Acrylic paints have become the standard in automotive painting due to their durability, brightness and ease of application. However, even professionals sometimes face a problem: how to properly dilute the composition in order to get the perfect coating without smudges, shagreens or premature drying. Not only the appearance, but also the durability of the paint layer depends on the choice of solvent and compliance with the proportions.

In this article we will look at all the current methods of thinning acrylic paint for cars - from classic solvents to non-standard solutions for emergencies. You will learn what mistakes lead to coating defects, how to choose proportions for specific conditions (temperature, humidity), and why some “folk” methods can ruin the result. We will pay special attention to safety: not all solvents are compatible with acrylic compounds, and some combinations can damage the factory paintwork during local repairs.

The material will be useful for both beginners and experienced painters. We collected data from manufacturers' technical data sheets (PPG, Sikkens, Mobihel), surveys of professional colorists and results of independent tests. All recommendations are adapted to the conditions of garage repair - without expensive equipment, but with a guarantee of quality.

Why acrylic paint needs to be diluted: physics and chemistry of the process

Acrylic automotive paints are supplied in concentrated form for two reasons: savings on transportation and the ability to adapt to different application conditions. The viscosity of undiluted paint can reach 100-120 DIN (by viscometer), while for high-quality spraying through a spray gun you need 18-22 DIN. Without dilution, the composition will lay down in a thick layer, forming smudges and “orange peel”.

Three key processes occur during dilution:

  • 🔬 Viscosity reduction — solvent molecules penetrate between the particles of pigment and binder, making the composition more fluid.
  • ⚗️ Hardener activation — in two-component acrylics, the solvent accelerates polymerization, but should not interfere with the curing reaction.
  • 🌡️ Adjusting drying time — “slow” solvents prolong the “open time” of the paint, which is critical at high temperatures.

Important: acrylic paints are classified as physically drying out compositions (unlike alkyd, where a chemical reaction occurs). This means that the solvent must completely evaporate from the layer, leaving no traces. Wrong choice of solvent leads to:

  • 🚫 Matte finish - if the solvent evaporates too quickly, preventing the paint from spreading evenly.
  • 🚫 Bubbles and craters - when using solvents with a high content of oils or silicones.
  • 🚫 Peeling - if the solvent aggressively affected previous layers (primer, old paint).
📊 What type of acrylic paint do you use most often?
One-component (1K)
Two-component (2K)
Acrylic-urethane
Acrylic metallic
I don't know

Official solvents for acrylic paints: compatibility table

Manufacturers of paints and varnishes always indicate recommended solvents in technical data sheets (TDS). Ignoring these recommendations is the main cause of defects. Below is a compatibility table for popular brands of automotive acrylic paints (data valid for 2026):

Paint brand Recommended solvent Proportion (paint:solvent) Features
PPG (series Deltareflex) PPG DT870 or DX330 2:1 (base) / 4:1:1 (paint:hardener:solvent) Use for metallics DT870 with additive PPG DCU2021 (anti-silicone)
Sikkens (Autowave, Autocryl) Sikkens Thinner 2000 3:1 (base) / 4:1:1 (for 2K) For low temperatures (<15°C) add Sikkens Retarder 2001 (10% of volume)
Mobihel (Helios) Mobihel 2K-Thinner or Acryl-Verdünner 2:1 (base) / 1:1:0.5 (for repair work) For “hot” shops (>25°C) use Mobihel Slow Thinner
Duxone (series 2K Acryl) Duxone 2K Verdünner 4:1:1 (paint:hardener:solvent) Compatible with Duxone Basecoat Thinner for base layers
Vika (Acrylic-Premium) Solvent 646 (no more than 10%) or Vika Thinner 3:1 (for 1K) / 2:1:1 (for 2K) Solvent 646 speeds drying but reduces gloss

Critical error: using solvent R-12 or white spirit for acrylic paints leads to clouding of the layer and loss of adhesion. These solvents are only suitable for alkyd or oil-based compounds.

