Repairing Pitted Aluminum Boats: A Comprehensive Guide

Pitting is a type of corrosion that occurs on aluminium boats, causing small holes in the metal. This is often due to exposure to saltwater. To repair pitted aluminium boats, you must first clean the affected area. This can be done by rinsing with a power washer or hose, washing with a mild alkaline soap, and drying with a microfiber towel. Next, remove the corrosion using a method such as dry or wet sanding or with a razor blade. Once the area is smooth and free of pitting, polish and protect the surface with an aluminium polish and sealer. For deeper pits, an aluminium filler or putty can be used before polishing.

Identify the cause of pitting

Pitting is a type of corrosion that occurs on aluminium boats. It is caused by a process called depassivation, which involves the deterioration of protective coatings around the metal due to contact with a chloride. In the case of aluminium boats, the main culprit is saltwater.

However, there are other factors that can cause pitting. One of the most common is the use of treated lumber or plywood in the boat's construction, especially in areas that come into direct contact with aluminium, such as bunks or flooring. The chemicals used to treat wood can react with aluminium, leading to corrosion. This can be further exacerbated if the wood is exposed to moisture, as water can trap corrosive chemicals against the aluminium, accelerating the corrosion process.

Another potential cause of pitting is electrolysis, which can occur when electronics are improperly grounded to the hull, or when different metals come into contact with each other, leading to a galvanic reaction. This is often seen when aluminium boats are placed on top of galvanised steel trailers or equipment without proper isolation.

Additionally, certain types of fasteners and screws used in boat construction can also contribute to pitting. If the wrong type of metal is used, it can react with the aluminium, leading to corrosion. This is often seen with rusted screws or fasteners, which can eat away at the surrounding aluminium.

Finally, batteries can also be a source of corrosion if they are not properly wired or maintained. Leaking battery acid can cause widespread corrosion and pitting, especially if it is not cleaned up promptly.

To identify the cause of pitting on your aluminium boat, it is important to inspect the boat thoroughly and consider any areas where different materials come into contact. Look for signs of moisture or water intrusion, as well as the use of incompatible metals or treated wood. Regular maintenance and prompt cleaning of any corrosive substances can help prevent pitting and corrosion from becoming more severe.

Clean the aluminium surface

To repair pitted aluminium boats, it is important to first clean the aluminium surface. Here is a step-by-step guide:

Step 1: Remove all dirt and grime

Use a power washer or a hose to rinse off all the dirt, grime and residue from the aluminium surface. This step is crucial to ensure that the subsequent cleaning and repair steps are effective.

Step 2: Wash the surface with mild soap

Use a mild soap or dish soap to wash the aluminium surface. Avoid using soaps with high alkaline levels as they may strip off any existing wax coating. Once you're finished washing, thoroughly dry the surface with a microfiber towel.

Step 3: Remove corrosion

There are several methods you can use to remove corrosion and pitting from the aluminium surface:

• Dry Sanding: Start with a higher grit (200-400) sandpaper and gradually move to a finer grit (600-800). Use the more abrasive sandpaper to remove deep pits, and then switch to the finer paper for a smoother finish. Repeat this process two to three times, using finer grit sandpaper each time.
• Wet Sanding: This method is preferred by some as it produces less dust and clogs the sandpaper less frequently. Use sandpaper specifically designed for wet sanding (dry sandpaper will disintegrate). Start with a grit of around 200-400, mix a bowl of water with a few drops of dishwashing liquid, wet the sandpaper, and sand off the pitting. Finish by using a fine grit of around 600-800, just like in the dry sanding method.
• Razor Blade: Use a straight razor blade to carefully scratch off the damaged and corroded areas. This method is suitable for removing hard-to-reach pitting.

Step 4: Buff the sanded area

Use a rotating buffer or fine steel wool to buff the sanded area until it appears smooth and free of all pitting. If there are still some problem spots, repeat Step 3. Finish by wiping off all debris with a clean microfiber towel.

