High-quality car painting is not only the correct preparation of the surface and application of the base, but also the final chord, which is polishing and shine. varnish coating. It depends on how competently you prepare the working composition, whether the car body will shine with a mirror gloss or be covered with shagreen and matte spots. Many beginners underestimate the importance of precise adherence to proportions, believing that it will work “by eye”, however, two-component systems such as HS-varnish or MS-varnish, require mathematical precision.
The process of mixing components is a chemical reaction that cannot be stopped or corrected once polymerization has begun. If you make a mistake with the quantity hardener or you are using the wrong one solvent, the material may not dry, bubble, or, even worse, peel off after several months of use. In this article, we will look in detail at how to properly dilute paints, what tools to use, and how to avoid fatal mistakes that lead to redoing the entire job.
Before opening the jars, you need to make sure that all components are at room temperature (about 20°C). Cold varnish will have a different viscosity, and the proportions indicated on the can may not work correctly. It is also critical to have clean, dry measuring containers, as even a drop of water or old solvent can spoil the entire volume of the mixture, causing cloudiness or curdling of the mixture.
System components: varnish, hardener and solvent
Modern car varnishes are complex chemical compositions, where each element performs a strictly defined function. The basis is made by himself varnish concentrate, which contains resins that give the coating hardness, elasticity and shine. Depending on the dry matter content, varnishes are divided into HS (High Solid) and MS (Medium Solid). HS varnishes are thicker, give a thicker layer and are less prone to shrinkage, while MS varnishes are thinner and require more coats.
The second key component is hardener (or catalyst). Without it, the varnish will remain sticky and will never reach its final strength. Hardeners come in different reaction speeds: fast (for cold weather or drying without heat), normal (universal) and slow (for hot climates or large surfaces to have time to stretch the material). Using the wrong hardener is a common cause of shagreen or, conversely, smudges.
Third component - solvent (thinner). His task is to bring the mixture to a working viscosity so that it can be sprayed through the spray gun nozzle. It is important to understand: the solvent does not participate in the chemical curing reaction, it only evaporates. Therefore, its amount affects only the fluidity, but not the hardness of the final film. However, the choice of solvent type (fast, medium, slow) directly affects how the varnish will lay down and how much time you will have to work.
⚠️ Attention: Never use acetone or 646 thinner from a hardware store to thin expensive car clear coats. They may contain alcohols or water, which will react with the components of the varnish, causing irreversible clouding (whitish cast) immediately upon application.
When choosing materials, always try to use products from the same manufacturer. Varnish, hardener and solvent from different brands may have incompatible chemical formulas. For example, an aggressive solvent of one brand can “curl” the resin of another brand of varnish. If you work with products Mobihel, PPG or Body, it is best to purchase a branded “laxetap” kit (mixing kit), where the components are already perfectly selected.
Mixing ratios: gold standards
The most important stage is determining the correct proportions. They are always indicated on the label of the varnish can as a ratio, for example, 2:1 or 4:1. The first number indicates the number of parts of varnish, the second - the number of parts of hardener. The solvent is added separately as a percentage of the volume of the finished mixture or as needed until the working viscosity is achieved.
For most HS varnishes the standard is the proportion 2:1. This means that you need to take one part of hardener for two parts of varnish. If you measure out 500 ml of varnish, you will need 250 ml of hardener. For MS varnishes the following proportion is often found: 4:1, where 4 parts of varnish take 1 part of hardener. Violation of these proportions in the direction of increasing the hardener will make the coating brittle, and decreasing it will not allow it to completely harden.
Solvent is usually added in a volume of 5-10% of the total mass of the mixture, but the exact amount depends on the temperature in the spray booth and the settings of your spray gun. In hot weather, you can add a little more slow solvent so that the varnish has time to spread. In cold weather, on the contrary, they use a fast solvent and minimize its amount to speed up evaporation.
For accurate dosing, it is best to use graduated measuring cups. A scale is already applied to the walls of such glasses, allowing you to mix components without complex mathematical calculations. You simply pour the varnish to the desired mark, and then add hardener to the appropriate proportion mark.
Step-by-step instructions: how to breed correctly
The process of preparing the working mixture requires consistency and purity. First, open the can of varnish and stir the contents thoroughly, as heavy resins may have settled to the bottom. Then pour the required amount of varnish into a clean measuring cup. After this, add hardener in strict accordance with the proportion specified by the manufacturer.
☑️ Check before mixing
After adding the hardener, the mixture must be mixed again, but not so intensely as to avoid saturating it with air bubbles. And only at the very end, just before pouring into the spray gun tank, is it added solvent. The amount of solvent is adjusted “by eye” or by viscosity: the mixture should flow in an even stream, but not be too watery.
The finished mixture must be filtered through a funnel with a mesh filter (usually 125-190 microns). This will remove any dust that has gotten into the glass and any small clumps that may have formed during mixing. Filtration is a mandatory step to achieve perfect gloss without debris.
⚠️ Attention: The pot life of the finished mixture (Pot Life) is limited. After adding the hardener, you have 30 minutes to 2 hours (depending on the type of hardener) to use the varnish. After this, the mixture will begin to thicken and become unsuitable for painting, even if you add more solvent.
Viscosity table and spray gun settings
Properly diluted varnish should have a certain viscosity. A material that is too thick will not have time to spread, leaving shagreen ("orange peel"), while a material that is too liquid will flow in vertical stripes. To measure viscosity, professionals use a viscometer - a cup with a calibrated hole, but experienced painters often rely on the stream flowing from the stirrer.
