Duraluminum watercraft, often referred to as "dural" waters, are among the most reliable in domestic waters. However, even the strongest D16T alloy is susceptible to corrosion, especially in joints and attachments, if the surface is not protected by a quality paint coating. Unlike steel, aluminum requires a specific approach to preparing and selecting materials, since standard soils may not provide proper adhesion or even accelerate oxidation.
Well-chosen dyeing for a dural boat is not just aesthetics, it's a critical barrier that extends the life of the hull for decades. Mistakes in the selection stage or the violation of degreasing technology often lead to the coating begins to swell and peel off after the first season of active operation. In this article, we will examine all the nuances of the process to make your boat look like new even after years of service.
It is important to understand that there are no universal solutions: the operating conditions in fresh water and in salty environments are radically different. What is great on the Volga may not withstand the aggressive effects of sea salt without additional protection, which is why you need to clearly determine where your vessel will be based and what loads it will experience before buying materials.
Features of corrosion of aluminum alloys
Aluminum and its alloys, such as duraluminium, have a unique property: when they come into contact with oxygen, they are instantly covered with a thin oxide film. This natural protection, called passivation, protects the metal from further destruction, but it is extremely thin and vulnerable to mechanical damage. If this film is broken by scratching or hitting a stone, the corrosion process can begin instantly, especially in contaminated water.
The most dangerous enemy of dural boats is electrochemical corrosion, which occurs when heterogeneous metals come into contact in the electrolyte (water). For example, if you install a steel bracket or brass propeller on the aluminum side without insulation, the base metal will begin to be destroyed intensively at the point of contact. galvanic pair It creates a current that literally “eats” aluminum, turning it into a loose mass.
⚠️ Attention: Never use copper or brass parts to attach directly to the hull of the dural boat without a special insulating gasket. Contact of these metals with aluminum in the water will lead to rapid through-rotting of the hull in the place of the fastener.
In addition, duraluminium is prone to pitting corrosion, which is the formation of deep but narrow ulcers, which occurs when aggressive chlorine ions or other chemical elements locally destroy the oxide layer. epoxy This is a necessary step, creating an impenetrable barrier between the aggressive environment and the metal.
How to distinguish active corrosion from plaque?
Active corrosion looks like loose whitish or gray growths that are easily washed with a finger, leaving a groove under it. Conventional lime plaque is hard and does not damage the structure of the metal underneath. If you see the shell after erasing the white plaque, it is corrosion that requires immediate treatment.
Selection of paint type for aluminum case
The paint market offers many options, but not all of them are suitable for dural boats. The main requirement for coating is high elasticity and excellent adhesion to non-ferrous metals. Conventional oil or alkyd paints, popular in everyday life, quickly lose their properties on water, crack on bends and can not withstand constant contact with moisture.
The most effective are two-component systems based on epoxy resins and polyurethanes. Epoxy compounds They create an incredibly strong, chemically resistant coating that acts as a great barrier to water, but they're afraid of UV light and can grind or turn yellow over time, so they're often used as soil or bottom layer.
For the upper decorative layer, the ideal choice is polyurethaneIt has a high gloss capacity, resistance to fading and mechanical shocks, modern polyurethane enamel allows you to obtain a coating that is not inferior to the automotive in quality and durability, and there are special zinc-containing soils that work on the principle of tread protection.
- 🎨 Epoxy soils: provide maximum adhesion and anticorrosion protection, but require overlapping with the finishing enamel.
- ⚓ Polyurethane enamel: give a resistant color, shine and resistance to abrasion, ideal for the board.
- 🛡️ Zinc primers: They create an active electrochemical protection, sacrificing themselves to preserve aluminum.
The best painting scheme for a dural boat is a combination of epoxy soil (2 layers) and polyurethane enamel (2-3 layers). Using only one type of material often does not provide a complete protection complex.
Technology of surface preparation for painting
The quality of the final coating depends 80% on how well the surface was prepared. Aluminum is a metal that requires careful degreasing, because any trace of oils, lubricants or silicone will detach the paint. The process begins with a complete washing of the case using specialized alkaline detergents.
After cleaning, you have to remove all the corrosion and the old, damaged coating, and you have to do it mechanically, you have to grind with abrasives or sandblast, and you don't have to overdo it, you don't have to remove too much metal, especially if the body is thin, and you have to get matte and rough, so you can get better adhesion.
The critical step is degreasing, and even if the metal looks pure, it can still have invisible films on it, and use non-ferrous metal degreasing agents or solvents like this. 646 or 647And the movement must be progressive, so that it doesn't smear the dirt, it picks it up.
