Painting a car is a process where the quality of the result depends 70% on the preparation of the materials. Even the most expensive two-component varnish from premium brands like PPG or Sikkens may disappoint if not properly diluted, filtered or stored before application. This article is not about how to paint a car (that’s a separate topic), but about how to turn a can of varnish into a perfectly ready-to-use composition - without bubbles, lumps and unpredictable reactions.
We will analyze the entire process: from choosing the type of varnish (acrylic, polyurethane, HS/MS) to the nuances of working with hardeners and solvents. We will pay special attention critical errors that lead to clouding of the varnish 2-3 months after painting - they are almost never mentioned in manufacturers' instructions. If you are painting a car for the first time or want to systematize your knowledge, everything is here, including component compatibility tables and checklists for self-control.
1. Varnish selection: which composition is suitable for your project
There are three main types of varnishes on the car enamels market, and each has its own pros, cons and applications. A mistake in choosing can cost not only money, but also time for rework.
Acrylic varnishes (for example, DuPont ChromaPremier) - the most budget option, but they quickly lose their gloss and turn yellow under UV rays. They should be used only for temporary work or painting internal parts (trunk, engine compartment). Polyurethane varnishes (type Spies Hecker Permahyd) - the golden mean: resistant to chemicals, durable, but require strict adherence to proportions when mixing. Finally, HS/MS varnishes (high solid/medium solid) from PPG Envirobase or Basf R-M - premium segment with high solids, which provides color depth and resistance to micro-scratches.
- 🔹 For full body painting: HS varnish (high solids, fewer layers)
- 🔹 For local repairs: MS varnish (easier to shade)
- 🔹 For classic cars: Polyurethane varnish (better conveys the “wet” effect)
- 🔹 To save money: Acrylic varnish (only for non-critical areas)
It is important to consider painting system. For example, varnishes PPG optimized for working with their own primers and base enamels. Mixing brands (for example, varnish Sikkens + hardener Mobihel) may result in delamination or clouding after 6-12 months. Always check compatibility using the manufacturer's data sheets.
2. Diluting varnish: proportions and secrets of professionals
Even a perfectly selected varnish will deteriorate if it is not properly diluted with hardener and solvent. There is no room for “by eye” - only precise proportions and control of conditions.
Standard ratio for most two-component varnishes: 2 parts varnish: 1 part hardener: 10-20% solvent (from the total volume of varnish + hardener). But this is the basic formula! The actual proportions depend on:
- 🌡️ Temperatures in the spray booth (below +20°C - add +5% solvent)
- 💨 Humidity (above 60% - use a “slow” solvent)
- 🔧 Equipment type (HVLP spray gun requires a thinner consistency)
- ⏳ Drying time (accelerators reduce it by 30%, but may cause film fragility)
Professionals use weight method dosage, not volume. The fact is that the density of hardeners and varnishes is different: 100 ml of hardener can weigh 110 grams, and 100 ml of varnish - 130 grams. Weigh ingredients on a kitchen scale to the nearest 1 gram. For example, for varnish Basf R-M Onyx HD proportion by weight: 100 g varnish + 50 g hardener + 15 g solvent R-M Thinner 830.
If you are working with varnish in a cold garage (+15°C or below), warm up the can of varnish in warm water (not higher than +30°C!) before mixing. This will reduce the viscosity and make filtration easier.
| Varnish type | Standard proportion (varnish:hardener:solvent) | Recommended solvent | Drying time at +20°C |
|---|---|---|---|
| Acrylic (eg Mobihel) | 2:1:0.5 | Universal 420-450 | 8-12 hours |
| Polyurethane (Spies Hecker) | 4:1:1 (by volume) | Permahyd Thinner 530 | 16-24 hours |
| HS-varnish (PPG Envirobase) | 3:1:0.8 (by weight) | DX380 or DX381 | 4-6 hours (at +23°C) |
| MS-varnish (Sikkens Autoclear) | 2:1:0.3 | Sikkens Thinner 208 | 12-18 hours |
⚠️ Attention: Never use xylene-based solvents for HS varnishes! They destroy the structure of the high-hardness resin, which leads to an “orange peel” appearance after the first layer. For such varnishes, only specialized thinners markedHSorUHS.
