If, after applying the first layer of auto enamel, smudges, and the spray gun began to “spit” lumps - the problem is improper dilution of the paint. Even professional Sikkens or Mobihel require precise adjustment of viscosity before painting, otherwise the result will be spoiled. Solvent 646, which many people use “out of habit,” is not suitable for all types of paintwork: it can make acrylic paints too liquid, and metallic paints will require a specialized thinner with a drying retardant.

This article provides specific proportions for dilution base paints, varnishes and primers for different tools (HVLP spray gun, brush, spray can), as well as solvent compatibility table with popular brands (DuPont, PPG, Spies Hecker). We’ll separately look at why you can’t dilute car enamel with acetone or white spirit, and what to do if the paint has already thickened in the can.

1. Why car paint needs to be thinned: the physics of the process

Automotive enamels in original packaging have viscosity 80–120 DIN (by viscometer), whereas for high-quality spraying with a spray gun you need 18–22 DIN. Without dilution:

  • 🔴 The paint goes on in lumps due to high density (especially important for metallics and “mother of pearl”).
  • 🔴 Spray gun nozzle gets clogged, which leads to an uneven layer and increased material consumption.
  • 🔴 On vertical surfaces (doors, counters) formation smudgeswhich will have to be polished.

The solvent not only reduces viscosity, but also:

  • 🔹 Regulates drying time (important for working in a hot or cold workshop).
  • 🔹 Improves spreadability pigment on the surface.
  • 🔹Prevents shagreen formation (small craters) when drying.

Critical rookie mistake: dilute the paint “by eye”. For example, for acrylic two-component enamel from Standox Exceeding the solvent proportion by more than 10% of the norm leads to loss of gloss and reduced adhesion. The table below shows the exact proportions for different types of paintwork.

📊 What tool do you use to paint a car?
HVLP spray gun
Spray can
Brush
Airbrush

2. Types of solvents for car paint: which one to choose

All solvents for car enamels are divided into 3 groups by evaporation rate:

  1. Fast (for example, R-5, 647) - for operation at temperatures below +15°C.
  2. Universal (R-12, 646) - optimal for +18…+25°C.
  3. Slow (R-4, specialized for metallics) - at +25°C and above.

Important: solvent 646 only suitable for nitro enamels and some acrylic paints, but is absolutely not compatible with alkyd varnishes - they will become cloudy. For modern base paints (for example, PPG Deltabase) manufacturers recommend branded thinners, for example, PPG DT870.

Paint type Recommended solvent Proportion (paint:solvent) Application temperature
Acrylic 2K R-12, Sikkens Thinner 2020 2:1 (for spray gun) +18…+25°C
Metallic/pearl Spies Hecker 5600, R-4 1:1 (base) + 10% hardener +20…+30°C
Alkyd enamel 649, 650 3:1 (brush), 4:1 (spray gun) +15…+25°C
Primer R-646, DuPont 390S 4:1:1 (primer:solvent:hardener) +10…+30°C
⚠️ Attention: Never use acetone or white spirit for diluting car enamels. Acetone aggressively destroys pigments, and white spirit leaves a greasy film, which will cause the paint to peel off.

3. Dilution ratios for different instruments

The ratio of paint and solvent depends on application method:

🔫 HVLP spray gun

  • 🔹 Acrylic paint: 2 parts paint + 1 part solvent (R-12) + 10% hardener.
  • 🔹 Metallic: 1:1 (base: thinner) + 5% hardener (for Standox or Mobihel).
  • 🔹 Varnish: 2:1 (varnish:Sikkens Thinner 2030).

🖌️ Brush or roller

For manual painting, the paint is diluted less to avoid smudges:

  • 🔹 Alkyd enamel: 3:1 (paint:649).
  • 🔹 Acrylic: 4:1 + 5% hardener.

🎨 Spray can (aerosol)

If you poured the paint into the can yourself, use the proportion 1:1 (paint: solvent R-12) and add 10–15% propellant (for example, PPG D8120) for uniform spraying.

1. Check the room temperature (optimally +20…+22°C).

2. Filter the paint through a 190 micron mesh.

3. Add solvent in small portions, stirring with a mixer at 300–400 rpm.

4. Check the viscosity with a viscometer (should be 18-22 DIN for a spray gun).

5. Let the mixture sit for 10-15 minutes before applying.-->

4. How to dilute thickened paint in a jar

If the car enamel has dried out or become lumpy, it can be restored, but with reservations:

  1. Add solvent in small portions (5–10% of the volume of the jar), mixing thoroughly.
  2. Heat the jar to water bath up to +40…+50°C (not higher!).
  3. Filter via mesh 100–150 microns to remove lumps.

Critical moment: If paint is stored open for more than 6 months, its pigments may degrade. In this case, even after dilution, the color may change (for example, metallic "Silver" will turn dull gray). Always test reclaimed paint on a sample surface.

⚠️ Attention: Do not try to dilute dried two-component paint (2K) after mixing with the hardener - it polymerizes irreversibly. This mixture can only be disposed of.