Remove corrosion

Removing corrosion from an aluminium boat is a complex process, and there are a few different methods you can try. Firstly, it is important to clean the aluminium surface thoroughly. Use a power washer or a hose to rinse off all the dirt and grime from the boat. Next, wash the surface with a mild soap, ensuring that it does not have high alkaline levels, as this may strip the wax from the surface. Once you have finished washing, dry the surface thoroughly with a microfiber towel.

Now, you are ready to remove the corrosion. There are a few different methods you can try:

Method 1: Dry Sanding

Begin with a higher grit (200-400) sandpaper and work your way to a finer grit (600-800). Use the more abrasive sandpaper to remove the deep pits, and then switch to the finer paper. Do two or three rounds of sanding, using a finer grit than the last for each round.

Method 2: Wet Sanding

Some people prefer to use a wet sanding method, as it does not produce as much dust and does not clog the sandpaper as often as dry sanding. For this method, use sandpaper specifically for wet sanding (dry sandpaper will fall apart). Start with a grit of around 200-400, mix a bowl of water with a few drops of dishwashing liquid, wet the paper, and sand the pitting off the aluminium. Finish using a fine grit of around 600-800, just like the dry sanding method.

Method 3: Razor Blade

Some boat owners prefer to use a razor blade to scratch off hard-to-remove pitting from aluminium. Take a straight razor blade and lightly scratch off the damaged areas.

Once you have removed the corrosion, use a rotating buffer or fine steel wool to buff the sanded area. Rub the surface until it appears smooth and free of all pitting. If you still have problem spots, repeat the sanding step. Finish by wiping off all debris with a clean microfiber towel.

Preventing Future Corrosion

Once you have smoothed out the aluminium surface, you can apply an aluminium polish and sealer using a clean cloth. This will not only brighten the metal but also defend it from further oxidation and pitting. Keep your boat clean and dry, and consider using a cover when it is not in use to prevent the build-up of dirt and grime, which can contribute to corrosion.

Buff the sanded area

Buffing the sanded area is an important step in repairing pitted aluminum on a boat. This process will smooth out the surface and remove any remaining corrosion or imperfections. Here are some detailed instructions to guide you through the buffing process:

Before you begin buffing, ensure that you have thoroughly dried the surface of the aluminum with a microfiber towel. This step is crucial to prevent any water spots or residue from interfering with the buffing process.

The tools you can use for buffing include a rotating buffer or fine steel wool. Start by attaching the fine steel wool to the rotating buffer if you choose to use one. If you are working on a smaller area or prefer more control, you can also use fine steel wool pads by hand. Begin buffing the sanded area with gentle, circular motions. Apply light to moderate pressure, and work the buffer across the surface until it appears smooth and uniform.

It is important to maintain an even speed and pressure while buffing to avoid creating scratches or gouges on the aluminum. Take your time and work in sections to ensure that you cover the entire sanded area effectively. If you encounter any problem spots or deeper pits that require additional attention, you can go over them again with finer-grit sandpaper before resuming the buffing process.

Once you have completed the buffing process, it is essential to wipe down the area with a clean microfiber towel to remove any debris or residue. This step will prepare the surface for the next stage of the repair process, which typically involves polishing and protecting the aluminum to prevent future corrosion.

By following these detailed instructions, you will effectively buff the sanded area on your aluminum boat, creating a smooth and uniform surface that is ready for further treatment. Remember to take your time, work in sections, and maintain a consistent speed and pressure for the best results.

Polish and protect

Once you have smoothed out the aluminium surface, it is time to polish and protect the metal. Apply an aluminium polish and sealer using a clean cloth. This will not only brighten the surface but also defend the aluminium from further oxidation and pitting.

For example, BoatLIFE's aluminium cleaner is a very effective polish and protectant. You can also use a rotating buffer or fine steel wool to buff the sanded area. Rub the surface until it appears smooth and free of all pitting. If you still have problem spots, repeat the previous step. Finish by wiping off all debris with a clean microfiber towel.

If you are looking for a more heavy-duty solution, you can use an aluminium filler or putty to fill in the depressions. This is recommended for deep pits that cannot be smoothed out with sanding alone.

Frequently asked questions