Painting car body parts: from preparation to final polishing

Painting body parts is one of the most popular procedures in auto repair, which can return the car to its original appearance or radically change its appearance. However, the quality of the result directly depends on compliance with the technology: incorrectly selected paint, poor surface preparation or improper drying conditions can lead to peeling, bubbles or uneven color. In this article, we'll walk you through the entire process—from materials selection to final polishing—with an emphasis on practical nuances, which are rarely mentioned in general instructions.

Regardless of whether you plan local repair (for example, touching up chips on a bumper) or complete repainting body element, the algorithm of actions remains similar. The main difference is the scale of work and equipment requirements. We will consider both options, paying attention budget decisions for garage conditions and professional technicians, which are used by painters in car repair shops. We will pay special attention compatibility of paints and varnishes with different types of plastic and metal - this is critical for the longevity of the result.

1. Selection of materials: paint, primer, varnish and consumables

The quality of paints and varnishes depends on 90% success. Cheap paints and primers can give a visually acceptable result, but after a year or two they will begin to crack or fade. When choosing, focus on base type (acrylic, alkyd, waterborne) and application system (single layer, base + varnish).

Suitable for most modern cars acrylic system (base + varnish), as it provides color depth and UV resistance. Alkyd enamels are cheaper, but less durable and require more thorough surface preparation. Water-based paints are more environmentally friendly, but are sensitive to humidity during application.

• 🔹 Paint: For metal parts - acrylic base (for example, Mobihel or Sikkens), for plastic - special flexible paints (for example, PPG Flex).
• 🔹 Ground: Epoxy for anti-corrosion protection, acrylic for alignment. For plastic - adhesive primer (for example, 3M Plastic & Paint Prep).
• 🔹 Varnish: HS (high hardness) for durability, MS (soft) for light polishing. Popular brands - Spies Hecker, Standox.
• 🔹 Consumables: Sandpaper (P80–P2000), degreaser (App W900), masking tape, anti-silicone.

⚠️ Attention: Never use nitro paints for plastic parts (bumpers, spoilers) - they will crack over time due to insufficient elasticity. Required for plastic primer with plasticizer.

2. Part preparation: the key to coating durability

Surface preparation takes up to 70% of the time of the entire process, but it depends on it whether the paint will last for years or will begin to peel off after a few months. Main stages:

1. Washing and degreasing. Use car shampoo and degreaser (for example, App W900). Pay special attention to joints and rusty areas.
2. Removing old coating. For metal - a grinder with an attachment P80–P120, for plastic - P180–P240 (so as not to overheat).
3. Straightening (if necessary). Dents are leveled out hammer and file, then checked wipe board.
4. Putty. Apply in 2-3 layers with drying between them. For plastic - elastic putty (for example, 3M Plastic Repair).

Critical remove all rust to metal. If pockets of corrosion remain, they will appear through a new coat of paint within 3-6 months. For processing use rust converter (for example, Tsinkar) or phosphoric acid.

⚠️ Attention: When sanding plastic parts (bumpers, moldings), do not use P80 and rougher - this will lead to microcracks, which will then appear under the paint.

3. Priming: why this is not an optional step

Many beginners skip priming or apply it “for show,” but this gross mistake. Soil performs three key functions:

1. Adhesion. Bonds paint to the surface (especially important for plastic and aluminum).
2. Anti-corrosion. Epoxy primers protect metal from rust.
3. Alignment. Acrylic primers mask minor scratches from sanding.

Application technology:

1. Apply primary soil (for example, epoxy) in 1 layer. Dry for 15–20 minutes.
2. Apply filling soil (acrylic) in 2–3 layers with interlayer drying for 5–10 minutes.
3. Sand the soil P400–P600 (wet method) to remove the “orange peel”.
4. Degrease before painting.

Soil type	Purpose	Drying time	Sanding
Epoxy	Anti-corrosion, adhesion	1–2 hours	Not required
Acrylic (filling)	Leveling the surface	30–60 minutes	P400–P600
Acidic (reactive)	Improved adhesion on “difficult” metals	10–15 minutes	Can't be sanded
For plastic	Plasticizer, prevents cracks	20–30 minutes	P500–P800

4. Painting: application techniques and typical mistakes

The most critical stage where errors lead to streaks, shagreen or uneven color. Basic rules:

• 🔹 Temperature. Optimal range - 20–25°C. At temperatures below 15°C the paint goes on “dry”, higher 30°C - may bubble.
• 🔹 Humidity. Not higher than 60%. At high humidity, paint forms "matte coating" ("powdered sugar" effect).
• 🔹 Distance to detail. Keep the spray gun at a distance 15–25 cm. Closer - drips, further - "dust".
• 🔹 Movement speed. Move the spray gun at speed 30–40 cm/sec, leading it parallel to the surface.

Application technology:

1. Base coat (for metallics). Apply in 2-3 layers with interlayer drying for 5-10 minutes. Each layer must be "wet", but without drips.
2. Varnish. It is applied in 2 layers: the first is a “fog” (easy, for adhesion), the second is a full “wet” layer. Drying between coats is 10 minutes.

Typical mistakes:

• 🚫 Incorrect paint thinning. Too thick - shagreen, too thin - drips. Follow the manufacturer's instructions for viscosity (measured viscometer).
• 🚫 Uneven application. If you hold the spray gun at an angle, one edge of the piece will be darker than the other.
• 🚫 Ignoring interlayer drying. If you apply varnish to a wet base, it will wrinkle and crack.

What to do if the paint bubbles?

If bubbles appear immediately after application, the cause may be too high a pressure in the spray gun (optimally 2–2.5 atm) or contaminated paint. It can only be corrected by sanding the defect and repainting. If bubbles appear after drying, moisture or incompatibility of layers is to blame (for example, alkyd paint over acrylic primer).

