 1200-grit sandpaper, then rinse off with a hose and repeat with 1500-grit and 2000-grit sandpaper. After sanding, wash the boat again to get the glass clean of particles.
After wet sanding, use a high-speed buffer with a white 3M pad and a rubbing compound, moving the buffer slowly to avoid burning the gel. Once done, wash off the compound and dry the boat. Finally, use a black 3M pad on the high-speed buffer with a 3M final glaze to put on a high-gloss glaze coat.