If you are working with base for varnish (for example, PPG Deltabase or Sikkens Autowave Basecoat), use specialized thinners for base coats. They contain additives that improve the spreadability of metal particles and prevent the formation of “tiger stripes” (tiger striping).

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Before completely diluting the paint, do a test: apply a drop of the diluted composition to the glass and let it dry. If a matte film remains after drying, the solvent is too aggressive or there is too much of it.

Alternative solvents: when to use and when not to use

In garage conditions, there is not always access to branded solvents. In emergency cases, alternative formulations can be used, but with strict restrictions. Here is a list of acceptable and prohibited options:

✅ Allowed alternatives (with reservations):

  • 🟢 Solvent 646 - only for one-component acrylic paints (eg Vika or Bosny). Maximum concentration - 10-15% on the volume of paint. Excess leads to dullness of the coating.
  • 🟢 Solvent 647 - a less aggressive analogue of 646, suitable for diluting base layers (but not for finishing 2K acrylics!).
  • 🟢 Isopropyl alcohol (90%+) - only for cleaning the spray gun or thinning waterborne acrylics (for example, PPG Envirobase). Proportion: no more 5% from volume.
  • 🟢 Acetone - exclusively for degreasing the surface before painting, but not for dilution! It cannot be added to paint.

❌ Prohibited solvents (risk of defects 90%+):

  • 🔴 White spirit — leaves a greasy film, the paint does not stick to the surface.
  • 🔴 Solvent — corrodes the acrylic binder, leading to peeling.
  • 🔴 Kerosene/gasoline - even in small doses causes yellowing and cracking.
  • 🔴 Solvent R-4 — too slow for acrylics, the paint will “creep” after application.

Warning: if you are using acrylic urethane paints (for example, Sikkens Autocryl Plus or PPG Concept), any alternative solvents are prohibited. These compounds require strictly branded thinners due to high sensitivity to chemical composition.

What happens if you mix acrylic paint with nitro paint?

When mixing acrylic and nitrocellulose paints, a chemical conflict occurs: nitro paint contains aggressive solvents (butyl acetate, ethyl acetate) that destroy the acrylic binder. The result is that the coating will bubble, crack and peel in 1-2 weeks. In addition, nitro paints dry due to solvent evaporation, and acrylics dry due to polymerization, which makes co-curing impossible.

Dilution proportions: how to calculate based on temperature and humidity

The standard proportions specified by the manufacturer are designed for ideal conditions: temperature 20-23°C and humidity 50-60%. In reality, the parameters often differ, and the proportions need to be adjusted. Here is the universal formula:



Solvent Volume = (Base Proportion) × (Temperature Coefficient) × (Humidity Coefficient)



Where:


- Basic proportion - from the technical map (for example, 2:1 for the base PPG Deltabase)


- Temperature coefficient:


- <15°C: 1.2–1.5 (needs a “slow” solvent)


- 15–25°C: 1.0 (standard)


- >25°C: 0.8–0.9 (you need a “fast” solvent)


- Humidity coefficient:


- <40%: 0.9 (solvent evaporates faster)


- 40–70%: 1.0


- >70%: 1.1–1.2 (humidity slows down evaporation)

Calculation example for Sikkens Autowave Basecoat at 30°C and 75% humidity:

  • Basic proportion: 3:1 (paint:solvent).
  • Temperature coefficient: 0.85 (since >25°C).
  • Humidity coefficient: 1.15 (since >70%).
  • Final volume of solvent: (1 part) × 0.85 × 1.15 ≈ 0.98 parts (round up to 1:1).

For two-component acrylics (2K) the formula becomes more complicated, since you also need to take into account the proportion of the hardener. Typical scheme:

Temperature Proportion (paint:hardener:solvent) Solvent type
<15°C 4:1:1 Medium/slow (PPG DX330)
15–25°C 4:1:0.5 Standard (Sikkens Thinner 2000)
>25°C 4:1:0.3 Fast (Mobihel Fast Thinner)
⚠️ Attention: At temperatures below 10°C It is not recommended to apply acrylic paints at all - polymerization slows down 3-4 times, and the solvent evaporates unevenly. If painting is unavoidable, use infrared heaters for local heating of the part up to 18-20°C.

