Car body repair is not only about restoring geometry and eliminating corrosion, but also about properly preparing the surface for painting. This is where choice comes to the fore. soil - a material on which paint adhesion, metal protection from rust and the durability of the entire paintwork depend. A mistake at this stage can result in paint peeling, blistering, or through corrosion within a few months.

There are dozens of types of primers on the market, and their classification often causes confusion even among experienced craftsmen. Some are designed for bare metal, others for plastic or previously painted surfaces. Still others combine the functions of anti-corrosion protection and filler. In this article we will look at all current types of primers for car repairs, their chemical composition, scope of application and nuances of application. We will pay special attention to compatibility with different body materials and typical mistakes that shorten the service life of the coating.

You'll find out why acid primers cannot be applied over acrylic primers, and epoxy primers require mandatory sanding before painting, how to properly combine layers for maximum protection and what new developments (for example, primers with zinc or graphite) are used by professionals in 2026. The information will be useful to both novice painters and car owners who want to control the quality of repairs in the service.

1. Acid (phosphating) soils: protecting metal from corrosion

Acid soils (also called reactive or poisonous) is the first layer of protection that is applied directly to bare metal. Their main task is to chemically bind to the surface, creating a thin film of phosphates or chromates. This film:

  • 🛡️ Blocks access to oxygen and moisture to metal, preventing oxidation;
  • 🔗 Improves adhesion subsequent layers (fillers, paint);
  • ⚡ Neutralizes residual rust on treated surfaces.

The compositions are divided into one-component (ready to use) and two-component (requires adding an activator). Popular brands: PPG DP40/DP40LF, 3M™ Scotch-Weld™, Novol Protect 340. Important: acidic soils are not fillers — their layer should not exceed 8–12 microns. After application, the surface must be washed with water to remove acid residues.

⚠️ Attention: Never apply acid primer over putty, old paint or acrylic primer! It will react with these materials, causing blistering and peeling of the coating. Use it only on bare metal or sandblasted surfaces.

Application technology:

  1. Clean the metal from rust (mechanically or chemically).
  2. Degrease the surface antisilicon (for example, App W700).
  3. Apply a thin layer of acid primer (spray at 2–2.5 bar pressure).
  4. After 5-10 minutes (depending on the temperature), rinse off the residue with water.
  5. Dry the surface and apply the next coat (eg epoxy primer).
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To treat welds and pitting, use a canned acid primer (e.g. Body 960) - it allows you to apply the composition precisely without splashing.

2. Epoxy primers: universal insulation and adhesion

Epoxy primers are "isolators", which create a dense barrier between the metal and the external environment. Unlike acidic ones, they do not enter into a chemical reaction with the surface, but form a mechanically strong film. Their key advantages:

  • 🔒 High chemical resistance to fuels, oils and salts;
  • 🌡️ Heat resistance (withstands up to +120°C without destruction);
  • 🛠️ Compatibility with all types of paints and varnishes;
  • 🕒 Durability — do not lose their properties for 5–7 years.

Epoxy primers are one-component (for minor repairs) and two-component (professional systems). Examples: PPG K36, Sikkens Autoclear Plus, Mobihel Epoxy Primer. Application feature: after drying (1–2 hours at +20°C) the surface must be polished abrasive P320–P400 to improve adhesion of the next layer.

⚠️ Attention: Epoxy primers cannot be dried at temperatures above +60°C in the first 2 hours - this disrupts the polymerization process and leads to brittleness of the coating. Also avoid applying in a thick layer (maximum 50 microns), otherwise shrinkage cracks may occur.
Type of epoxy primer Drying time (20°C) Recommended layer thickness Application
Quick drying (for example, Spies Hecker Permasolid HS) 30–60 minutes 20–30 µm Local repairs, urgent work
Standard (for example, PPG DP401) 2–4 hours 30–50 µm Full body painting, anti-corrosion protection
Highly filled (for example, Sikkens Autowave) 6–8 hours 50–80 µm Leveling minor defects, replacing putty
📊 What type of soil do you use most often in repairs?
Acidic
Epoxy
Acrylic
Polyurethane

3. Acrylic primers: fillers and levelers

Acrylic primers (also called fillers or leveling primers) solve two key problems:

  1. Filling micro-irregularities after grinding (for example, scratches from P180 abrasive).
  2. Creating a perfectly smooth base for painting, reducing paint consumption.

Unlike epoxy primers, acrylic primers are not anti-corrosion - their function is purely mechanical. They are:

  • 🟢 One-component (for example, App Fill Primer) - for minor repairs;
  • 🟡 Two-component (for example, PPG K38) - for professional use;
  • 🔴 Highly filled (for example, Sikkens Autoclear 2K) - replace putty on large areas.

