Aluminum alloys, such as AMG5 or AMG61They are highly corrosive, but even they need to be protected against aggressive environments. Water, especially salt water, and mechanical damage when mooring can destroy the natural oxide layer of metal in one season. A properly selected paint coating (LCP) is not only aesthetics, but also a guarantee of the durability of your boat.
The question of which paint is better to paint an aluminum boat worries many owners, since not all compounds have sufficient adhesion to this metal. Misconception of the material can lead to peeling of the coating and accelerated development of electrochemical corrosion. In this article, we will examine the chemical basis of the interaction of paint with aluminum and choose the optimal solution for your budget.
The modern market offers a variety of solutions, from budget alkydes to expensive epoxy systems. It's important to understandThe price often reflects not only the brand, but also the chemical resistance and elasticity of the material. We will look at the key specifications of the different types of enamel so that you can make an informed choice.
Features of painting aluminum alloys
Aluminum is an amphotelic metal, which means it reacts with both acids and alkalis, and it instantly forms a thin film of aluminum oxide on its surface, which protects the deep layers from oxidation. adhesion If you just put the normal enamel on the cleaned aluminum, it's likely to fall off at the first serious load.
There is also a risk of galvanic vapor if the paint contains components that are incompatible with aluminum, for example, the use of copper-based paints is strictly prohibited, as this will cause rapid corrosion of the body. For aluminum, only paints with neutral pH or containing zinc pigments that work as a protector are suitable.
Why does aluminum rust under paint?
Aluminum doesn't rust like iron, but it's pitting (point) corrosion-prone. If the LCP is damaged and the water gets to the metal, there's a local electroplating element at that point, and corrosion grows under the paint layer, blowing it up from the inside, which is why it's so important to properly prepare the surface and use insulating soils.
The quality of the staining needs to be taken into account in the operating environment: a boat that will walk on fresh water requires less aggressive protection than a boat for sea trips. In sea water, electrical conductivity is higher, and corrosion processes are much faster.
Overview of types of paints for aluminum
The paint selection is a fundamental step, and there are several major classes of paints on the market, each with its own advantages and disadvantages when working with paint. aluminum-alloy.
- 🛡️ Epoxy enamel: Two-component compounds that create a chemically resistant, durable coating, ideal for the bottom and waterline, but require precise mixing proportions.
- 🚀 Polyurethane paints: They are highly elastic and ultraviolet resistant, and are often used for superstructures and boards, as they retain color for a long time.
- ⚓ Zinc-containing enamel soils: They contain zinc dust, which provides electrochemical (protective) protection, and zinc sacrifices itself to protect aluminum.
- 💰 Alkyd enamel: Budget option: They dry quickly, but they have low mechanical strength and are short-lived in water, suitable for temporary repairs or interior spaces.
Two-part systems are particularly worth paying attention to, and they're more difficult to apply because they have limited lifespans after mixing, but the result is worth it. Interhead (Interlux) or Hempel (Hempel) Examples of brands offering professional lines for marine applications.
Surface Preparation: A Key Stage
Even the most expensive paint won't stick on a poorly prepared surface, it takes up to 70 percent of the time to work, and it determines 90 percent of the quality of the result, and it's critical for aluminum to remove all the oxides, old coatings and contaminants.
The first step is always to wash the case using special degreasing agents. Gasoline or white spirit can leave a greasy film, so it is better to use specialized degreasing agents. degreaser After degreasing, the surface must be completely dry.
☑️ Checklist for hull preparation
The machining is done by sandblasting or by an eccentric grinder, and it's important not to overdo it or create deep scratches that will become hotbeds of tension. If you use sandblasting, the abrasive must be clean and free of salts or iron to avoid putting them in soft aluminum.
⚠️ Warning: Never use steel brushes or abrasives that have been used to treat steel before. Iron particles embedded in aluminum will cause instant corrosion under the coating.
Printing technology
The ground is the link between the metal and the finishing surface. grass-grass They're phosphoric acids, and they bond chemically to the oxide film, creating a rough structure for better adhesion.
