The quality of the car's finish directly depends on how well the paint and varnish material is prepared. Many craftsmen, especially beginners, often underestimate the importance of precise proportions when mixing two-component varnish with hardener and solvent. An error in dosage can lead to the coating blistering, not drying, or, conversely, losing its glossy shine before it has completely dried.
The process of preparing a working mixture is not just a mechanical connection of liquids, but the launch of a complex chemical polymerization reaction. Hardener starts the hardening process, making the coating durable, and solvent regulates viscosity, allowing the varnish to lie evenly on the surface of the body. Ignoring the manufacturer's instructions or using the wrong components often causes costly repainting.
In this article we will look in detail at how to dilute car polish to get the perfect “mirror” effect. You will learn about the influence of ambient temperature on the choice of components, understand the difference between fast and slow drying, and also learn to avoid common mistakes that even experienced painters make when working with HS and UHS systems.
System components: varnish, hardener and solvent
Modern car varnish is most often a two-component system, consisting of a base composition and a catalyst (hardener). The main substance is a transparent viscous mass, which itself takes a very long time to dry and does not have the necessary hardness. It is the addition of the hardener that triggers an irreversible chemical reaction, turning the liquid material into a durable polymer film that is scratch and UV resistant.
The third, no less important component is the diluent. His main task is to bring the mixture to the desired level. working viscosity. A varnish that is too thick will fall like shagreen and will not have time to spread, while an overly liquid varnish will flow down, forming unsightly sagging. It is important to understand that the thinner does not participate in the curing reaction, it only evaporates during the drying process, so its quality and evaporation rate are critical to the result.
When choosing components, you should pay attention to the compatibility of products from the same brand. Although many materials are universal, manufacturers often recommend using a “varnish + hardener + solvent” combination of one line to achieve a guaranteed result. The use of cheap hardener analogues can lead to clouding of the varnish or a decrease in its adhesion to the base paint.
⚠️ Attention: Never use acetone or 646 thinner to thin modern two-component varnishes. They can cause immediate coagulation (curling) of the material or clouding of the coating, which cannot be corrected by polishing.
Buy extra solvent. In hot weather, its consumption increases, since some of it evaporates from the spray gun before reaching the surface.
The chemical structure of hardeners also varies. There are standard, accelerated and slow options. The choice depends on the volume of work and the temperature conditions in the spray booth. For local repairs, standard kits are more often used, while for complete body painting in the cold season, special “winter” versions of components may be required.
The influence of temperature on the choice of solvent
The air temperature in the paint room is the main factor determining the choice of solvent speed. The physical processes of evaporation directly depend on heat: the hotter it is, the faster the material dries. If you use a “fast” solvent in hot weather, the varnish may dry out in the air without having time to spread over the surface, which will lead to an “orange peel” effect.
There are three main types of solvents based on evaporation rate:
- 🌡️ Fast: Designed to work at low temperatures (up to +20°C) or in rooms with powerful exhaust hood. It evaporates quickly, allowing for shorter drying times between coats.
- 🌡️ Normal: Universal option for temperature range from +20°C to +25°C. Provides a balance between spreadability and drying time.
- 🌡️ Slow: Necessary for hot weather (above +25°C) or when painting large areas. Gives the varnish more time to spread, preventing boiling.
Incorrect choice of solvent speed is one of the most common causes of defects. If you work in a cold chamber with a slow solvent, the varnish will take a long time to dry, increasing the risk of dust settling on the sticky surface. Conversely, a “fast” solvent in the heat can cause the next layer to lie on top of the already dried previous one, disrupting interlayer adhesion.
Experienced painters often mix solvents of different speeds to achieve the ideal conditions for a particular situation. For example, adding 10-15% "slow" solvent to "normal" will help improve flow on a cool day without dramatically increasing drying time. However, such experiments should be carried out only with materials from one manufacturer.
Exact proportions: mixing table
Maintaining proportions is a law, the violation of which leads to marriage. Varnish cans always indicate recommended ratios, usually expressed in parts by volume. The most common mixing ratios for two-component systems are 2:1 and 4:1, where the first number indicates the amount of varnish and the second the amount of hardener.
Below is a table of standard proportions for various types of varnishes. Please note that the amount of solvent may vary depending on the desired viscosity and the diameter of the spray gun nozzle, but the varnish-hardener ratio cannot be changed.
| System type | Proportion (Varnish: Hardener) | Adding solvent | Recommended nozzle |
|---|---|---|---|
| HS (High Solids) | 2 : 1 | 5-10% of the total mass | 1.3 - 1.4 mm |
| UHS (Ultra High Solids) | 4 : 1 | 0-5% (often not needed) | 1.2 - 1.3 mm |
| MS (Medium Solids) | 2 : 1 | 10-15% of the total mass | 1.4 - 1.5 mm |
| 1K (One-component, acrylic) | Not required | 10-20% (as needed) | 1.3 - 1.4 mm |
It is important to understand the difference between HS and MS varnishes. High solids (HS) materials contain less volatile matter, so they produce thicker layers per pass and are less susceptible to shrinkage. It is critical for them to maintain the exact proportion of hardener, since the slightest excess can make the mixture too thick to spray.
Never change the hardener proportion by eye. Increasing its amount will not speed up drying, but will make the coating brittle and prone to cracking.
To measure ingredients, it is best to use measuring cups with graduations that match your mixing system. Using kitchen scales is possible, but less convenient due to the different densities of liquids, which requires converting volumetric proportions into weight proportions.