3. Varnish filtration: why it is critical and how to do it right
Unfiltered varnish is the main cause of painting defects: from small “specks” to full-fledged lumps that spoil the entire job. Filtration removes not only dust, but also microscopic clumps of resin that form during storage.
Use double filtration:
1. Primary - through metal sieve 120-150 microns (removes large particles).
2. Final - in disposable paper filter 5-10 microns (for example, 3M Paint Filtration Bag), installed in a paint funnel.
Don't skimp on filters! Cheap Chinese analogues often miss particles up to 20 microns in size, which leads to roughness of the varnish.
The filtration process must take place just before pouring into the spray gun. If the varnish sits in the container after filtration for more than 30 minutes, microbubbles may form in it again. Also avoid shaking the container with varnish - this saturates it with air, which will then appear in the form of craters on the surface.
Make sure that the jar of varnish has been in a warm place for at least 2 hours|Use a clean glass or metal funnel|Check the integrity of the filter (no breaks)|Filter slowly, without pressure|Immediately close the container with the filtered varnish-->
⚠️ Attention: If there are still bubbles in the varnish after filtering, let it sit for 10-15 minutes. Do not try to “blow out” the bubbles with compressed air - this will only increase foaming. To speed up the process, you can add 1-2 drops of an anti-silicone additive (for example, U-Pol Anti-Silicone).
4. Testing varnish before application: how to avoid surprises
Even if you followed the instructions exactly, always test the varnish before painting the main part. This will identify problems with viscosity, drying speed or component compatibility.
For the test use test plate (can be bought at auto chemical stores) or a piece of metal processed in the same way as a car body (soil, base). Apply 1-2 layers of varnish and evaluate:
- Spreadability: the varnish should lie smoothly, without “tails” from the spray gun.
- Unstuck time: 10-15 minutes after application, touch the surface with a dry cloth - it should not stick.
- Gloss: After complete drying (after 24 hours), the light reflection angle should be clear, without cloudy areas.
If the test layer shows defects, check:
- Whether the proportion of solvent is exceeded (leads to “sagging” of the varnish).
- Is it too cold in the room (below +18°C - the varnish may not spread).
- Is the hardener expired (shelf life after opening is 6 months).
Please note hardener color: If it turns yellow or cloudy, it cannot be used.
What to do if the varnish “stood up” (thickened) in the spray gun?
If the varnish begins to thicken while painting, immediately rinse the spray gun with a solvent (for example, Gun Wash) and clean the nozzle with a needle. Under no circumstances should you try to dilute the varnish directly in the spray gun tank - this will lead to uneven spraying. It is better to prepare a new batch of varnish by adjusting the solvent proportions (+ 10-15%).
5. Storage of varnish: how to preserve its properties until the next painting
Improper storage of varnish is not only a loss of money, but also the risk of ruining the next painting. Two-component varnishes, after mixing with a hardener, have limited lifespan (pot life): from 4 to 8 hours depending on temperature. But even unopened varnish deteriorates if the conditions are violated.
Basic storage rules:
- Temperature: +5°C to +25°C. Freezing leads to delamination, and overheating (above +30°C) leads to polymerization.
- Humidity: not higher than 60%. Jars should be stored in sealed plastic containers with silica gel.
- Light: UV rays destroy resins. Use opaque containers or darkened shelves.
- Position: banks must stand verticallyto avoid leaks under the lid.
If the varnish has been stored longer than 12 months, test it on a test plate before use. Old varnishes may lose their shine or appear yellow. To restore properties, some wizards add up to 5% fresh varnish of the same type, but this is a temporary solution - it’s better to buy a new jar.
| Varnish type | Expiration date (unopened) | Expiration date after opening | Signs of damage |
|---|---|---|---|
| Acrylic | 24 months | 6 months | Cloudiness, lumps, strong odor |
| Polyurethane | 18 months | 12 months | Yellowish, gel-like consistency |
| HS/MS varnish | 12 months | 6 months | Delamination, loss of gloss after test |
6. Common mistakes and how to avoid them
Even experienced painters sometimes make mistakes when preparing varnish. Here are the most common ones and how to prevent them:
- 🔴 Using expired hardener: The shelf life of the hardener is 6 months after opening. Expired hardener results in “soft” varnish that scratches when washed. Always label jars with the date they were opened.
