Polishing and Restoring Aluminum Pontoons.
Should I polish my pontoons to a chrome finish or restore them to a mill finish?
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The advantage of a chrome finish on an aluminum or pontoon boat is appearance. Humans like shiny things. The disadvantage is that the process is dirty, expensive (multiple products are required), time consuming (10 to 15 hours per pontoon) and afterwards, maintenance goes up exponentially.
Most people don’t understand aluminum or how to work with it. It’s a great material for building boats, but it too has its limitations. I’ll try to explain a few basics: Most aluminum, especially that which use for boat manufacture, is an alloy of different metals and additives to give it its final properties of strength, corrosion resistance, malleability, weldability, etc. Aluminum is a very reactive metal and its natural color is silver or chrome. When exposed to oxygen, either from the atmosphere or from water, it forms coating of aluminum oxide to protect it from reacting and deteriorating further. This is what gives aluminum its milky or whitish appearance. The initial coating of oxide happens very quickly, within milliseconds, of it being scratched or abraded. It’s a process known as Passivation. Over time the coating increases in thickness and becomes increasingly white in color.
Mill Finish denotes the appearance of the metal when it is manufactured in the mill, before any other processing or treatment. Aluminum and aluminum alloys is smelted into blocks. The blocks are heated and then forced between a series of progressively tighter rollers to form sheets of the desired thickness. This rolling and stretching forms striation marks or a grain on the surface of the metal. The grain is typically “long” or parallel to the longest direction. When rolled and welded into pontoons, the grain is usually horizontal. Mills also offer a highly polished, reflective finish. This is achieved by grinding away the top, grainy, layer of the aluminum to reveal a smooth surface.
Most pontoons are manufactured using the mill finished aluminum as it’s less expensive to purchase and the finished product requires much less maintenance.
To achieve an aftermarket chrome finish, it’s necessary to grind away the top layer of aluminum to reveal the smooth surface beneath the grain. Sandpaper and various grades of rubbing compounds or metal polishes are used for this. Traditional rubbing compounds and metal polishes consist of an abrasive or grit of various size suspended in a wax or silicone and petrochemical solvent base. When used to polish aluminum, as soon as the grit scratches the surface to reveal the raw aluminum, it is instantaneously covered with the wax, silicone or oil, preventing contact with the oxygen in the atmosphere. And this is how the highly reflective chrome finish is achieved. The aluminum lacks natural passivation.
The problem is that the finish is only as stable and durable as the protective finish. As the wax, silicone and oil oxidizes or wears or is wiped away, the aluminum reacts with oxygen and begins its natural process of passivation. The wax or silicone deteriorates at different rates, depending on many factors such as radiation damage from the sun, abrasion from water during operation of the boat or soap and water from boat washing, attack by pollutants, the natural oxidation process, etc. and the resultant deterioration to the finish will also be irregular or spotty. To maintain the finish, you need to replenish the protective wax or silicone coating on a regular basis, otherwise you’ll have to go through the polishing process all over again.
If you use a clear coat, it needs to be solvent based and have the ability to penetrate through the wax or silicone. The problem here is that it is difficult for anything to attach to the aluminum and the best you can hope for is a temporary coating that will have to be replaced every year or two. Solvent based clear coats will not stand up to water immersion. Also, after a short while the coating will start to peel and needs to be stripped and replaced. That’s why, when painting aluminum, the painters first etch the aluminum to give it some tooth and apply chromate primers before painting. Even that process has its limitations, as witnessed by the pitting and delamination of paint on the lower leg of aluminum sterndrives, or outboards, which are kept in the water.
Aurora Marine has adopted different technologies that are aluminum as well as environment friendly in order to address the cleaning, brightening, restoration and protection of aluminum:
ALUMABUFF, aluminum buffing cream is water based and uses a combination of Hypexine, a proprietary leaching agent, and other cleaners, to assist in removing stain and tarnish, plus abating abrasives to clean and polish while minimizing the destructive cutting action of rubbing compounds. In other words, it is a highly effective surface cleaner with some abrasives to assist the cleaning process as opposed to cutting and grinding away the top layer of aluminum to reveal a clean surface underneath. Because it’s water based, the protective aluminum oxide layer is not removed. The idea is to clean and restore the aluminum to its original look and properties, without damage or destruction to the surface.
ALUMABUFF can clean and restore an average pontoon back to its original mill finish in less than 60 minutes compared to 10 to 15 hours required to grind and buff a pontoon to a chrome finish. Since it’s restored back to original, it will naturally withstand weathering, tarnish and staining much better and longer than a chrome finish, even without additional protection.
ALUMETRON is a clear, protective, polymeric coating that bonds chemically to the aluminum and is suitable for constant water immersion, even salt water. Because of the chemical bond with the aluminum, any abrasion damage will remain localized and will not induce delamination so it can be easily repaired in the field. ALUMETRON can last up to 10 years and is sold with a 5 Year warranty against cracking, peeling, yellowing and delamination.
ALUMETRON is water based and has an affinity for the protective aluminum oxide on the surface of the aluminum. It cannot bond properly to surfaces that are contaminated with oil, wax or silicone. If the contaminants are removed, the aluminum will passivate and trade some of its brilliant chrome finish for a slightly milky finish. The initial milky finish is normally imperceptible. Only then can ALUMETRON bond to the surface.
VS721 is a micro thin, clear, Foul Release coating and is suitable for underwater use as well as above the waterline. It is popular for application over ALUMETRON to reduce the attachment of marine fouling below the waterline as well as salt, dirt and pollutants above the waterline. It’s suitable for use in fresh as well as salt water. Since it provides a very slippery surface, it also reduces drag to improve the performance of the boat and reduce fuel consumption.
VS721 is an emulsion with an oil outer phase and is suitable for protecting chrome finished aluminum. It also contains UV inhibitors to protect against damage from the sun’s radiation. Although it offers greater protection than wax or silicone it still needs to be reapplied annually or even more frequently, depending on where and how the boat is used. If the boat is trailered and kept under cover, it will last much longer. If the boat is kept in the water, year round, it will require more frequent maintenance.