The question of whether it is necessary to matte the paint before applying varnish on a car causes heated debate even among professionals. Some argue that this is a mandatory step, without which the varnish will simply “peel off” in a year. Others consider the procedure redundant for modern materials. Where is the truth?

In fact, the answer depends on a whole range of factors: the type of paint, the operating conditions of the machine, the chosen painting technology and even the climatic characteristics of the region. In this article we will look at physical principles of adhesion, let's analyze LKP manufacturers recommendations (liquid paints and varnishes) and show how improper matting can ruin even perfectly applied paint. And we’ll also reveal the secret of "dry matting", which not all painters know about.

Spoiler: in 80% of cases, mating is really necessary, but there are 3 situations when it can (and even should!) be skipped. Which ones exactly - read on.

What is matting and why is it needed?

Matting is the process of creating micro-roughness on the paint surface to improve adhesion to the varnish. In a professional environment, this stage is also called “interlayer grinding.” The main goal is to remove gloss from paint, which is formed due to:

  • 🔬 Shrinkage of paint when drying (especially important for acrylic systems)
  • 💨 The effects of solvents in paint that “pull out” the top layer
  • 🌡️ Temperature changes during drying (leads to “glassing” of the surface)

Without matting, the varnish is applied to a surface that is too smooth, which can lead to:

  • 🚗 Peeling varnish after 1-2 years (especially in places with high loads - hood, bumper)
  • 💧 "Fish Eye" - a defect when the varnish collects in drops due to poor spreadability
  • 🌞 Cloudiness of varnish under UV rays (due to microvoids between layers)

Interesting fact: in Japan and Germany matting before varnish is considered a mandatory step even for factory painting, whereas in USA Many workshops save on this by using “self-etching” varnishes. However, warranty return statistics show that American cars are 3 times more likely to require repainting due to problems with the varnish.

📊 Do you matte the paint before varnish?
Always, no exceptions
Only for metallics
Only if the paint is old
Never, the varnish stays on
I don't know what it is

When mating is MANDATORY (3 critical cases)

There are situations where skipping matting is guaranteed to lead to defects. Here they are:

  1. Metallics and pearls. Aluminum powder in such paints tends to “float” to the surface, creating a mirror effect. Without matting, the varnish will simply “slide off” this layer. Particularly critical for "Candy" series paints (for example, House of Kolor Kandy Apple Red).
  2. Repainting of individual elements. If you are only painting the bumper or fender and the rest of the body is covered with old varnish, the difference in gloss will result in a visible border after varnishing. Matting neutralizes this effect.
  3. Using "fast" paints. Rapid drying formulations (e.g. PPG Envirobase High Performance) form a super-smooth film. Without matting, the varnish may begin to bubble after 3-6 months.

Professional life hack: to check the need for matting, do the tape test. Stick a piece of masking tape to the dry paint and tear it off sharply. If there are paint particles left on the tape, matting is a must! If not, you can do without it (but with reservations, which are discussed below).

💡

For metallics, use an abrasive. P1200-P1500 — it retains glitter, but removes gloss. Suitable for solid colors P800-P1000

When matting is NOT NECESSARY (and even harmful)

Yes, there are cases when mating is not only useless, but can also worsen the result:

Situation Why you shouldn't mate Risks of matting
Usage 2K varnishes with high adhesion (for example, Sikkens Autoclear LV) Contains special additives for adhesion to smooth surfaces Matting can disrupt the chemical bond between the varnish and the paint.
Applying varnish "wet on wet" (within 15-30 minutes after painting) The paint does not have time to form a gloss The abrasive will clog the pores of undried paint.
Working with matte paints (for example, RAL 9005 Jet Black Matt) They initially have a rough surface Matting will make the surface too porous

Important: even in these cases, the paint surface must be perfectly clean. Any traces of silicone, wax or grease will negate all the benefits of “matte-free” technology. To clean, use anti-silicone degreasers (for example, 3M General Purpose Adhesive Cleaner).

What happens if you rewind the paint?