Application technology:

  1. Apply 2-3 layers with drying time between coats for 5-10 minutes.
  2. After complete drying (1-2 hours), sand the surface with P400-P600 abrasive.
  3. Degrease before painting.
⚠️ Attention: Acrylic primers cannot be applied to bare metal without a preliminary acid or epoxy coat! They do not protect against corrosion and can absorb moisture, accelerating rusting.

Degrease the surface with anti-silicone |

Sand off old paint/putty with P240–P320 abrasive |

Apply acid or epoxy primer (if working on bare metal)|

Dry the previous layer according to the manufacturer's instructions -->

4. Primers for plastic: features and errors

Plastic car parts (bumpers, spoilers, mirrors) require special primers due to the low adhesion of standard compounds. The problem is that plastic:

  • 🧴 Has a smooth, non-porous surface;
  • 🔥 Can be deformed by solvents in ordinary soils;
  • ⚡ Accumulates static electricity, attracting dust.

Solution - adhesive primers (for example, PPG Adhesion Promoter, 3M™ Scotch-Weld™ Plastic & Paint Prep). They contain special additives that:

  • 🔗 "Stick" to plastic at the molecular level;
  • 🛡️ Protect from cracking due to temperature changes;
  • 🎨 Provide compatible with acrylic paints.

Typical mistakes when working with plastic:

  • ❌ Using regular acrylic primer without adhesive - the paint will peel off in 1-2 months.
  • ❌ Applying too thick a layer can cause “shrinkage” and cracks.
  • ❌ Neglect of degreasing - even fingerprints worsen adhesion.
How to determine the type of plastic before priming?

Most plastic car parts are marked on the back:

- PP (polypropylene) - requires a mandatory adhesive primer;

- ABS — can be primed with standard acrylic compounds after treatment with an antistatic agent;

- PUR (polyurethane) - requires special primers for elastic materials.

If there are no markings, do a test: apply a drop of soil to an inconspicuous area. If after 10 minutes no swelling or cloudiness appears, the composition is suitable.

5. Polyurethane and specialized primers

For specific tasks in auto repair, highly specialized primers are used:

Polyurethane primers (for example, Sikkens Autowave PU) combine the properties of epoxy and acrylic:

  • 🛡️ Anti-corrosion protection;
  • 🔧 Surface leveling;
  • 🌡️ Resistance to high temperatures (up to +150°C).

They are often used for repair of hoods and fenders, where increased resistance to mechanical loads is needed.

Soils with zinc (for example, Novol Protect 310 Zn) contain up to 90% zinc powder. They create cathodic protection: even if the coating is damaged, zinc “sacrifices” itself, protecting the steel from rust. Used for:

  • 🚗 Repair of thresholds and bottom;
  • 🔧 Weld seam treatments;
  • 🛠️ Restoring heavily corroded areas.

Primers for aluminum (for example, PPG DP40LF) contain special inhibitors that prevent the oxidation of light alloys. Mandatory when repairing aluminum parts (for example, hood Audi A8 or wings Jaguar XE).

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Polyurethane primers cannot be sanded “wet” (with water) - this disrupts their structure. Use only dry sanding with P400–P500 abrasive.

6. How to choose soil: step-by-step algorithm

The choice of soil depends on surface material, degree of damage and type of paint. Follow this algorithm:

  1. Define material:
    • 🚗 Steel/iron → acid + epoxy/polyurethane;
    • 🔳 Aluminum → specialized primer for light alloys;
    • 🟠 Plastic → primer-adhesive + acrylic;
    • 🔄 Old paint → acrylic filler (after sanding).
  2. Assess the degree of corrosion:
    • 🔴 Rust through → zinc primer + epoxy;
    • 🟡 Surface corrosion → acidic soil;
    • 🟢 No rust → epoxy or acrylic.
  • Consider the type of paint:
    • 🎨 Acrylic enamel → any compatible primer;
    • 🔥 Powder paint → epoxy primer;
    • ⚡ Metallic/pearl → highly filled acrylic for perfect smoothness.

      • Examples of combinations for typical cases:

      Situation Recommended primer scheme Examples of materials
      Local repair of a weld on a steel wing Acid → epoxy → acrylic filler Body 960 → PPG K36 → Sikkens Autoclear
      Painting a plastic bumper Primer adhesive → acrylic filler 3M™ Plastic & Paint Prep → App Fill Primer
      Restoring a rusty threshold Zinc primer → epoxy → polyurethane Novol Protect 310 Zn → PPG DP401 → Sikkens Autowave PU

      7. Common mistakes and how to avoid them

      Even professionals sometimes make mistakes when priming. Here TOP-5 critical misses and their consequences:

      1. Applying acid primer over acrylic

        ❌ What's happening: Acid corrodes acrylic, causing bubbles and peeling.

