Acrylic paints and varnishes have become a standard in body repair due to their environmental friendliness, drying speed and durability of the coating. However, even the highest quality auto enamel requires proper preparation before application, otherwise the ideal smoothness of the body will remain just a dream. Thick paint will not be able to spread properly, leaving shagreen, and too thin paint will flow, creating impenetrable “snot” on vertical surfaces.
The question is what solvent to dilute acrylic paint, is fundamental for the painter, because adhesion, gloss and absence of defects depend on the choice of chemistry. There is no universal remedy: what works perfectly with the base of one manufacturer can hopelessly ruin the material of another. In this article we will analyze in detail the chemistry of the processes, types of thinners and rules for their use to achieve factory-quality painting.
The first thing a beginner needs to understand is that acrylic paint consists of two components: the enamel itself and the hardener. The solvent is added as a third component solely to adjust the viscosity for specific operating conditions and the equipment used. Never use acetone or thinner 646 to thin a ready-mixed hardener unless the paint manufacturer specifically states their compatibility, as this may cause the compound to immediately curdle.
Process chemistry: why the right choice is important
Acrylic paints for cars are complex polymer systems. The process of their drying is not simply the evaporation of liquid, as with nitro enamels, but a chemical polymerization reaction triggered by the hardener. The solvent in this system plays the role of a temporary carrier, which must evaporate at a certain rate, allowing the paint molecules to line up in a strong network. If you choose too aggressive or, conversely, too slow chemistry, the structure of the layer will be damaged.
Evaporation rate is a key parameter. Fast solvent necessary in cold weather or when working in poorly heated chambers, so that the paint has time to “set” before dust settles on it. However, in hot weather, its use will lead to “boiling” (the appearance of microbubbles) and shagreen, since the top layer of crust is formed before the air has time to escape from the lower layers.
Slow formulations, on the contrary, give the paint more time to level, which provides a deep gloss. But their use in a cold room is fraught with drips and increased drying time, which increases the risk of insects or dust sticking to the sticky surface. The right balance allows acrylic varnish and the base to show its best decorative properties.
⚠️ Caution: Using an incompatible solvent may cause craters or orange peel defects that cannot be removed by polishing. Always check the Technical Data Sheet (TDS) before mixing.
In addition, it is important to consider the type of spray. Low pressure spray guns (HVLP) often require a less viscous mixture than high pressure systems. An error in the selection of solvent will lead to an incorrect spray pattern, and material transfer will deteriorate, which will lead to overuse of expensive auto enamel.
Types of solvents for automotive acrylics
There are many types of thinners on the automotive chemicals market, and they are all divided into several main categories depending on the chemical composition and evaporation rate. Understanding these differences will help you choose exactly what you need for your application. The main groups are universal, branded and specialized formulations.
Universal solvents such as 647 or 650, are often perceived as a panacea, but in professional body painting they should be treated with caution. They may contain aggressive alcohols or acetone, which can cloud the acrylic or change its shade. Their use is acceptable for washing equipment or priming, but for the final layer it is better to use specialized chemicals.
- 🧪 Brand thinners — designed specifically for a specific brand of paint (for example, Mobihel, Brulex, Vika), guarantee perfect compatibility of the components.
- ⏱️ Speed modifications — divided into fast (Fast), normal (Normal) and slow (Slow) depending on the ambient temperature.
- 💧 Water based — for water-soluble acrylics, special deionized mixtures are used; ordinary tap water is absolutely not suitable here because of the salts.
Two-component systems stand apart, where the solvent is part of the reaction equation. It is important not to confuse the concepts here: hardener and thinner are different things. The hardener starts the hardening reaction, and the solvent only regulates the viscosity. Mixing them in the wrong proportions or replacing one with another will lead to marriage.
When choosing, you should also pay attention to the purity of the product. Cheap analogues often contain impurities that can precipitate or cause yellowing in light colors. For premium mother-of-pearl and metallics, saving on solvent is unacceptable, since it determines how metal dust will lie in the base layer.
Compatibility table and mixing ratios
Compliance with proportions is a law, violation of which leads to financial losses. Manufacturers always indicate the recommended ratio of components on the can, and you can deviate from it only in exceptional cases, with a good understanding of the physics of the process. Below is a table showing typical ratios for different types of acrylic materials.
| Material type | Ratio (Base:Hardener) | Adding solvent | Solvent type |
|---|---|---|---|
| Acrylic enamel (2K) | 4:1 | 10-20% of the mixture volume | Specialized acrylic |
| Acrylic primer | 4:1 | 10-15% of the mixture volume | Universal or acrylic |
| Acrylic varnish | 2:1 | 5-10% (for the first layer) | Branded for varnishes |
| Base enamel | Does not require | 10-20% (depending on viscosity) | Special for bases |
It is important to understand that the percentage of solvent added is approximate. In reality, viscosity must be monitored visually and using a viscometer - a funnel that measures the flow time. The standard viscosity for applying acrylic is 16-18 seconds (using a DIN4 funnel). If the paint flows faster, it is too thin; if it flows slower, you need to add a little more thinner.