5. Drying and polishing: finishing touches

Even perfectly applied paint requires proper drying and polishing. Depends on it shine, scratch resistance and durability coverings.

Drying methods:

• 🔹 Natural. When 20°C — 24 hours until complete polymerization. Suitable for garage conditions.
• 🔹 Infrared. Lamps speed up the process up to 4–6 hours. It is important to keep the temperature no higher 60°C, otherwise the varnish will turn yellow.
• 🔹 Thermal chamber. Professional Method: 60°C within 1–2 hours. Gives maximum coating strength.

After drying is required polishing:

1. Wet sanding. Sandpaper P1500–P2000 Small defects (specks of dust, shagreen) are removed with water.
2. Polishing with paste. Use abrasive paste (for example, 3M Perfect-it) with a polishing machine. First hard circle (removes scratches), then soft (for shine).
3. Protective coating. Application ceramic composition or wax for protection against UV and chemicals.

6. Painting plastic parts: features and life hacks

Plastic elements (bumpers, moldings, mirrors) require special approach, since ordinary paint does not adhere to them due to low adhesion and high elasticity of the material. Key points:

• 🔹 Degreasing. Use antisilicone (for example, App W700), since plastic actively absorbs fats.
• 🔹 Primer for plastic. Required adhesive primer (for example, 3M Plastic & Paint Prep), which contains plasticizers.
• 🔹 Flexible paint. A regular acrylic base will crack if the bumper is deformed. Use elastic paints (for example, PPG Flex or Spies Hecker Permahyd).
• 🔹 Drying. Plastic takes longer to dry than metal - at least 48 hours at 20°C.

Life hack for bumpers: if the part has already been painted and the paint is peeling off, don’t sand it down to plastic - just matte it P500 and apply fresh adhesive primer. This will save time and materials.

⚠️ Attention: Never use acetone or solvent 646 for degreasing plastic - they corrode the surface and the paint will lie unevenly.

7. Typical problems after painting and how to avoid them

Even professionals sometimes have defects. Let's look at the most common ones and ways to prevent them:

Defect	Reason	How to avoid	How to fix
Drips	Paint too thick, spray gun too close	Thin the paint according to the instructions, keep the spray gun on 20–25 cm	Sanding P1200 + polishing
Shagreen	Low pressure in the spray gun, high viscosity	Keep pressure 2–2.5 atm, check the viscosity with a viscometer	Wet sanding P1500 + polishing
Matte coating	High humidity, polluted air	Painting in Humidity <60%, use filters on the spray gun	Polishing with abrasive paste
Peeling paint	Poor adhesion (wrong primer, greasy surface)	Thorough degreasing, use of adhesive primer	Complete paint stripping and repainting

If a defect is found immediately after painting (within 1-2 hours), it can be fixed without completely repainting. For example, drips are carefully removed varnish solvent (for example, App W100) and a swab, after which the area is tinted.

8. Advice from professionals: how to save money without losing quality

Painting at a car repair shop is expensive, but many jobs can be done yourself without sacrificing quality. Here are some tips from painters with 10 years of experience:

• 💰 Buy paint from authorized dealers. There are many fakes on the market Mobihel or DuPont, which are outwardly indistinguishable, but last 1-2 seasons.
• 💰 Use "tint" cans. Suitable for small parts (mirrors, handles) aerosol paints with precise color selection (for example, Motip).
• 💰 Rent equipment. A spray gun, IR dryer and polishing machine can be rented for 10–15% of the purchase price.
• 💰 Practice on unnecessary parts. Before painting the bumper, practice on an old door or hood - this will help hone your technique.

Savings on materials often come at a cost double costs. For example, cheap primer may shrink after a year, and you will have to repaint the part. Optimal balance - buy middle price segment (for example, Vika or Novol) and strictly follow the technology.

FAQ: Answers to frequently asked questions

Is it possible to paint a part without primer?

Technically possible, but the paint will last no more than a year. The primer provides adhesion and protection against corrosion. Exception - local touch-up chips with special pencils (for example, Touch-Up), where the soil is already included.

How to choose paint color by VIN code?

VIN code gives base color code, but the shade may vary due to fading of the original paint. For an accurate selection:

1. Find the color code on a decal (usually on the door pillar or under the hood).
2. Order paint from an authorized dealer or a trusted store (for example, Autocolor).
3. Compare the shade on unburned part (for example, under the hood).

For a perfect match, use spectrophotometer (available in large car service centers).

How many layers of paint and varnish should I apply?

Optimal scheme:

• 🔹 Base (for metallics): 2–3 layers.
• 🔹 Varnish: 2 layers (the first is “fog”, the second is full).

More layers does not mean better - too much paint can lead to drips or a long drying time. The main thing is uniform application.

How to paint a part without a spray gun?

Perhaps, but the quality will be worse. Alternatives:

• 🔹 Aerosol cans. Suitable for small parts. Apply from a distance 20–30 cm in 3–4 layers.
• 🔹 Brush. Only for primer or local touch-up. It is not recommended to apply paint with a brush - marks will remain.
• 🔹 Sponge. To create a “chameleon” or mother-of-pearl effect (for example, on moldings).

For large parts (hood, fender) a spray gun is required.

How long after painting can I wash my car?

Depends on the type of paint and drying conditions:

• 🔹 Acrylic system (base + varnish): You can wash it after 7–10 days (full polymerization takes up to 30 days).
• 🔹 Alkyd enamel: In 3–5 days.
• 🔹 Waterborne paint: After 14 days (takes longer to gain strength).

In the first 2 weeks, avoid automatic car washes and aggressive chemistry (e.g. bitumen removers).