Direct application of fresh paint coating on top of the existing layer is possible only under the condition of complete chemical compatibility of materials and the absence of defects in adhesion. If you ignore the state check LAKKNew enamel may swell or peel off a few weeks after drying. The owner of the car should understand that saving on preparatory work often leads to the need for a complete repainting of the element, which costs much more than the initial quality repair.
The technological process requires a thorough diagnosis of coating thickness and type of materials previously applied. Modern. acrylic base paints require specific conditions for polymerization, which can be disturbed by the presence of silicone polyroles or bitumen spots on the surface. Before the start of work, degreasing and checking for the presence of hidden corrosion foci under the existing layer are mandatory.
In most cases, professional painters recommend removing the top glossy layer to a matte state to ensure a reliable grip. Use of quality soil-insulators allows you to block the possible manifestations of old spots and level the absorbent capacity of the surface. Ignoring this stage leads to defects known as “craters” or “orange peels” that cannot be eliminated by polishing.
Criteria for assessing the condition of old paint coating
Before making a decision on applying a new layer of paint, a detailed inspection of the surface of the body is necessary. Visual inspection in bright light allows you to identify microcracks that can become centers of detachment. If there are deep chips to metal or bloating on the surface, painting without complete cleaning and localization It's strictly forbidden.
Particular attention should be paid to the chemical resistance of the old coating. To do this, in an inconspicuous place (for example, inside the door opening), a small amount of solvent is applied, used in the new paint. If the old lacquer begins to soften or stick, then the materials inconsistentIt requires the complete removal of the old layer or the application of special insulating soil.
⚠️ Warning: Trying to paint over the inflated paint without removing the rust will cause corrosion to spread rapidly under the new layer, destroying the metal element in one season.
The thickness of the coating also plays a critical role. Excessive build-up of layers without need can lead to cracking of the LCP due to the difference in the coefficients of temperature expansion. Thickness measurement paint-coating A special device helps to determine whether it is worth taking the risk and adding new microns, or it is better to remove the old material completely.
Technology of surface preparation for painting
Quality preparation takes up to 80% of the time of the entire painting process and is a guarantee of the durability of the result. The first stage is always a thorough washing of the body using active foam to remove bitumen stains and silicones. After drying, the surface is treated antisilicone Two passages with the use of slender napkins.
Mechanical processing consists in creating drawings to improve adhesion. For this purpose, an abrasive material with a gradation is used. P800-P1000 for wet grinding or P400-P500 for dry. It is important not to rub the coating to metal in unnecessary places, maintaining the integrity of the factory soil.
- 🛠️ Degreasing the surface with a specialized composition.
- 🛠️ Fasting of glossy areas with abrasive materials.
- 🛠️ Purging with compressed air all joints and crevices.
- 🛠️ Final dust removal with a sticky napkin.
After machining, it is necessary to re-remove the dust and degrease the surface. Any remaining dust will become the center of the defect after the paint has dried. Use of the sticky-cloth It is a mandatory final touch before entering the paint chamber or preparing for local painting.
☑️ Checklist for body preparation
Compatibility of paint materials and soils
The issue of material compatibility is fundamental in body repair. Different types of paints have different chemical bases, and mixing or layering them can lead to irreversible reactions. For example, the application of paint on nitrobase over acrylic can cause wrinkling of the coating due to the aggressiveness of solvents.
The soils serve as a link between the old coating and the new material. Adhesive soils They create a chemical bond with smooth surfaces, while the filling soils level out the micro-relief. The correct selection of soil allows you to paint on almost any stable base, including old enamel, if they do not peel off.
| Type of old coating | Recommended soil | Type of new paint | The risk of conflict |
|---|---|---|---|
| Acrylic enamel | Acrylic soil | Acrylic/Baza | Low. |
| alkyd enamel | Isolating soil | Acrylic/Baza | Medium. |
| Melamine varnish | Adhesive primer | Anybody. | High-pitched |
| nitroemal | Complete removal | Anybody. | critical |
Using universal soils makes the task easier, but does not guarantee 100% results on complex surfaces. If you are in doubt about the origin of the old coating, the safest way is to apply a test layer on a test plate or in a hidden area. Chemical reaction It may not occur immediately, but during drying or heating.