        ✅ How to avoid: Always apply acid primer first layer onto bare metal.

      2. Ignoring interlayer drying

        ❌ What's happening: Solvents do not have time to evaporate, which leads to the paint “boiling” during drying.

        ✅ How to avoid: Follow the drying time between coats (indicated on the can).

      3. Sanding epoxy primer with too coarse abrasive

        ❌ What's happening: Deep risks appear under the paint, spoiling the appearance.

        ✅ How to avoid: Use an abrasive no rougher than P400 for epoxy primers.

      4. Operating in low temperature or high humidity conditions

        ❌ What's happening: The primer does not polymerize, remains sticky or cracks.

        ✅ How to avoid: Optimal conditions: +18–25°C, humidity <60%.

      5. Savings on degreasing

        ❌ What's happening: Grease stains appear under the paint, adhesion deteriorates.

        ✅ How to avoid: Use antisilicone (for example, App W700) before each layer.

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    Before applying the primer, check the pressure in the spray gun: for acidic primers - 2.0–2.5 bar, for acrylic primers - 2.5–3.0 bar. Too high a pressure results in excess fog and material loss.

    8. Latest technologies: what the market offers in 2026

    Manufacturers of paints and varnishes are constantly improving primers, adding new properties to them. The following innovations are relevant in 2026:

    Primers with graphite (for example, PPG Envirobase Graphite Primer):

    • 🔋 Conduct electricity, which eliminates static stress on plastic parts;
    • 🛡️ Increases resistance to chipping by 30–40%;
    • 🌍 Contains up to 20% recycled materials (eco-certificate EcoLabel).

    Self-healing soils (for example, Axalta Cromax Pro Self-Healing):

    • 🔄 Fill microcracks when heated (for example, under the sun);
    • 🕒 Extend service life coverage for 2–3 years;
    • 💧 Reduce the risk of corrosion in places of chips.

    Primers with UV protection (for example, Sikkens Autowave UV):

    • ☀️ Absorbs up to 95% of ultraviolet radiation, preventing paint fading;
    • 🌡️ Reduces surface heating by 10–15°C;
    • 🎨 Maintain color saturation 20–25% longer.

    Also gaining popularity water-soluble soils (for example, PPG Aquabase) that reduce VOC (volatile organic compound) emissions by 60–70%. They are mandatory for services operating according to environmental standards Euro 6+.

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    Primers with graphite cannot be applied to aluminum - this causes galvanic corrosion. For light alloys, use specialized compounds without carbon additives.

    FAQ: Answers to frequently asked questions

    Is it possible to apply primer over old paint without sanding?

    No, this is a grave mistake. The old paint should be must be polished abrasive P240–P320 to ensure adhesion. The exception is if you use adhesive primer (for example, PPG Adhesion Promoter), but even in this case the surface must be degreased and matted with Scotch Brite.

    How many layers of primer should be applied?

    The number of layers depends on the type of soil:

    • Acidic: 1 thin layer (8–12 µm);
    • Epoxy: 1–2 layers (total thickness up to 50 microns);
    • Acrylic filler: 2–3 layers (until the surface is completely leveled).

      • Important: each layer must dry before applying the next (usually 5–15 minutes at +20°C).

    What primer is best for bumper repair?

    For plastic bumpers use two-stage system:

    1. Primer adhesive (for example, 3M™ Plastic & Paint Prep);
    2. Acrylic filler (eg PPG K38).

    If the bumper is from polypropylene (PP), be sure to use primer marked "for PP" - ordinary adhesives will not work.

    Can I paint directly over epoxy primer without sanding?

    No! Epoxy primer has a smooth surface and the paint will not adhere. His be sure to polish abrasive P400–P500 before painting. The exception is if you use epoxy primer with matt effect (for example, Sikkens Autoclear Plus), but even in this case, light sanding with Scotch Brite is recommended.

    What is the difference between spray primer and professional primer?

    Primers in cans (for example, Body 960, Kudo) are inferior to professional ones in three respects:

    • Layer thickness: It is difficult to apply evenly from a spray can;
    • Durability: professional primers last 1.5–2 times longer;
    • Adhesion: simplified formulas are often used in cans.

    However for local repairs (for example, chips on the hood) they are quite suitable.