☑️ Training checklist
After preparation, the surface should be painted for several hours to prevent re-oxidation. If you do not have time to apply the soil immediately, the clean metal can be preserved with a temporary composition, but it is better to plan the work so that the interval between grinding and priming is minimal.
Painting process
Applying paint to a dural boat requires compliance with temperature and humidity. The optimal temperature is from +15 to +25 degrees Celsius with humidity not exceeding 80%. Work in the open sun or in strong winds is not recommended, as this can lead to defects in drying and dust.
The substrate should be applied in thin layers, avoiding ducts. The first layer is often made more liquid (adding 5-10% solvent) so that it penetrates well into the metal micropores. After drying the first layer (time specified by the manufacturer on the jar), a second layer of normal viscosity is applied. Between the layers, light grinding may be required to remove the shavels.
Finish enamel is applied similarly, using a spray gun with a properly selected duse. For polyurethane enamels, a duse of 1.3-1.5 mm is usually used. It is important to observe interlayer exposure: if you hold the soil over, it will have to be grinded before applying the enamel to ensure adhesion.
| Parameter | Sound (Epoxy) | Enamel (Polyurethane) | Solvent |
|---|---|---|---|
| Viscosity | High. | Medium | Specialized |
| Drying time (20°C) | 4-6 hours | 12:24 hours. | - |
| Expenditure (g/m2) | 120-150 | 80-100 | - |
| Number of layers | 2 | 2-3 | - |
Use a dyeing powder (contrast spray) before applying the second layer of soil, which will show the places where the first layer lay too thin or was accidentally sanded.
Personal protective equipment and tools
Working with modern two-component formulations requires serious safety concerns. Solvent vapors and isocyanates in polyurethanes are toxic and can cause serious respiratory damage. A2P2 or higher is a prerequisite.
The best way to apply paint is to use a professional HVLP (High Volume Low Pressure) or LVLP (Low Volume Low Pressure) spray gun, which allows for high surface transport and minimizes fog. Cheap pneumatic sprayers can give you large shafts and overrun expensive enamel.
- 👓 Safety glasses: necessary to protect the eyes from the ingress of solvent and paint vapors.
- 🧤 Nitrile gloves: protect the skin of the hands from chemical effects and prevent the ingress of fat from the skin to the metal.
- 👕 Painting suit: disposable jumpsuit will protect clothes and skin from sticking paint and dust.
⚠️ Attention: When working with two-component polyurethanes, be sure to use a respirator with filters for organic vapors. Prolonged inhalation of isocyanate vapors can lead to irreversible changes in the lungs and asthma.
Typical mistakes and expert advice
One of the most common mistakes is painting without first testing the compatibility of materials. Some soils and enamels from different manufacturers may be chemically incompatible, leading to swelling or wrinkling of the coating. Always test staining on a small area or a separate plate.
Another common problem is the misalignment of the mixing ratios. Two-part systems require precision: if you add less hardener, the paint may not dry completely and remain sticky. If you add more, the coating will become too brittle and lose elasticity. Use dividing measuring tanks.
Experts also advise not to ignore the instructions on the temperature of storage of materials. If the can of paint was standing in the cold, it must be kept at room temperature for at least 24 hours before use. Cold paint has a different viscosity and may not mix correctly with the hardener.
Remember that minimum thickness To effectively protect duraluminum should be at least 80-100 microns. Attempting to save and apply one thin layer "for the species" will lead to the fact that in a year or two you will again encounter corrosion under the coating.
FAQ: Frequently asked questions
Can I paint a dural boat with ordinary car enamel?
Technically, you can do it with two-part acrylic or polyurethane car paint, but it has to be applied to a special ground for non-ferrous metals, and the usual one-part car enamels made of cans will not last long.
Should I remove the old paint if it is holding well?
The only place to remove the metal completely is where the old coating is corrosion and damage, and if the old coating is strong, it is enough to wrap it (mate) with abrasive P240-P320, degrease and paint over it, making sure that the materials are compatible.
How long after painting can I lower the boat into the water?
Full polymerization of most two-part systems takes 7 to 14 days. Although the surface may be dry to the touch after 24 hours, chemical resistance is gained longer. In the early days, it is better to avoid intensive operation.
How to remove paint if it is already dry?
Small stains can be gently sanded with abrasive P1500-P2000 with water, and then polished with polishing paste. Large floods will have to be cut with a blade, shpatted (if deep) or repainted whole board for uniformity.