- 🔴 Incompatible solvents: For example, using 646 solvent with HS varnish. This leads to clouding and cracking after 3-6 months. Always check the manufacturer's recommendations.
- 🔴 Violation of proportions "by eye": Even a 5% deviation in hardener can cause drying to be either too slow (dust sticking) or too fast (cratering). Use measuring containers or scales.
- 🔴 Ignoring Test Spray: A polish may look perfect in the can, but produce a "web" or bubble when sprayed. Always test on cuttings!
- 🔴 Storing mixed varnish: If you have diluted the varnish with hardener but have not used all of it, throw away the remainder. After 2-3 hours it begins to polymerize in the container, and repeated use will lead to clumps.
The error with cross contamination. For example, if you used the same measuring container for different brands of varnish and hardener, the residue may react. Always wash your tools acetone or a specialized cleaner (PPG DX330) after work.
The most common cause of varnish defects is not the varnish itself, but a violation of the microclimate in the paint booth. Optimal conditions: temperature +20...+23°C, humidity 40-50%, absence of dust and drafts.
7. Preparation of varnish for specific tasks
Sometimes standard recommendations are not suitable. For example, when painting plastic parts or working in extreme conditions, adjustments to the process are required.
Painting plastic (bumpers, spoilers):
- Use special plastic primers (PPG DP40) before varnish.
- Add to varnish plasticizer (up to 5%) for better adhesion.
- Dry at +60°C for 1 hour (otherwise the varnish may peel off after 2-3 months).
Painting in a cold garage (+10...+15°C):
- Increase the proportion of solvent by 15-20%.
- Use a “slow” hardener (e.g. Sikkens Activator 92660).
- Heat the part with an infrared heater to +18°C before application.
Painting "metallic" or "chameleon":
- Apply varnish in 3 thin layers instead of 2 standard ones, so as not to “drown” the effect of the base.
- Use a solvent with a high evaporation rate (Basf 3607) to prevent pigment from spreading.
For restoration of old paintwork (for example, after polishing) is suitable liquid glass or ceramic varnish (CarPro Cquartz). It does not need to be diluted - it is applied neat with a microfiber applicator.
FAQ: Answers to frequently asked questions
Can varnish be diluted with water?
No, water is not compatible with solvent-based car polishes. It causes cloudiness and separation. For water-soluble varnishes (e.g. PPG Aquabase) special water-based thinners are used, but they require special equipment (spray guns with Teflon seals).
What is the difference between HS varnish and MS varnish?
HS (High Solid) contains more solids (up to 70%), which allows you to apply fewer layers and reduces drying time. MS (Medium Solid) - more universal, with a dry residue content of 50-60%. HS gives a deeper shine, but requires precise adherence to technology (temperature, humidity). MS is easier to use for beginners.
Why did the varnish turn yellow a month after painting?
Yellowness is a sign of oxidation of resins under the influence of UV rays or improper polymerization. Reasons:
- Using cheap acrylic varnish without UV filters.
- Exceeding the proportion of hardener (accelerates the aging of the film).
- Drying at temperatures above +60°C (leads to destruction of resins).
To fix it, you need to polish the surface with an abrasive paste (3M 09374) or apply an additional layer of ceramic coating.
What is the best solvent for PPG varnish?
For varnishes PPG series solvents are recommended DX:
- DX380 - universal for HS varnishes.
- DX381 — “fast” for warm conditions (+25°C and above).
- DX330 - for cleaning equipment.
Do not use solvents from other brands (such as Mobihel), even if they are positioned as “universal”.
Is it possible to apply varnish without a base?
Technically it is possible, but it violates the technology. Varnish without a base coat will not have sufficient adhesion to the ground, which will lead to peeling. Exception - single-layer enamels (for example, PPG Deltacron), which already contain pigment and do not require a separate base. In other cases, the varnish is applied over the base color after 15-30 minutes (depending on the system).