The appearance of a “shagreen” surface, clogging of the nozzle or the formation of drips when painting a car is most often caused by a violation of the viscosity of the working solution. To avoid defects and rework, it is necessary to strictly observe the proportions of mixing the base composition with the solvent, since thick enamel does not spray properly, and too liquid flows off vertical surfaces.
The optimal viscosity for most spray guns is 20–26 seconds according to the VZ-246 viscometer, which corresponds to the consistency of whole milk. If you ignore this parameter and cast components “by eye,” you can ruin the expensive material and get paintwork defects that require a complete repainting of the element.
Modern paint and varnish materials such as acrylic enamels, two-component primers and metallics, require an individual approach to mixing. Using an unsuitable solvent or violating the temperature conditions leads to a change in the drying time and the quality of the torch spray.
The need for precise proportions
The quality of coloring directly depends on the physical and chemical properties of the finished mixture. Viscosity - this is a key parameter that determines how the material will behave when exiting the spray gun nozzle under compressed air pressure. Paint that is too thick creates a large flare, does not flow well, and leaves a rough finish known as “orange peel.”
On the other hand, an excess of solvent leads to a decrease in coverage and the appearance of streaks. This is especially critical for metallized coatings, where the violation of proportions changes the orientation of the aluminum powder, which visually changes the shade of the body. Therefore, the use of measuring cups or electronic scales is a mandatory requirement for professional work.
Each manufacturer of paints and varnishes indicates recommended ratios on the packaging, but they often require adjustment depending on the temperature in the paint booth. Summer and winter types of solvents have different evaporation rates, which affects the final result.
- 🔹 Compliance with proportions guarantees uniform spreading of the material over the surface.
- 🔹 Precise dosage prevents paint from drying inside the spray gun channels.
- 🔹 Correct viscosity ensures stable droplet size and high-quality torch.
- 🔹 The risk of matte appearance or loss of gloss after drying is reduced.
⚠️ Warning: Never rely on a visual assessment of the thickness of the paint in the can. The color and density of the pigment can give a false impression of viscosity, so checking with a viscometer is mandatory.
Main types of solvents and their compatibility
Choosing a thinner is no less important a step than calculating proportions. Solvents are divided into active and inert, and are also classified according to their evaporation rate. To work with spray gun Most often, active solvents are used that completely dissolve the film former.
The evaporation rate is selected depending on the ambient temperature. Fast solvents such as 646 or 647, are suitable for work in cold conditions, as they quickly evaporate, preventing the formation of smudges. Slow solvents, e.g. R-12 or special winter series, are necessary in hot weather so that the paint has time to spread before drying.
Incompatible components may result in paint curling, flakes, or loss of adhesion. It is important to use products of the same chemical group: nitro solvents for nitro enamels, esters for acrylics and special thinners for water bases.
⚠️ Attention: It is prohibited to mix solvents of different types (for example, solvent with acetone) in arbitrary proportions, as this can cause an unpredictable chemical reaction and damage to the material.
When working with two-component materials such as polyurethane varnishes and primers, Adding thinner before hardener may disrupt the polymerization process.
Table of mixing proportions for different materials
To obtain an ideal result, you need to know the exact ratio of components. Below are averaged data that serves as a basis for tuning. However, always check the specific manufacturer's technical documentation (TDS) as formulas may vary.
| Material type | Proportion (Base: Solvent) | Proportion (Base: Hardener) | Viscosity (sec) |
|---|---|---|---|
| Acrylic enamel (2K) | 10-15% of the mixture volume | 2:1 or 4:1 | 18-22 |
| Basic metallic | 1:1 or 1:0.8 | Not required | 16-18 |
| Soil filler | 5-10% of volume | 4:1 or 5:1 | 20-25 |
| Acrylic varnish | 5-10% of volume | 2:1 | 18-20 |
The percentage of solvent is often given as a range by the manufacturer. In this case, the choice of a specific value depends on the temperature in the chamber and the diameter of the spray gun nozzle. For smaller nozzles (1.3 mm) the mixture can be made a little thinner, for larger ones (1.7 mm) it can be thicker.
⚠️ Attention: Exceeding the amount of solvent by more than 15-20% of the recommended volume leads to a drop in the dry residual mass and a deterioration in the protective properties of the coating.
Preparing large volumes of mixture requires precision. If you are preparing 1 liter of paint, an error in 50 ml of solvent will significantly change the properties of the material, while for 100 ml the same error will be critical.
Step-by-step instructions for preparing the mixture
The mixing process requires a sequence of steps. First, the required amount of base (paint, primer or varnish) is measured into a clean container. Then a hardener is added (if the material is two-component) and thoroughly mixed until smooth.
