High-quality car painting begins long before you pick up a spray gun, because 80% of the success of the entire process depends on the preparation of the material. Many beginners make the fatal mistake of believing that it is enough to simply open a can of paint and pour it into the spray tank, ignoring the physical and chemical properties auto enamels. In practice, paint that is too thick will form a shagreen (“orange peel”) appearance that is almost impossible to polish without damaging the coating, while paint that is too thin will instantly flow, leaving irreparable defects on the body.
The thinning process is not just mixing two liquids, but a precise engineering task that requires taking into account the temperature in the spray booth, the type of sprayer and the chemical composition of the enamel itself. Viscosity The material must be selected ideally so that the torch lies evenly, and the solvent has time to evaporate from the surface, forming a glossy film rather than matte spots. In this article we will look in detail at how to avoid common mistakes and achieve a result that will not differ from the factory one.
It is also worth considering that different types of paints, be it acrylic, varnish base or nitro enamel, require an individual approach and specific types of solvents. Using the wrong chemicals can cause the paint to curl up in the tank or, even worse, begin to peel after a few weeks of drying. Therefore, understanding the principles of mixing is a basic skill for any painter.
The choice of solvent and its effect on the result
The first step to successful painting is the correct choice of thinner, since it is this that determines the drying speed and spreading of the material. Solvents are divided into three main groups according to evaporation rate: fast, medium and slow, and the choice of a specific category directly depends on the air temperature in the room. If you use a fast solvent in a cold workshop, the paint may not have time to spread and will end up matte, and in the heat, a slow solvent will cause smudges to form.
The chemical composition of the solvent must strictly correspond to the type of paint and varnish material (paint and varnish material), otherwise incompatibility of the components may occur. For example, for acrylic enamels and varnishes, it is strictly forbidden to use aggressive solvents like 646 or 647 in their pure form without checking, as they can cause clouding or swelling of the coating. Always read the technical data sheet (TDS) on the paint can, where the manufacturer indicates the recommended types of thinners.
⚠️ Attention: Never use acetone or Galosh gasoline to dilute modern automotive enamels unless it is expressly stated in the instructions. These substances can disrupt the structure of the polymer, cause discoloration (fading) or lead to a complete loss of paint adhesion to the primer.
The temperature regime dictates its own rules: for work at +20°C and above, solvents with a normal evaporation rate are optimal, and for cold conditions (below +15°C) “fast” compositions are needed. However, working in cold weather is inherently risky, as condensation that forms on cold metal can get into the paint and cause defects. Therefore, professionals prefer to heat the room rather than experiment with solvent chemistry.
Necessary tools and workplace preparation
To mix the components well, you will need not only the paint and solvent itself, but also a number of specialized tools that ensure precision. The main device here is viscometer (most often a DIN4 funnel), which allows you to measure the time the liquid flows out and determine its readiness for use. Without this device, you will act “by eye,” which is unacceptable in professional painting and leads to defects.
We also have graduated measuring containers, usually transparent plastic cups with a percentage scale printed on them. The use of kitchen glasses or jars “by eye” is excluded, since even a 5% error in proportion can change the coverage and drying time. Also have wooden or plastic stirrers, funnels with strainers, and lint-free wipes ready to wipe down the edges of the container.
☑️ Checklist for preparing to mix paint
Safety when working with solvents comes first, as vapors of organic compounds are toxic and flammable. Be sure to use respirator with carbon filters, safety glasses and gloves, and provide strong ventilation in the work area. Static sparks or an open flame near an open can of solvent can ignite vapors, so avoid any sources of ignition.
Mixing proportions: table and standards
The mixing proportions of paint, hardener and solvent are always indicated on the manufacturer's label as a numerical ratio, for example, 2:1:10%. This means that for two parts of the base there is one part of the hardener and 10% of the solvent of the total mass of the mixture. Violation of these proportions leads to a change in the chemical properties of the coating: an excess of hardener will make the film brittle, and a lack of it will prevent it from completely polymerizing.
Below is a table with approximate proportions for various types of automotive paints, but the instructions on a specific can always take precedence:
| Enamel type | Base: Hardener | Adding solvent | Mixture life time |
|---|---|---|---|
| Acrylic 2K | 2: 1 (50%) | 5-10% of the mixture volume | 2-3 hours |
| Polyurethane varnish | 2: 1 (50%) | 5-15% depending on T° | 4-6 hours |
| Basecoat | Ready to use | 10-20% (solvent only) | 15-30 minutes |
| Soil filler | 4: 1 (25%) | 10-20% of the mixture volume | 1-2 hours |
It is important to understand the difference between adding solvent to the base and to the finished mixture. In some systems, the percentage of solvent is calculated from the volume of the base, in others - from the volume of the mass already mixed with the hardener. Technical map (TDS) always contains an exact algorithm: if it says “add 10%”, specify 10% of what exactly, so as not to make the paint too liquid.
