The hull of a small vessel made of aluminum-magnesium alloy requires a special approach to protection, since standard methods of processing ferrous metal here categorically do not work. aluminum It's an active metal that oxidizes instantly in air to form the thinnest but strongest oxide film, and it protects the alloy from corrosion through, but it's a dielectric and prevents most paints from adhesing.
That's why. aluminum-boat It has to have specific chemical properties that allow it to "get in" with an inert oxide surface. Errors in the primer selection stage or in violation of degreasing technology lead to the fact that after one or two seasons the paint begins to swell in bubbles, opening the access of aggressive river or sea water to the metal. epoxy It is considered the gold standard for water motors and how to properly prepare the surface.
Features of corrosion of aluminum alloys
Many owners mistakenly believe that aluminum does not rust like steel, a misconception that is dangerous to the longevity of a boat. corrosion Aluminum is not typical of red streams, it is subject to pitting (point) corrosion, where the protective layer or welds are damaged, microscopic ulcers form, which over time can lead to depressurization of the bottom.
Particular danger is posed by galvanicThis is the result of aluminum contact with other metals in the electrolyte (water). If you put a stainless steel or brass motor on the trawler without proper insulation, the aluminum will start to break down, acting as an anode. soil-insulating This creates a barrier to prevent this electrochemical process.
Mechanical damage is also important, and aluminium is soft, and hitting rocks or logs often strips the paint to metal. primerWater will quickly flow under the coating, causing it to detach over a large area.
Before buying soil, be sure to check compatibility with a specific alloy (AMG5, AMG61), as the magnesium content affects the chemical activity of the surface.
Types of primers: epoxy, acid and zinc
The corrosion-resistant materials market offers several solutions, but not all of them are suitable for constant contact with water. Acid soils Wash primers are often used in aviation and primary processing, and they contain phosphoric acid, which poisons the metal to create roughness, but for a boat that is constantly in the water, an acid layer is not enough, it requires a mandatory overlap with an insulating layer.
The most reliable solution for water-engines is epoxyThey create a chemically and mechanically strong bond with the aluminum oxide film. Once polymerized, the epoxide becomes inert, does not let moisture and oxygen through, acting as a perfect barrier. It is important to use two-component compounds, where the hardener triggers the reaction, making the coating non-melting.
- 🛡️ Epoxy primers: provide maximum adhesion and water resistance, ideal for the bottom.
- 🧪 Acid reagents: They are good as the first layer for complex surfaces, but require overlapping.
- ⚓ Zinc-filled soils: They provide tread protection (sacrifice themselves), but require careful matching of compatibility with the finishing paint.
There are also single-componentThey're easy to apply, but they're not as durable and chemically durable as epoxy, and they can be considered temporary solutions, or for superstructures that don't come into contact with water all the time.
Surface preparation technology (Degrees of cleaning)
The quality of surface preparation determines 80% of the success of painting. Just washing a boat with a Fae is not enough. For aluminum, it is critical to remove not only dirt, but also fat film and oxidation products. blasting Or mechanical grinding to a metallic sheen.
After machining, chemical degreasing is necessary. solventKalosha gasoline or acetone can leave traces, so professionals use specialized chemistry, for example, to make a difference. Solvent 2020 It's important to wipe the surface with pure rags, changing it often so that you don't smear the fat on the surface.
⚠️ Warning: Do not use chlorine-containing solvents to degrease aluminum! Chlorine may cause corrosion under the coating in the future.
Between mechanical cleaning and application of soil should not take more than 4-6 hours, otherwise fresh metal again forms an oxide film, reducing adhesion. If you do not have time to load the surface at this time, the procedure of grinding and degreasing will have to repeat.
☑️ Checklist for primer preparation
Comparative table of specifications of primers
When choosing a material, it is important to rely on specifications, not just on price. Below is a comparison of the main types of formulations available on the market.
| Type of soil | Adhesion to Al | Water resistance | Difficulty of application | Term of service |
|---|---|---|---|---|
| 2K epoxy | High. | Great. | Medium (mixer needed) | 10+ years |
| Acid 1K | Medium | Medium | Low. | 3-5 years |
| zinc | High. | High. | Tall (severe) | 8-10 years |
| Acrylic | Low. | Low. | Low. | 1-2 years |
As you can see from the table, epoxy Zinc soils are good, but they require perfect application because they are difficult to grind to finish, and acid and acrylic options are best left for temporary repairs or interior spaces.