Below is a table of approximate settings for different types of varnishes. Remember that the operating pressure at the spray gun head should be approximately 2-2.5 atmospheres, regardless of viscosity, but the nozzle diameter will vary.
| Varnish type | Proportion (Varnish:Hardener) | Nozzle diameter (mm) | Pressure (Bar) | Drying time between coats |
|---|---|---|---|---|
| HS Varnish (High Solid) | 2:1 | 1.3 - 1.4 | 2.0 - 2.5 | 15-20 min |
| MS Varnish (Medium Solid) | 4:1 | 1.4 - 1.6 | 2.5 - 3.0 | 10-15 min |
| UHS Varnish (Ultra High) | 3:1 or 4:1 | 1.3 - 1.35 | 2.0 - 2.2 | 20-30 min |
| Matt varnish | 2:1 | 1.5 - 1.7 | 2.5 - 3.0 | 15-20 min |
If you see that the spray pattern is too dry and the material is rough, add 5-10% solvent. If the varnish begins to float and form smudges even with the correct distance of the gun (15-20 cm), it means that it is too liquid. In this case, the only thing that can save the situation is adding a small amount of pure varnish (without hardener) if the mixture has not yet begun to set.
What to do if the mixture begins to thicken in the tank?
If you feel that the varnish in the spray gun tank has begun to thicken (the shagreen has increased, the halyard has become narrower), stop painting immediately. Attempting to dilute the thickening mixture with a solvent will result in defects. It is necessary to pour out the contents, rinse the gun thoroughly and prepare a fresh portion. Using thickened varnish is guaranteed to ruin the appearance of the part.
The influence of temperature and humidity on breeding
The environment dictates its own rules of the game. The temperature of the air and the surface being painted is a critical parameter. At low temperatures (below +15°C), the processes of solvent evaporation and polymerization slow down. The varnish remains sticky for a long time, collecting dust, and may become cloudy due to condensation of moisture from the air. In such cases, “fast” hardeners and solvents are used.
In hot weather (above +25°C) the situation is the opposite: the solvent evaporates too quickly, preventing the varnish from spreading into a smooth surface. A rough shagreen is formed. What is needed here are “slow” solvents that allow the material to remain liquid longer. Also, in hot weather, you can slightly increase the proportion of solvent in the mixture, but not more than 10-15%, so as not to upset the balance of the dry residue.
Air humidity is the hidden enemy of the varnisher. At humidity levels above 80% there is a high likelihood of developing a defect known as "boiling" or whitish coating. Moisture condenses into the fresh layer of varnish and is sealed there. If you work in a garage without humidity control, try not to paint on rainy days or use special anti-silicon additives and moisture absorbers.
Use an infrared thermometer to measure the surface temperature of the part. Often the temperature of the body metal differs from the air temperature in the room, which can throw off your calculations for choosing a solvent.
Common mistakes and how to avoid them
One of the most common mistakes is “saving” on the hardener. Some craftsmen, wanting to save money or extend the life of the mixture, add less hardener than required. This results in the varnish taking weeks to dry, remaining soft, scratching easily and not holding polish. The chemical reaction cannot be fooled: the proportions must be precise.
Another mistake is using dirty containers. Residues of old varnish, base or solvent on the walls of the glass may react with the new material. Particularly dangerous are residues of nitro solvents or base enamels, which can cause swelling. Always use disposable cups or wash reusable ones thoroughly.
The error of improper mixing is also common. If you do not mix the varnish with the hardener well, there may be pure varnish in the lower layers of the spray gun, and hardener concentrate at the bottom of the glass. This will lead to uneven gloss and hardness of the coating in different areas of the part. Stir the mixture for at least 2-3 minutes, carefully moving the mixer along the bottom and walls.
⚠️ Attention: Never pour the remaining diluted varnish back into the same jar with the original product! This will lead to damage to the entire volume of varnish in the jar, since the curing reaction has already started. Dispose only into a separate waste container.
The key to the perfect varnish is not so much the skill of swinging a gun, but the precision of the mixture and the cleanliness of the work area. A mistake at the mixing stage is fatal and cannot be corrected by polishing.
FAQ: Frequently asked questions
Is it possible to thin thickened varnish with a solvent?
If the varnish has thickened due to the fact that a hardener has already been added to it and time has passed (a reaction has begun), then it is useless to dilute it. It will no longer fit correctly and will be defective. If the varnish has thickened in the jar (before mixing) due to long storage, you can try stirring and straining it, but it is better to test it on a test surface.
What is the difference between varnish hardener and paint hardener?
The chemical composition may be similar, but the proportions and reaction rates are often different. The varnish must be harder and more UV resistant, so varnish hardeners often have different characteristics. It is recommended to use components recommended by the manufacturer specifically for the varnish system.
How long does it take for the varnish to dry after painting?
The “dust off” time (when the dust no longer sticks) is 30-60 minutes at 20°C. Complete polymerization (hardening) takes from 7 to 24 hours. The varnish can be polished only after complete drying, usually after 24 hours, or after forced drying at 60°C for 30-40 minutes.
Why did the varnish become cloudy immediately after application?
Most likely, there was moisture in the mixture (high air humidity, wet compressor, cold part) or a low-quality, too fast solvent was used, which cooled the surface and caused moisture to condense from the air. Poor ventilation may also be the cause.