Check the temperature in the paint booth (garage)|Use the same brand of solvent with the paint|Mix the paint thoroughly with a mixer (2-3 minutes)|Filter the composition through a 125 micron mesh|Make a test spray on a test panel-->

Thinning acrylic paint for different application methods

The method of paint application directly affects the required viscosity. Let's look at the three most common methods and their corresponding dilution proportions.

1. Spray gun (HVLP)

The most popular tool for car painting. Optimal viscosity for HVLP spray gun - 18-22 DIN (by viscometer DIN 4). Proportions:

  • 🔫 Base coat (metallic/pearl): 2:1 (paint:solvent). Use specialized thinner for bases (PPG DT870, Sikkens Basecoat Thinner).
  • 🔫 Acrylic 2K (finishing layer): 4:1:1 (paint:hardener:solvent). For HVLP it is better to reduce the pressure to 1.5-2 atm and use the nozzle 1.3–1.4 mm.

2. Brush or roller (for local repairs)

When applied by hand, the paint should be thicker so that smudges do not form. Viscosity - 25-30 DIN. Proportions:

  • 🖌️ One-component acrylic: 1:0.3 (paint:solvent). Add solvent gradually, controlling fluidity.
  • 🖌️ Two-component acrylic: 4:1:0.5. Apply in 2 thin layers at intervals of 15-20 minutes.
⚠️ Attention: When painting with a brush Do not use solvents with a high acetone content (for example, 646). They cause the top layer to dry out quickly, while the bottom layer remains liquid - this leads to wrinkling of the coating.

3. Airbrush (for details and artistic painting)

An airbrush requires the most liquid consistency possible - 12-15 DIN. Proportions:

  • 🎨 Basic acrylic: 1:1 (paint:solvent). Use special thinner for airbrush (Createx Airbrush Reducer).
  • 🎨 Acrylic with effects (chameleon, fluo): 1:1.5. These paints are thicker due to additives.

For all application methods the following rule applies: dilute the paint 10-15 minutes before use. If the diluted composition is left for a long time, the solvent will begin to evaporate, increasing the viscosity.

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For an HVLP spray gun, it is critical to maintain a balance between paint viscosity and air pressure. Too thin paint at high pressure (>2.5 atm) will give fog and loss of shine, and too thick paint will lead to shagreen.

Common mistakes when thinning acrylic paint and how to avoid them

Even experienced painters sometimes make mistakes that lead to defects. Here are the most common ones and ways to prevent them:

  1. Using expired solvent.

    Solvents have an expiration date (usually 12-24 months in a closed container). After opening the can, the period is reduced to 3-6 months. An expired solvent loses its volatile components, which leads to:

    • 🔹 Slow drying (the paint remains sticky for a day or more).
    • 🔹 Formation of matte spots due to uneven evaporation.

Solution: Buy solvents in small containers (0.5–1 l) and store them in a tightly closed container at a temperature 15–25°C.

  • Failure to follow the mixing sequence.

    When working with two-component acrylics first mix the paint with the hardener, and only then add the solvent. If you do the opposite, the hardener may curdle and the paint will become unusable.

    Solution: Follow the diagram:

    

    1. Paint + hardener → mix for 2 minutes
    

    2. Add solvent → stir for 1 minute
    

    3. Filter through a 125 micron mesh

  • Ignoring test paint.

    Even if you have calculated the proportions accurately, always do test spray on a test panel or piece of metal. This allows you to:

    • 🔹 Check the uniformity of spraying (if there are any “tails” or drops).
    • 🔹 Assess the drying speed (is it too fast/slow).
    • 🔹 Make sure there is no reaction with the soil (no bubbles or peeling).

    Another common mistake is thinning paint by eye. This is only permissible for experienced painters with extensive experience. Beginners are recommended to use measuring containers or electronic scales for precise dosing of components.