Instructions for applying soil to the body
The application process requires compliance with temperature and humidity, the optimal temperature of the air and surface is from +15 ° C to +25 ° C. At lower temperatures. epoxy may not react with the hardener, remaining sticky, and at high - too quickly polymerize, not having time to spread.
Mixing components should be done strictly according to the weight or volume specified in the manufacturer's instructions. Use measuring cups or kitchen scales. After mixing, the composition should be allowed to stand for 10-15 minutes (exposure time) to pass the initial chemical reaction and release air bubbles.
You can apply the soil with a brush, roller or spray gun. spray-free Or a brush, because it allows you to drive the material into the micropores of the metal, and the first layer is made thin (called the fog layer) to allow penetration into the relief, and the second and third layers are applied more abundantly after the previous one is dry.
Interlayer drying time
The drying time per lip is usually 4-6 hours at +20°C. However, full polymerization (strengthset) takes 7 days. If you apply the second layer too late (after 24-48 hours), you may need to lightly grind the first layer to improve adhesion. Always read the technical map (TDS) of a particular product.
Finishing and protection of seams
Once the soil is dry, the surface becomes matte and rough. Before applying the finishing enamel (polyurethane or epoxy), it is often recommended to pass the soil with a fine abrasive (P240-P320) to improve traction. Pay special attention to welds - these are the most vulnerable places.
For seams and angular connections, special connections can be used primer sealerAluminum has a high coefficient of thermal expansion, and hard paint at the seams can crack when temperatures change or when shocks strike, and an elastic coating compensates for these strains.
- 🎨 Polyurethane enamel: They give a glossy, beautiful look, resistant to UV radiation.
- 🛡️ Anti-fouling paints: This is necessary if the boat will be in the water for a long time (protection from algae).
- 🔧 Repair kits: Have a small jar of soil and paint on hand for local restoration of chips.
⚠️ Warning: Do not apply finishing paint to wet or "frozen" soil. Condensation caught under the paint will lead to immediate (blistering) after descent into the water.
The most common mistake is saving on the ground: cheap paint on expensive quality ground holds better than expensive paint on a poor or missing primer.
Common Mistakes and How to Avoid Them
One of the common mistakes is to apply the soil to the dust metal, and after grinding, the aluminum dust settles everywhere, and if it's not removed with a sticky napkin or a jet of compressed air, it will remain between the metal and the ground, acting as a separation layer, and the paint will fall off in layers.
Another mistake is the misalignment of the mixing ratios: some craftsmen put hardeners in their eyes, hoping that "the oil porridge will not spoil." In the case of chemistry, this is fatal: an excess of hardener will make the coating brittle, and a deficiency will never let it dry. Use accurate dispensers.
They're often ignored. mixture After mixing the two components, you have 30 minutes to 2 hours (depending on the temperature) to work, and if you mix a bucket of soil and go out for lunch, in an hour, the mixture in the bucket will turn into stone and you have to throw it away.
Can an aluminum boat be painted with ordinary car paint?
Technically, you can, but only if you use adhesive non-ferrous metal soil (e.g., epoxy-based) conventional car soils are often designed for steel or plastic and may not provide long-lasting protection in aggressive aquatic environments. Automotive enamel without the right soil will quickly peel off.
Do I need to remove the old paint completely?
If the old coating is solid, not swelled, and has no trace of corrosion, you can keep it in the metal, just wrap the surface with abrasive P180-P240, degrease and apply a compatible soil, but if there is doubt about the integrity of the old layer, it is better to remove everything to pure aluminum.
How much dry soil does the aluminum boat have?
The drying time depends on the temperature and type of soil. Epoxy soils dry "on a stick" 4-6 hours at +20 ° C. Full polymerization takes up to 7 days. Acid soils dry faster - about 30-60 minutes. Always follow the instructions on the manufacturer's can.
How to degrease aluminum before painting?
It is best to use specialized degreasing agents (antisilicones), which quickly evaporate and do not leave films. Acetone or solvent 646 are acceptable, but may require more thorough cleaning.