Most boat outdrives are aluminum, and though this metal is more resistant to corrosion, it might still be a good idea to lay on some protective finish. The only problem is that paint doesn't stick very well to aluminum, so the preparation work is crucial to successfully paint your boat's outdrive.
- Remove the outdrive's original coating. Your outdrive may still have its original coating, albeit faded and scratched. You have to completely take this off before anything else. Start with a strong degreaser, then follow up with paint stripper. These are easily available in any car paint store. Remember to protect the outdrive's seals and bearing when you apply the paint strippers. An alternative to using these chemicals is plastic bead blasting. This process literally ‘blasts' the paint off the surface. This service may be available in a local machine shop. When using this mechanical method of removing paint, you should cover the pitot tube, as this is a vulnerable component of the outdrive. The cheapest but hardest way of removing the original paint is to use aluminum oxide sand paper and sand off the coating by hand.
- Remove rust and other contaminants on the outdrive. This next step in the painting job is called etching. Etching chemicals are available in any car, aviation or marine vehicle supply stores. These chemicals are either acids or bases and are pretty strong. It is imperative that you handle them with care and follow the manufacturer's instructions strictly. Ask store personnel which etching product is specifically used for aluminum. Once you've completed the application of these chemicals as per instruction, you can give the outdrive a good rinsing.
- Apply a special coating of Alodine. As mentioned above, paint doesn't stick very well to aluminum surfaces, but there is a special coating known as Alodine that is specifically made for preparing aluminum for painting and also helps the metal resist corrosion. Alodine is available in most paint supply stores. Again, you should carefully follow the manufacturer's instructions on proper application. If Alodine doesn't stick to certain spots or areas, you may need to re-sand or re-etch that area. After application of this special aluminum coating, let the outdrive air dry.
- Apply the paint. The most important thing to remember about this step is to avoid using any paint that has copper. Copper paint on an aluminum outdrive will turn it into a battery and wreck it once it's left on the water for too long. It is recommended to put on at least three coats of primer and two layers of topcoat. Make sure to use primer and topcoat paints that are compatible with each other. Whether you're using an air brush or a conventional brush, always apply the paint evenly for every layer.
The key to painting your outdrive is good preparation work. If the sanding and etching stages are not done properly, the paint is not likely to adhere to the surface, and you'll probably have to start all over again.