What is paint pot life?
Pot life is the time during which paint mixed with a hardener retains its working properties. After this time has elapsed, irreversible chemical reactions begin in the mixture, the paint thickens, loses its shine and can curl into lumps right in the spray gun.>
Step-by-step instructions: how to thin paint
The mixing process requires consistency and precision. First, thoroughly mix the base in the jar, as pigments may have settled to the bottom during storage. Then pour the required amount of base into a measuring cup, using the scale for precise dosing, and only then add the hardener in strict accordance with the proportion.
After adding the hardener, the mixture must be mixed again, but without the solvent for now. Solvent is then added: the amount may vary depending on the desired viscosity and temperature. The final stage is to thoroughly mix all the components with a stick until a homogeneous mass is obtained without streaks on the walls of the glass.
After mixing, be sure to filter the paint through a funnel with a mesh strainer (usually 125-190 microns) directly into the spray tank. This will remove possible lumps, dust and skin particles that inevitably get into the mixture and can clog the sprayer nozzle. A clogged nozzle will result in paint spitting and streaks on the body, which will require repainting the element.
Adjusting viscosity using a viscometer
Determining viscosity “on the finger” or by dripping from a stick is for amateurs; professionals use a viscometer to obtain accurate data. A standard DIN4 funnel measures the time it takes 100 ml of liquid to flow through a calibrated orifice, and this time in seconds correlates with the viscosity in centipoise (cP).
For most automotive spray guns with a nozzle of 1.3-1.4 mm, the optimal viscosity of acrylic enamels is 16-18 seconds according to DIN4, and for primers - 20-25 seconds. If the flow time is less, the paint is too liquid and will flow; if it is longer, it will become shagreen. Adjust the viscosity by adding small amounts of solvent and measuring again.
⚠️ Attention: Measure viscosity at a mixture temperature of 20°C. If the paint is cold, its viscosity will be artificially high, and by adding a solvent “by instrument” in a cold state, you will get “water” after heating in the chamber.
The temperature of the paint itself will also affect the readings, so allow the mixed material to warm up to ambient temperature before measuring. Sudden changes in temperature can distort the results, so keep the components in the same room for at least 24 hours before starting work. The ideal temperature for measuring and painting is 20±2°C.
Typical errors and ways to resolve them
One of the most common mistakes is using old or contaminated solvent, which may contain water or dirt. Water that gets into the paint causes clouding (a whitish coating) and craters on the surface that cannot be removed by polishing. Always use only fresh, high-quality solvent in a tightly closed container.
Another mistake is insufficient mixing of the components, especially two-component systems. If the hardener is not distributed evenly, sticky spots or “eyes” will remain on the surface where the reaction has not proceeded to completion. You need to stir vigorously, scraping the composition from the bottom and walls of the glass, for at least 2-3 minutes.
Also, painters often ignore the “holding time” after mixing. Some materials need to be allowed to sit for 10-15 minutes before pouring into the spray gun to allow air bubbles to escape and the initial chemical reaction to complete. Pouring a “boiling” mixture will lead to porosity of the coating.
FAQ: Frequently asked questions
Is it possible to dilute thickened paint if it has been left mixed for a day?
No, if a hardener has already been added to the paint, then after 24 hours (and often faster) irreversible polymerization processes take place in it. Diluting such paint with a solvent will not restore its properties, but will only make the layer weak and sticky. The mixture with hardener must be disposed of after the pot life has expired.
What is the difference between base solvent and acrylic solvent?
The solvent for basecoat is usually more aggressive and evaporates quickly, since the base dries only due to the evaporation of the solvent and does not have a hardener. Acrylic thinner (2K) often contains evaporation retardants to give the material time to react chemically with the hardener and flow.
Why did the paint curl up in the can when mixed?
This occurs due to chemical incompatibility of the components. Most often this happens if you mix nitro paint with acrylic paint, or use an inappropriate, too aggressive solvent. The cause may also be water or silicone ingress. Curled paint cannot be saved.
What viscosity should I choose for a spray gun with a 1.6 mm nozzle?
For a 1.6 mm nozzle, which is usually used for primers or liquid putties, the viscosity should be higher - about 20-25 seconds according to DIN4. If you plan to pour paint through it, you will have to dilute it thinner, but this may reduce coverage, so it is better to change the dzu to 1.3-1.4 mm.