Technology for preparing the working mixture
The mixing process requires care and cleanliness. Before starting work, make sure that all components are at room temperature (about 20°C). Cold varnish will be too viscous and difficult to mix evenly with the hardener, resulting in lumps or unmixed areas.
The sequence of actions should be as follows:
- Shake the can of base polish thoroughly, as heavy ingredients may have settled to the bottom.
- Measure the required amount of polish into a clean measuring container.
- Add a strictly measured amount of hardener.
- Pour in the solvent in the required proportion.
- Stir the mixture vigorously with a clean wooden or metal stirrer for 1-2 minutes, scraping down any material from the bottom and sides.
After mixing, the varnish should sit for 5-10 minutes (exposure time). This is necessary for the release of air bubbles formed during mixing and for the start of the primary chemical reaction. If you start painting right away, bubbles may appear on the surface, creating defects.
☑️ Check before painting
The pot life of the finished mixture is limited. For most two-component varnishes it is from 2 to 4 hours at 20°C. After this time, the material begins to thicken and loses its properties, becoming unsuitable for application. Do not try to dilute the thickened varnish with a solvent - the chemical reaction has already begun and the coating will be defective.
Checking viscosity and setting up the spray gun
Even if you follow the proportions indicated on the can, you may find that the varnish does not apply correctly. This is due to the fact that viscosity is not a constant parameter, but depends on the temperature and age of the material. For professional work, you must use a viscometer - a funnel with a calibrated hole.
The testing process is simple: fill the viscometer to the brim with varnish, start the stopwatch and time the time it takes for the stream to stop. The optimal flow time for most automotive clear coats is 14-18 seconds (for a DIN4 funnel). If the time is less, the varnish is too liquid; if it is more, you need to add a little solvent.
⚠️ Attention: When adding solvent to adjust viscosity, do not exceed the maximum threshold specified by the manufacturer (usually no more than 10-15%). Excess solvent reduces the solids and can lead to sagging of the varnish and loss of gloss.
The setting of the spray gun also plays a role. The pressure at the inlet to the gun is usually set in the range of 2.0-2.5 atmospheres, but the exact value depends on the model of the tool. Too high pressure will lead to strong fogging and waste of material, and low pressure will lead to poor atomization and shagreen.
What is a “dry” and “wet” layer?
The dry coat is applied from a greater distance and with less material to allow the solvent to evaporate. The wet coat is the final application where the varnish should flow into a glossy surface. For varnish, 1-2 wet coats are usually applied.
Typical errors and coating defects
Even experienced craftsmen are not immune to mistakes, but knowing the causes of defects helps to avoid them. The most common problem is boiling varnish (bubbles). It occurs when the solvent does not have time to evaporate from the lower layers and “breaks through” through the already set crust. Reason: too thick a layer, insufficient interlayer exposure or too “fast” solvent in the heat.
Another common defect is dullness or “whitening” of the varnish. This occurs when moisture enters the spray area. High air humidity or condensation in the compressor causes water to condense on the surface of the fresh varnish, making it cloudy. This can only be cured by complete repainting after thorough drying.
- 💧 Craters: Caused by silicone, oil or grease on the surface or in the air. The varnish “runs away” from dirt, forming round depressions.
- 🍊 Orange peel: A consequence of too thick varnish, high pressure or incorrect temperature. The surface does not have time to spread.
- 🌫️ Nebula: Appears when working in a cold room with a fast solvent. The surface cools due to evaporation, and moisture condenses on it.
To prevent these problems, preparation of not only the material, but also the work area is critical. The use of moisture separators, cleanliness of the compressor and absence of drafts are mandatory conditions. Remember that solvent is not just a liquid for dilution, it is a tool for controlling the behavior of the varnish on the surface.
⚠️ Attention: If you notice that the varnish has begun to thicken in the spray gun tank, stop working immediately. An attempt to dilute it and continue application is guaranteed to result in failure of the entire coating.
Frequently asked questions (FAQ)
Can varnish be thinned with gasoline or white spirit?
Absolutely not. Gasoline and white spirit have completely different chemical structures and are not intended to dissolve acrylic resins in car varnishes. Their use will lead to curling of the material, loss of adhesion and destruction of the coating in the shortest possible time.
How long does the polish take to dry after application?
Drying time “from dust” is about 30-60 minutes at 20°C. Complete polymerization (hardening) takes from 24 hours to several weeks. Drying in a chamber at 60°C speeds up the process to 30-40 minutes, allowing you to start polishing in a few hours.
What to do if the varnish bubbles immediately after application?
If bubbles appear immediately, the layer may be too thick or the solvent has not had time to evaporate. In some cases, carefully “nailing” the defect with an additional layer of varnish with a large amount of “slow” solvent helps, but often complete sanding and repainting is required.
Do I need to filter the varnish before pouring it into the spray gun?
Yes, definitely. Even new varnish may contain specks, clots or dust. Using a funnel filter (usually 125-190 microns) is a cheap way to avoid the costly polishing of the finished coating to remove inclusions.
Is it possible to mix varnishes from different manufacturers?
Theoretically, it is possible if they have the same chemical base (for example, both 2K acrylic), but manufacturers do not guarantee the result. The risk of incompatibility of hardeners is high, which can lead to cloudiness or lack of adhesion. It is better to use components of one system.