Excessive matting (with abrasive coarser than P600) leads to:

- Increased varnish consumption by 20-30% (due to high porosity)

- Risk of varnish subsidence after 1-2 years (due to too deep scratches)

- Visible “shagreen” even after polishing

Correct matting technology: step-by-step instructions

If you decide to checkmate, do it according to all the rules. Here is a professional algorithm:

  1. Paint exposure. Minimum time before mating:
    • 🔴 For acrylic paints: 2-4 hours at 20°C
    • 🟡 For metallics: 6-8 hours (due to slow polymerization of glitter)
    • 🟢 For water-soluble paints: 12-24 hours (they release solvents longer)
  2. Choice of abrasive:
    • 🧽 For manual sanding: sandpaper 3M Trizact P1500 (does not leave deep scratches)
    • 🤖 For machine: grinding wheels Mirka Mirlon P1200 with a rigid base
  • Grinding technique:
    • 🔄 Movements are only criss-cross (not in circles!
    • 💧 Abundant moisture (water + 5% soap solution for lubrication)
    • 🧐 Pressure control: 0.5-0.7 kg/cm² (too much will lead to grinding to the ground)

    ☑️ Matting quality control

    Done: 0 / 4

    A critically important nuance: after matting, the surface must be be sure to degrease, but not with an ordinary solvent, but with a special composition for interlayer cleaning (for example, PPG DX330). A regular degreaser leaves a film that impairs the adhesion of the varnish by 15-20%.

    Common mistakes and how to avoid them

    Even experienced painters sometimes make mistakes when matting. Here are the top 5 most dangerous:

    1. Using an abrasive that is too coarse. For example, P800 instead of P1500 for metallics. This leads to:
      • 🔍 Visible scratches under the varnish (“cobwebs”)
      • 💸 Increase varnish consumption by 30-40%
      ⚠️ Attention! If you sanded the metallic with a coarser abrasive P1000, the glitter will “lie flat” and the color will lose depth. This can only be corrected by repainting.
    2. Matting on wet paint. If you start sanding earlier than 2 hours for acrylic or 6 hours for metallic, the following will happen:
      • 🧊 “Dumping” abrasive into soft paint
      • 🎨 Blurring boundaries between layers ("dirty color" effect)
  • Dry matting without water. This leads to:
    • 🔥 Overheating of the surface (the paint may “swell”)
    • 🌫️ Formed dust that clogs pores
      • ⚠️ Attention! When dry matting metallics, the glitter “burns” to the abrasive and the color becomes dull. To restore it you will have to polish the varnish with an abrasive. P3000 with pasta.

    Another common mistake is matting in direct sunlight. UV light speeds up the polymerization of the top coat of paint, making it too brittle to sand. Work in the shade or at temperatures no higher than 25°C.

    💡

    For metallics and pearlescents, use the “wet matte” method with constant moisture. This prevents the glitter from overheating and maintains color saturation.

    Alternative methods of preparation for varnish

    If for some reason matting is not possible (for example, the paint is too thin or you are working with heat-sensitive materials), there are 3 alternative ways to improve adhesion:

    1. Chemical etching. Special formulations (for example, PPG D8115 Adhesion Promoter) etch the top layer of paint, creating micro-roughness at the chemical level. Suitable for:
      • 🔴 Water-soluble paints
      • 🟡 Thermoplastic coatings

      Technology: apply a thin layer, leave for 5-10 minutes, remove excess with a lint-free cloth.

    2. Plasma treatment. Used in industrial environments (e.g. factories) BMW and Mercedes). Pros:
      • ⚡ Increases adhesion by 40%
      • 🌿 Eco-friendly (does not require chemicals)

    Minus: the equipment costs from 500,000 rubles, so it is not used in garage conditions.

  • Ultraviolet irradiation. Short-wave UV (254 nm) modifies the paint surface, making it more porous. Used for:
    • 🔵 High pigment base paints
    • 🟣 Fluorescent and chameleon paints

      • Important: irradiation time is no more than 30 seconds, otherwise the paint will begin to degrade.

    Interesting case: company Tesla At its factories, it uses a combination of plasma treatment and UV irradiation to prepare paint for varnish. This allows them to eliminate matting completely, reducing painting time by 18%.