5. Common mistakes when thinning paint

Even experienced painters sometimes make mistakes that spoil the result:

  • 🚫 Using the wrong solvent. For example, 646 for bases with chameleon effect leads to separation of pigments.
  • 🚫 Excess solvent content by more than 20%. The paint becomes too liquid, loses its coverage, and you have to apply 4-5 layers instead of 2-3.
  • 🚫 Ignoring temperature. If the workshop is +30°C, and you are using a “fast” solvent (R-5), the paint dries before it spreads - shagreen will appear.
  • 🚫 Poor mixing. This is especially critical for metallics: the pigments will settle to the bottom, and the first coat will be dull.
What to do if the paint has already been applied incorrectly?

If defects appear after painting due to improper dilution:

1. Smudges: Allow the paint to dry for 24 hours, then sand with P1200-P1500 waterproof sandpaper and polish.

2. Shagreen: Apply another coat of paint with the correct viscosity (18–20 DIN) or use a “wet” polish 3M 5901.

3. Matte: Cause: Excess solvent. It is necessary to varnish with a hardener (for example, Sikkens Autoclear LV).

4. Delamination: Remove the defective layer down to the primer and repaint with the correct thinner.

6. Thinners for specific paint brands

Manufacturers of paintwork often produce branded thinners, optimized for the chemical composition of their paints. The use of “foreign” solvents can lead to:

  • 🔴 Loss of shine (for example, DuPont ChromaBase with 646 instead of DuPont 390S).
  • 🔴Increasing drying time (relevant for PPG Envirobase).
  • 🔴 Changing the shade (critical for Spies Hecker Permahyd).
Paint brand Recommended thinner Features
Sikkens (Autowave, Autocryl) Sikkens Thinner 2020 (universal) For temperatures +15…+30°C. For metallics - Thinner 2030.
PPG (Deltabase, Envirobase) PPG DT870 (fast), DT875 (slow) Envirobase requires exact adherence to proportions (1:0.8).
Standox (VOC, Pro) Standox Thinner 360 For Standox VOC The thinner must be marked "VOC-compliant".
Mobihel (Helios) R-12 or Mobihel Thinner 2K For Helios with “pearl” effect - only branded thinner.

If you are painting a small part (mirror, bumper), buy small volume of proprietary thinner (0.5–1 l) instead of universal R-12. For example, for PPG Deltabase a bottle is enough PPG DT870 0.75 l - this is enough for 2-3 parts, and the quality will be higher than with a “station wagon”.-->

7. How to check paint viscosity without a viscometer

If you don’t have a viscometer at hand, use the “folk” method with stick or ruler:

  1. Dip a clean wooden stick into the paint.
  2. Lift it vertically: if the paint drips at a speed of 3–4 drops per second — viscosity is optimal.
  3. If drops fall less frequently, add solvent (5% by volume).
  4. If the paint flows in a stream, you have gone too far with the thinner; you need to let it sit for 10–15 minutes (part of the solvent will evaporate).

For a more accurate check, use glass test:

  • 🔹 Apply a drop of diluted paint onto the glass at an angle of 45°.
  • 🔹 If the drop spreads by 2-3 cm and does not form a “tail”, the viscosity is correct.
  • 🔹 If it doesn’t spread, add 5-10% solvent.
It is better to add less solventthan to pour. Paint with excessive viscosity can be brought to the desired consistency by adding more solvent. But you can’t save paint that’s too liquid—you’ll have to wait for it to evaporate or dispose of it.-->

FAQ: Frequently asked questions about car paint thinning

Is it possible to dilute car enamel with water?

❌ No. Water is not compatible with most car paints (except special water-soluble systems, for example PPG Aquabase). Even in them, water is added in strict proportions (usually no more than 10%) and only with branded additives.

How to dilute airbrush paint on a car?

For airbrush use specialized thinners with high fluidity, for example:

  • Createx Airbrush Reducer (for acrylic paints).
  • R-12 + 10% retarder (drying retardant).

Proportion: 1 part paint to 1 part thinner. The viscosity should be like milk.

Why did the paint become dull after thinning?

Reasons:

  • 🔹 Used incompatible solvent (for example, 646 for acrylic).
  • 🔹 The amount of solvent has been exceeded (>30% of the volume).
  • 🔹 The paint was applied in too thin a layer (less than 15 microns).

Solution: Apply 1-2 more layers with the correct viscosity or coat with gloss varnish.

How to dilute paint for painting plastic car parts?

For plastic (bumpers, moldings) use:

  • 🔹 Solvent with plasticizer (for example, PPG D8115).
  • 🔹 Proportion: 1 part paint + 0.5 parts thinner + 5% adhesive additive (for example, Sikkens Plastiprep).

⚠️ Without plasticizer, the paint will crack in 1-2 months.

How long can diluted paint be stored?

Lifespan of thinned paint:

  • 🔹 Without hardener: up to 7 days in an airtight container at +15…+20°C.
  • 🔹 With hardener (2K): no more than 4–6 hours (then irreversible polymerization begins).

To extend the life, store the jar in refrigerator at +5°C (but not lower!).