Painting a car is a process where every little detail affects the final result. One of the key stages is preparing the varnish for application. An improperly diluted product can result in streaks, a dull finish, or even peeling of the finish after a few months. In this article we will look at how to dilute car polish depending on its type, working conditions and desired effect, and we will also cut professional secrets, which are rarely mentioned in standard instructions.
Many beginners believe that it is enough to simply mix varnish with solvent in an arbitrary proportion - but this is a grave mistake. The consistency of the composition depends on the room temperature, humidity, type of spray gun and even brand of varnish. For example, acrylic varnishes require one approach, and urethanes - completely different. We will analyze all the nuances in detail so that your coating turns out glossy, durable and without defects.
Types of car varnishes and their features
Before we talk about proportions, you need to understand what kind of varnish you are working with. There are three main types on the market, and each requires an individual approach to dilution:
- 🔹 Acrylic varnishes - the most common among beginners. Easy to apply, dry quickly, but less resistant to mechanical damage. Requires dilution special acrylic solvents (for example, P812-60 from PPG).
- 🔹 Urethane (2K) varnishes - professional choice. They give a deep gloss and high wear resistance, but are toxic and require strict adherence to proportions. Diluted urethane thinners (for example, Sikkens Autoclear LV).
- 🔹 Cellulose varnishes - an outdated type, but still found in the restoration of retro cars. Diluted nitrosolvents (for example, R-646), but require special care due to high volatility.
Important: do not mix different types of solvents! For example, acrylic thinner in a urethane varnish will cause the finish to become cloudy. Always check the label or material data sheet for compatibility.
Also note varnish class:
- HS (High Solid) — highly filled varnishes with minimal solvent content. They require precise proportions (usually 2:1 with hardener and 10-20% thinner).
- MS (Medium Solid) — universal varnishes, diluted in a ratio of 4:1:1 (varnish:hardener:thinner).
- LS (Low Solid) - outdated varnishes with a high solvent content. Almost not used in modern car repair.
Basic proportions of varnish dilution: table for different conditions
The proportions depend not only on the type of varnish, but also on the temperature in the spray booth. Below is a table with recommended ratios for the most popular brands. The data is relevant for spray gun with nozzle 1.3–1.4 mm and pressure 2–2.5 atm.
| Varnish type | Temperature, °C | Proportion (varnish:hardener:thinner) | Recommended thinner |
|---|---|---|---|
| Acrylic HS | 18–22 | 2:1:0.5–1 | PPG D8120, Sikkens Thinner 208 |
| Urethane 2K | 20–25 | 4:1:1–1.5 | DuPont 390S, Spies Hecker 560-50 |
| Acrylic MS | 15–18 | 4:1:1.5–2 | Mobihel Thinner 440-40 |
| Cellulose | 20–24 | 1:0.5:1 | R-646, R-647 |
Critical error: ignoring temperature! If the room is colder than +15°C, the varnish will take too long to dry, and at +30°C and above, it may “boil” and lose its gloss. In such cases, adjust the proportions of the thinner:
- 🌡️ Below +15°C: Increase the thinner ratio by 10-15% (eg instead of 4:1:1 use 4:1:1.5).
- 🔥 Above +25°C: Reduce thinner by 10% or use a "slow" thinner (e.g. Sikkens Thinner 202 for hot weather).
Warm the varnish and hardener to room temperature (20–22°C) before mixing. Cold components can cause uneven hardening and “shagreen” on the surface.
Step-by-step instructions: how to dilute spray gun varnish
Even knowing the proportions, many make mistakes at the mixing stage. Follow this algorithm to avoid problems:
- Prepare your tools: clean measuring containers, stirring sticks, sieve 120–150 microns for filtration, gloves and a respirator (especially for urethane varnishes!).
- Measure out the varnish. Use measuring cup with divisions. For example, for a ratio of 4:1:1 per 200 ml of varnish you will need 50 ml of hardener and 50 ml of thinner.
- Add Hardener. Mix the varnish with the hardener for 1–2 minutes in a circular motion, avoiding the formation of bubbles.
- Enter diluent. Add it gradually, continuing to stir. The consistency should resemble liquid honey.
- Filter the mixture through a sieve into the spray gun. This will remove any possible lumps or air bubbles.
The mixture is homogeneous, without lumps or separations |
Viscosity tested with a viscometer (18-22 sec for most varnishes)|
The color of the varnish did not change after mixing (darkening or cloudiness is a sign of incompatibility)|
The temperature of the mixture and the spray gun is the same (20–22°C)
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⚠️ Attention: Never use acetone or white spirit for diluting car polishes! These solvents are aggressive and destroy the structure of the varnish, leading to cracks and peeling. Suitable for acrylic varnishes only special acrylic thinners, and for urethane - urethane.
Common mistakes and how to avoid them
Even experienced painters sometimes make mistakes when thinning varnish. Here are the most common ones and ways to prevent them:
- 💧 Varnish is too thin → drips and low hiding power. Solution: use a viscometer (eg DIN-4) to control viscosity. The optimal expiration time is 18–22 seconds at 20°C.
- 🧊 Cold components → uneven hardening, “shagreen”. Solution: keep the varnish, hardener and thinner in a warm room for 12–24 hours before mixing.