Table of drying times
The time of drying soil depends on the air temperature. At +20 ° C, the acrylic soil dries for 30 minutes, at +10 ° C, the time increases to 1 hour. Use IR drying to speed up the process, but monitor the surface temperature so as not to cause the solvent to boil.
Risks and Defects in the Disruption of Technology
Violation of the technology of preparation or the wrong choice of materials leads to the appearance of various defects. One of the most common is flaking (exfoliation) when a new layer of paint moves away from the old layers. This is due to the absence of mechanical risks or the presence of a fat film.
Another common problem is the appearance of old defects through a new layer. If there were hidden chips or uneven putty under the old paint, the new glossy layer will only highlight these irregularities. It's possible. swelling due to residual moisture or corrosion that has continued to develop under the sealed layer of new paint.
⚠️ Attention: The appearance of matte spots or a change in hue immediately after painting indicates improper drying or incompatibility of solvents in the layers.
Craters and fish-eye occur when silicone or oil hits the surface before painting. It is almost impossible to remove such defects locally, a complete re-furbishment of the element is required. Therefore, cleanliness in the room and cleanliness tool They're paramount.
Essential tools and supplies
For high-quality painting on top of the old layer, a specific set of tools will be required. The main tool is a spray gun with a properly selected duse (usually 1.3-1.5 mm for base and varnish). The compressor must provide stable pressure to avoid torch pulsation.
Consumables include not only paint and varnish, but also high-quality solvents, hardeners and filters for paint. Use of cheap solvent Unknown origin can lead to matteness of the varnish or a long drying time. Personal protective equipment is also needed: a respirator with carbon filters and a protective suit.
- 🎨 Krascopult with a duse of 1.3-1.5 mm.
- 🎨 Compressor with receiver and moisture separator.
- 🎨 A grinder and abrasive circles.
- 🎨 A set of degreasers and sticky wipes.
It is important to monitor the cleanliness of the airflow. The ingestion of oil or water from the compressor on the stained surface is fatal for the result. Regular inspection and maintenance water-separator a mandatory procedure before each use.
Expert advice: Always use a fresh solvent recommended by the paint manufacturer. An old or inappropriate solvent can roll the paint right in the spray gun tank.
Final treatment and drying of the coating
The drying process is a critical stage in the formation of the final coating. Violation of the temperature regime or the time of interlayer drying leads to defects. Polymerization The varnish does not occur instantly, but within a few days, so it is not recommended to operate the car immediately after painting.
If a two-component varnish with a hardener is used, it is important to observe the mixing proportions. Excess hardener will make the coating fragile, and the lack - soft and susceptible to scratches. Drying in the chamber at a temperature of 60 ° C accelerates the process and increases the hardness of the coating.
After complete polymerization (usually after 2-4 weeks), it is possible to perform polishing to remove fine shavels. This gives the coating a deep gloss and levelles the transitions. However, you can only polish completely. hardened varnish, otherwise you can wipe the coating to the base.
⚠️ Warning: Do not wash your vehicle using active chemicals and do not apply polishes in the first 3-4 weeks after painting. The coating should be fully durable.
Main conclusion: Painting on the old layer is possible, but requires perfect preparation and compatibility check materials. Savings on soils and degreasing are unacceptable.
Can I paint with acrylic paint over alkyd enamel?
Without applying insulating soil - it is impossible. Acrylic paints have more aggressive solvents that can lift alkyd enamel, causing wrinkling. It is necessary either to completely remove the old layer, or to apply a special separating soil.
Do I need to remove all the old varnish before painting?
Complete removal is required only in the presence of serious defects (corrosion, cracks, detachment). If the old coating is strong and holds well, just wrap it with abrasive P800-P1000 to create adhesion.
How long can I wash my car after painting?
The first wash is recommended to be carried out no earlier than 2-3 weeks after painting, when the lacquer coating is finally polymerized. Until then, it is best to avoid contact with water and chemistry.
Why did the new paint swell after drying?
Bloating (boiling) is most often caused by incompatibility of solvents, application of a too thick layer, high drying temperature or poor degreasing of the surface before work.