    How to check the quality of preparation before varnishing

    Before applying varnish, be sure to perform 3 tests:

    1. Adhesion test:
      • 🧪 Apply varnish to a small area (you can use test spray)
      • 🕒 After 24 hours, try to pry off the varnish with a sharp object
      • ✅ If the varnish peels off in plates, the adhesion is poor, you need to rewind
      • ✅ If the varnish crumbles along with the paint, everything is fine
    2. Purity test:
      • 🔦 Light the surface at an angle of 15-20° with a halogen lamp
      • 🔍 If dust particles or hairs are visible, repeat blowing and degreasing
    ⚠️ Attention! Even one speck of dust 0.1 mm in size under the varnish will be visible as a bump 0.3 mm high after drying. It can only be removed by sanding the varnish.
  • Uniformity test:
    • 👓 Wear polarized glasses (used to check windshield washers)
    • 🌈 Look at the surface from different angles - uneven matting will be visible as rainbow spots

    Pro Tip: To check the quality of matting, use profilometer (for example, Mitutoyo SJ-210). Optimal roughness for varnish adhesion: Ra 0.3-0.5 µm. If the indicator is lower 0.2 µm - adhesion will be weak, higher 0.8 µm - the varnish may sag.

    FAQ: Frequently asked questions about matting before varnish

    Is it possible to matte paint a week after application?

    Technically it is possible, but there are some nuances:

    • 🔹 If the paint has completely polymerized (exposure 7+ days at 20°C), use an abrasive P2000 and work with minimal pressure
    • 🔹 For metallics it is better to use chemical matting (for example, 3M Scotch-Weld Adhesion Promoter), so as not to damage the glitter
    • 🔹 Before matting, be sure to check the paint for “tack”: stick the tape and tear it off sharply - if the paint does not peel off, you can sand it

    Important: there is no point in matting old paint (more than 1 month old) - its surface is already too hard to create high-quality adhesion. In this case it is better to apply adhesive primer (for example, PPG K36) before varnish.

    How to matte paint on vertical surfaces (pillars, arches)?

    For vertical surfaces use:

    1. Soft sanding sponges (for example, 3M Softback) - they follow the contours and do not leave bald spots
    2. Horizontal movements (from left to right, not from top to bottom) to avoid water drips
    3. Special holders for sandpaper with magnetic fastening (for example, Mirka Hand Pad)

    Secret: for arches use P1000 instead of P1500 — where adhesion is more important than perfect gloss, due to constant exposure to sand and dirt.

    What is the difference between matting acrylic and polyurethane varnish?

    Main differences:

    Parameter Acrylic varnish Polyurethane varnish
    Required roughness Ra 0.4-0.6 µm Ra 0.3-0.5 µm
    Max. time between matting and varnishing 12 o'clock 4 hours (polyurethane absorbs dust faster)
    Recommended abrasive P1000-P1200 P1500-P2000 (polyurethane is sensitive to deep scratches)

    Critical point: polyurethane varnishes cannot be applied to paint treated with silicone polishes - this will lead to complete loss of adhesion. For acrylic varnishes this is not so critical.

    Can I use an orbital sander for matting?

    It is possible, but with reservations:

    • ✅ Suitable for: large flat surfaces (hood, roof, trunk)
    • ❌ Not suitable for: stiffening ribs, panel joints, metallics with large glitter

    Machine settings:

    • 🔧 Speed: 3000-4000 rpm (higher - the risk of grinding to the ground)
    • 🔄 Eccentricity: 3-5 mm (less is not effective, more leaves marks)
    • 💧 Water consumption: 0.5-0.7 l/min (for cooling and washing off dust)

    Important: for an orbital machine, use special grinding wheels with velor base (for example, Mirka Net) to avoid clogging the abrasive with paint.

    What if scratches appear after matting?

    Algorithm of actions:

    1. 🔍 Rate the depth of the scratches:
      • If they do not reach the ground, you can fill them with varnish (apply 10-15% thicker than usual)
      • If it reaches the ground, you need to repaint the element
  • 🧴 For shallow scratches (up to 5 microns) use fill varnish (for example, Sikkens Autoclear Plus) - it has increased viscosity
  • 🔧 After varnishing, polish the surface with an abrasive P3000 with pasta 3M Perfect-it III for leveling
    • ⚠️ Attention! If the scratches are located on metallics, polishing the varnish can “erase” the glitter in these places, making the color uneven. In this case, it is better to repaint the element.