The soil should be applied in a thin layer, avoiding leakage. The exposure time should strictly follow the manufacturer's instructions. If you hold the soil, it will have to be grinded to ensure the adhesion of the next layer. Undrawn soil will lead to defects in the finishing paint.
The table below compares the popular types of primers for aluminum boats:
| Type of primer | Basis | Adhesion to Al | Time to dry |
|---|---|---|---|
| The Soil of the Earth (Wash Primer) | Polyvinylbutyral | Great. | 30-60 minutes. |
| epoxy | Epoxy resin | Good (requires grinding) | 4-12 hours |
| Zinc primer | Epoxide/Zincinc | High. | 2-6 hours |
| Acrylic soil | acrylic | Medium | 1-2 hours |
After drying the primer, the surface often requires light grinding (for example, an abrasive). P240 or P320Dust after grinding must be carefully removed with compressed air or a sticky napkin.
Painting the hull of the boat
Finishing paint can be done with a brush, roller or spray gun. For epoxy and polyurethane compounds, spray gun gives the best result, creating a smooth, glossy surface without stripes. However, working with a sprayer requires a respirator and good ventilation.
When painting with a brush or roller, it is important to follow the “wet edge” rule to avoid visible joints, apply the paint in 2-3 thin layers, the thick layer may not dry inside, remaining sticky, or flow under the influence of gravity on vertical surfaces.
Use paint tape to separate colors or protect windows. Remove the tape immediately after the paint has dried, without waiting for full polymerization, so as not to tear off a piece of fresh enamel along with the tape.
Temperature and humidity play an important role. +15°C before +25°CWhen high humidity on the surface of the epoxy can act "amine sweating" (fatty plaque), which will have to be washed off before the next layer.
⚠️ Warning: When working with two-component polyurethanes, be sure to use a high-quality respirator with carbon filters. The isocyanates contained in hardeners are toxic and can cause severe respiratory damage.
Anti-fouling coatings for the bottom
If the boat is intended for long-term storage on the water, without antifouling And not only does shells and algae spoil the view, but it also reduces speed and increases fuel consumption.
For aluminum, only copper-based antifouling with an insulating layer or special copper-free compounds are suitable. Copper in direct contact with aluminum creates a powerful galvanic pair where the aluminum will break down. So the layout of the layers looks like this: Aluminum -> Soiling soil -> Epoxy barrier soil -> Antifouling.
There are self-pollinating and solid antifouling, the former gradually dissolve in water, renewing the active layer, the latter work by the bicidal action of the surface, the choice depends on the speed of the boat and the salinity of the water.
The rule of antifouling is: Never apply copper-based paint directly to aluminum or zinc soil. Always need an insulating epoxy barrier.
Drying and commissioning
Full polymerization of paint can take anywhere from a few days to several weeks, depending on the type of composition and temperature. Although the paint can be dry "on a stick" after a few hours, chemical resistance is gained gradually.
The first descent into the water is better after the full drying cycle specified by the manufacturer. If you hurry, water can penetrate into the insufficiently hardened film, causing swelling. After descent, it is recommended to inspect the waterline for defects.
Care for new coatings is also important. Avoid using aggressive detergents with high pH. Regular washing with fresh water after each outing will extend the life of your LCP for years.
Can I paint a boat in the garage in winter?
Yes, you can, but only if you have a temperature regime (usually above 15°C) and good ventilation, in winter the air is drier, which is good for drying, but the cold metal will condense moisture from the air, the body must be warmer than the dew point.
How many layers of paint do you need to apply?
Optimal: 1 etching soil, 2 epoxy filler soil and 2-3 finish enamel layers, totaling 4-6 layers, which provides the necessary thickness of the film for waterproofing.
How do you dilute thickened paint?
Only the manufacturer's recommended solvent, usually xylene or special diluents of the same brand for epoxydoxy, and using acetone or 646 solvents can damage the chemical structure of the paint.
Do I need to grind every layer?
If the break between the layers exceeds the time specified in the instructions (usually 24 hours), grinding is required to create mechanical adhesion. If the painting is “wet” within the process window, grinding is not required.