Only after this is the solvent introduced. It is important to pour it gradually, constantly stirring the mixture. Sudden injection of a large volume of diluent may result in uneven distribution of the components. After adding the solvent, the mixture is thoroughly mixed again.
☑️ Paint preparation checklist
The finished mixture must be filtered through a special funnel filter to remove lumps and dust that could clog the spray gun nozzle. Using a filter is a must, even if the paint looks clean.
- 🔹 Open the can of paint and mix the contents thoroughly with a mixer.
- 🔹 Pour the required amount of base into a graduated glass.
- 🔹 Add hardener in strict proportion and mix.
- 🔹 Pour in the solvent, bringing the mixture to working viscosity.
The pot life of the finished mixture is limited. For materials with a hardener it ranges from 1 to 4 hours at a temperature of 20°C. After this time, the paint begins to thicken and loses its properties, becoming unsuitable for application.
Viscosity control and spray gun adjustment
Even if the proportions are maintained, the viscosity may vary. For precise adjustment, a viscometer is used - a funnel with a calibrated hole. The time of flow of the jet until the moment of the first rupture shows the viscosity in seconds.
If the flow time is longer than normal, the mixture is too thick and requires adding solvent. If it is less, the mixture is too liquid, which can lead to drips. For HVLP system spray guns Lower viscosity values are optimal than for high-pressure pneumatic tools.
How to use a viscometer
Close the funnel hole with your finger and pour paint to the brim. Remove your finger and start the stopwatch. Stop when the continuous stream stops and turns into dripping. The resulting time is the viscosity in seconds.
After achieving the desired viscosity, a test spray is performed on the test surface. This allows you to evaluate the shape of the torch and the quality of the spray. If necessary, adjust the pressure at the inlet to the spray gun or the position of the torch regulator.
It is critical to carry out all measuring and mixing at a component temperature of 20°C, since cold paint is always thicker, and hot paint is thinner, which distorts the readings.Common errors and ways to resolve them
One common mistake is adding solvent by eye. Experienced painters can determine the viscosity by the stream flowing from the mixer, but this method is not available to beginners and leads to defects. Always use measuring cups.
Another mistake is using dirty tools. Residues of old paint or solvent in the glass may react with the new material or simply contaminate the coating. Equipment must be thoroughly washed.
- 🔹 Ignoring exposure time (shutter speed) after mixing.
- 🔹 Using a solvent with the wrong evaporation rate.
- 🔹 Insufficient mixing of components leading to spotting.
- 🔹 An attempt to dilute ready-to-use paint (1K).
Tip: If you accidentally pour in too much solvent, do not try to evaporate it with heat. It's better to add a little more base (if volume allows) to restore balance, or use the mixture for less demanding jobs.
It is also worth mentioning the error of saving on filtering. Even a microscopic speck caught in the nozzle can change the geometry of the torch, which will lead to streaks on fresh varnish. Filtration is a cheap and quick way to avoid costly problems.
Safety precautions when working with chemicals
Working with solvents and paints requires strict safety precautions. Vapors from most solvents are toxic and flammable. The room must be equipped with effective ventilation.
The use of personal protective equipment (PPE) is mandatory. A respirator with carbon filters protects the lungs from organic solvents, and gloves prevent chemicals from coming into contact with the skin, which can cause dermatitis or allergies.
⚠️ Attention: Solvent vapors are heavier than air and can accumulate in the lower part of the room. Make sure that ventilation works not only at head level, but also below, near the floor.
The components should be stored in tightly closed containers, away from sources of fire and direct sunlight. Storage temperatures should generally not exceed 25-30°C to avoid pressure build-up inside the cans and changes in the properties of the materials.
Main conclusion: The quality of painting depends 80% on the correct preparation of the mixture. Accurate proportions, clean tools and viscosity control are more important than the brand of spray gun or compressor pressure.
Is it possible to use acetone instead of a special solvent?
It is not recommended to use pure acetone, as it has a very high evaporation rate and is aggressive. This can lead to instant drying of the paint in the nozzle (“boiling”) or clouding of the varnish. Use only recommended solvents.
What to do if the paint has dried in the spray gun tank?
Do not try to pick out dried paint with metal objects - you will damage the nozzle. Soak all removable parts in a special cleaning solvent or acetone for several hours, then blow with air.
Does air humidity affect proportions?
Humidity does not directly affect the proportions, but it does affect the drying process. At high humidity (>80%), a whitish coating (dullness) may appear on fresh varnish. In such cases, special anti-crater additives are used or drying is slowed down.
How long can thinned paint be stored?
One-component paints (nitro, some acrylics) can be stored in an airtight container for several months. Two-component mixtures (with a hardener) are viable from 1 to 24 hours, after which they polymerize and become unusable even in a closed jar.