    📊 What mistake did you make when thinning acrylic paint?
    Didn't follow the proportions
    Used the wrong solvent
    Didn't do a test paint job
    Stored diluted paint for too long
    Other

    Thinning acrylic paint for specific applications

    Sometimes it is necessary to adapt the paint to non-standard conditions. Let's consider three such cases.

    1. Painting in high humidity conditions (>80%)

    At high humidity, solvent evaporates more slowly and water from the air can condense on fresh paint, causing cloudy spots or craters. Solutions:

    • 💧 Use "slow" solvent (PPG DX330, Sikkens Retarder 2001) in proportion 1:0.3 (paint: solvent).
    • 💧Add antifoam (PPG DCU2021) - 2-3 drops per 100 ml of paint.
    • 💧 Increase the temperature in the spray booth to 25-28°C (but not higher, otherwise the paint will dry too quickly).

    2. Local repair with transition (blending)

    When doing partial painting (for example, repairing a chip or scratch), it is important to ensure a smooth transition between the old and new coating. To do this:

    • 🎨 Thin the paint to first layer 10-15% stronger than usual (for example, 2:1.2 instead of 2:1). This will improve the spreadability.
    • 🎨 For transition layer use high solids thinner (Sikkens Blending Thinner).
    • 🎨 Apply paint with low blood pressure (1.2–1.5 atm) and increased distance (25–30 cm from the part).

    3. Painting plastic parts

    Plastic requires special handling, as many solvents cause it to soften or crack. Rules:

    • 🔧 Use only solvents for plastic (PPG D8105, Sikkens Plastic Thinner).
    • 🔧 Thin the paint 20-30% weaker than for metal (for example, 4:1 instead of 4:1.5).
    • 🔧Pre-apply adhesive primer (PPG DP40, Sikkens Autoprime Plastic).
    ⚠️ Attention: Never use solvent-based solvents on plastic. xylene or toluene - they destroy the structure of most automotive plastics (including bumpers made of PP or ABS).

    FAQ: Frequently asked questions about thinning acrylic paint

    Can acrylic paint be thinned with water?

    Only if this waterborne acrylic (for example, PPG Envirobase or Sikkens Autowave Hydro). Water is not suitable for standard acrylic paints - it does not mix with organic solvents and causes coagulation of pigments. The maximum water content in waterborne acrylics is: 10-15% (up to 30% can be used to clean the spray gun).

    Important: even for water-based paints, the water must be distilled and heated to 20-25°C, otherwise coating defects may occur.

    How to dilute acrylic paint if there is no proprietary solvent?

    As a last resort you can use solvent 647 (for one-component acrylics) or universal acrylic thinner (for example, Bosny Universal Thinner). Proportion - no more 1:0.5 (paint: solvent).

    There are no alternatives for two-component acrylics - only branded solvents. The use of substitutes will lead to incomplete polymerization and paint peeling.

    How do you know if the paint is diluted correctly?

    There are three ways to check:

    1. Viscometer: The viscosity should be 18-22 DIN for spray gun, 12-15 DIN for an airbrush.
    2. Glass test: A drop of paint should spread evenly, without breaks, in 10-15 seconds.
    3. Test Spray: There should be no tails, drops or uneven coverage on the test panel.

    If the paint runs off the glass too quickly (<5 seconds), it is over-thinned. If it doesn't spread at all, it's too thick.

    Is it possible to mix acrylic paint from different manufacturers?

    Theoretically it is possible, but highly not recommended. Different brands use different binders and pigments, which may react. If you still have to mix:

    • Use paints on same basis (for example, both on acrylic-urethane).
    • Mix no more 30% one color to another.
    • Add 10% universal acrylic thinner for stabilization.

    The best option is to do test paint and check compatibility after 24 hours (no bubbles, peeling or discoloration).

    How to store thinned acrylic paint?

    Store diluted paint it's impossible — it begins to polymerize immediately after adding the hardener (for 2K systems). Maximum period:

    • One-component acrylic: up to 24 hours in an airtight container at 15-18°C.
    • Two-component acrylic: no more 4-6 hours (even in the refrigerator).

    To extend life:

    • Store the container in refrigerator (but not below +5°C).