- ⏳ Exceeding the pot life of the mixture → the varnish begins to thicken right in the spray gun. Solution: Urethane varnishes last 4–6 hours, acrylic varnishes last up to 8 hours. Do not prepare the mixture in reserve!
- 🔀 Incompatible components → cloudiness, peeling. Solution: always use materials from the same manufacturer (for example, varnish Sikkens Autoclear + thinner Sikkens Thinner).
What to do if the varnish has already begun to thicken in the spray gun?
If the mixture begins to polymerize, do not try to dilute it with additional solvent - this will disrupt the chemical composition. Better pour out the remains, rinse the spray gun special cleaner (for example, Gun Wash) and prepare a new batch of varnish.
⚠️ Attention: If after application the varnish remains sticky after 24 hours, this is a sign lack of hardener or incorrect diluent. This can only be corrected by sanding and repainting - “after-treatment” with a solvent will not help!
How to check the viscosity of varnish without a viscometer
Not everyone has a professional viscometer in their garage, but you can check the viscosity using improvised methods:
- Stick method: Dip a clean wooden stick into the varnish and lift it up. The mixture should drain uniform stream, and not drip or “tear”. The optimal speed is 3-4 drops per second.
- Glass test: Apply a drop of varnish onto the glass at a 45° angle. A well-diluted varnish will spread 3–5 cm without drips.
- Test Spray: Set the spray gun to minimum pressure (1.5 atm) and spray the varnish onto the cardboard. The optimal “torch” is a smooth oval without splashes.
If the varnish is too thick, add thinner drop by drop (no more than 5% of the total volume), stirring thoroughly after each serving. If it is too liquid, let some of the solvent evaporate (leaving the container open for 10–15 minutes) or add fresh varnish in a 1:1 ratio.
The ideal viscosity of the varnish depends on the type of spray gun: HVLP requires a thinner mixture (flow time 16-18 seconds), and traditional guns require a thicker mixture (20-22 seconds).
Choosing a thinner: which one is best for your varnish
The solvent is no less important a component than the varnish itself. It affects drying speed, gloss and even the color of the coating. Here are the key selection criteria:
- 🌡️ Temperature:
- Fast thinners (for example, Sikkens Thinner 206) - for operation at +15–20°C.
- Average (PPG DT870) - for +20–25°C.
- Slow (DuPont 390S) - for heat above +25°C.
- 🔬 Chemical composition:
- For acrylic varnishes - thinners based on esters and ketones.
- For urethane - mixtures with aromatic hydrocarbons.
- 🎨 Effect on gloss:
- High quality thinners (for example, Spies Hecker 560-50) give a deeper shine due to uniform spreading.
⚠️ Attention: Cheap thinners (for example, R-646 for acrylic varnishes) can cause yellowing of the coating in 1–2 years. For light and metallic colors, use only colorless thinners marked “for light colors”.
Pro tip: If you dye metallic or mother of pearl, choose thinners marked “high flow"(for example, Sikkens Thinner 208). They improve spreadability and prevent the “orange peel effect”.
Professional advice: secrets of perfect coverage
Experienced painters share tricks that are rarely mentioned in instructions:
- 💡 Two-layer application: Apply the first layer (“wet on wet”) with a dilution of 1:1:1, the second (after 10–15 minutes) - thicker (1:1:0.5). This will give depth and eliminate micropores.
- 🌬️ Humidity control: When humidity is above 60%, add to thinner antisilicone (for example, 3M Anti-Silicone) - this will prevent the formation of craters.
- ☀️ Drying with light: Use infrared lamps for uniform polymerization. But keep them at a distance of 50–70 cm to avoid local overheating.
- 🔄 Cross application: Spray the first coat horizontally, the second coat vertically. This eliminates streaking and improves traction.
Another professional life hack: if you work with matte varnish, dilute it 10% less than gloss. Matte finishes are less fluid, and excess solvent will lead to drips.
FAQ: Frequently asked questions about thinning varnish
Can varnish be diluted with water?
No, water is not compatible with car polishes. It causes delamination and corrosion of the metal under the coating. For water-soluble varnishes (e.g. PPG Envirobase) are used special water thinners, but this is a separate category of materials that does not belong to standard 2K varnishes.
What happens if you don't add a hardener?
The polish will remain soft and sticky even after several days. It will not gain strength and will wear off when washed. This can only be corrected by completely removing the coating and repainting.
How to store diluted varnish?
Diluted varnish with hardener cannot be stored - it begins to polymerize immediately after mixing. Maximum usage time:
- Acrylic varnishes: 6–8 hours.
- Urethane: 4–6 hours.
Prepare only the amount you have time to use.
Is it possible to mix varnishes from different manufacturers?
Theoretically, it is possible, but only if they are of the same type (for example, both acrylic HS) and are compatible in chemical composition. However risk of clouding or peeling very high. To ensure quality, use varnish, hardener and thinner one brand.
Why did the varnish run after painting?
Causes of leaks:
- The varnish is too thin (the proportion of thinner has been exceeded).
- High pressure in the spray gun (more than 2.5 atm).
- Applying too thick a layer in one pass.
- High room temperature (above 30°C).
Correct by sanding P1200–P1500 and polishing.