Always use graduated measuring cups when mixing. An eye in the painting business is the enemy of quality. First, the base is poured into the container, then the hardener is added, and only lastly the solvent is introduced until the desired consistency is achieved. All components must be mixed thoroughly to avoid separation.
☑️ Check before mixing
Temperature conditions and drying speed
Ambient temperature dictates the choice of solvent speed. This is an axiom of body repair. If the instructions for the solvent say “Normal”, this means working at an air temperature of about +20°C. Deviations from this value require correction.
In cold weather or in an unheated garage, using a normal or slow thinner will result in the paint simply not drying or, worse, dulling due to moisture condensing from the air on the cold surface. Here it is necessary fast solvent, which evaporates, heats the surface and accelerates polymerization. However, be careful: too rapid evaporation can “lock” the solvent inside the layer, causing the varnish to become cloudy.
In summer, when the temperature in the chamber exceeds +25°C, the normal solvent will evaporate faster than the paint will spread. The result will be large shagreen and dry spraying. In such conditions they switch to slow trains (Long, Slow), which extend the life of the exposed layer, allowing it to smooth out perfectly.
⚠️ Attention: Never try to speed up the drying of acrylic with a directed stream of hot air (hair dryer) immediately after application. This will lead to the formation of bubbles and an uneven coating structure.
Also remember about the temperature of the material itself. Paint brought from a cold warehouse should warm up to room temperature before mixing. Cold liquid has a different viscosity, and adding solvent “by eye” to a cold jar will lead to errors when heating the mixture during operation.
Application technology and working with a spray gun
Properly diluted paint is only half the success. The second half lies in setting up the spray gun. The gun inlet pressure, nozzle size and spray pattern must match the viscosity of the material. For acrylic enamels and varnishes, a nozzle size of 1.3-1.4 mm, for soils - 1.6-1.8 mm.
If after applying the first layer you see that the paint does not flow well and the surface looks rough, the mixture may be too thick. However, adding solvent to the already prepared mixture in the spray gun tank must be done with extreme caution. It is better to dilute a new portion of the correct consistency. An attempt to “save” thick paint by adding thinner on the fly often leads to a violation of the “base-hardener” proportion.
- 🔫 Pressure - usually 2.0-2.5 atm at the exit from the nozzle for acrylics.
- 🌬️ Torch - must be full and uniform, without breaks.
- 📏 Distance - keep the gun at a distance of 15-20 cm from the surface.
It is important to allow interlayer aging. Acrylic requires time for the solvent to evaporate before applying the next layer. If you apply a second coat too early, the solvent will “boil” under the new skin. If you overexpose it, the interlayer adhesion will be disrupted. Follow the manufacturer's recommendations on the can (usually 10-15 minutes at +20°C).
Frequent errors and coating defects
Even experienced craftsmen encounter defects, and most often their cause lies precisely in the incorrect use of the solvent. Understanding the nature of these defects helps to quickly diagnose the problem and fix it.
One of the most common defects is boiling. This is the appearance of small bubbles on the surface, which after drying turn into craters. Reason: solvent too fast, application of too thick a layer or insufficient drying between layers. The solvent does not have time to escape and breaks the surface.
Another scourge of painters - dullness (whitish coating). It occurs when the solvent evaporates too quickly, cooling the surface so much that moisture from the air condenses on it. This is a common problem when working in wet weather with fast solvents. This can only be corrected by sanding and reworking, adding a drying retardant to the new layer.
⚠️ Attention: Do not mix solvents from different manufacturers in one container. A chemical conflict between components can lead to an unpredictable reaction and damage to the entire batch of paint.
The “orange peel” (shagreen) defect is also encountered. If it is excessively large, the paint was too viscous (not enough solvent) or dried too quickly. Fine, factory-made shagreen is the norm, but it should be uniform. It can be eliminated by polishing, but it is better to prevent mistakes at the mixing stage.
FAQ: Frequently asked questions
Is it possible to dilute acrylic paint with regular gasoline or kerosene?
Absolutely not. Gasoline and kerosene have a completely different chemical structure, they are fatty and do not evaporate completely. Using them will result in the paint never drying completely, sticking and eventually peeling off.
Which solvent is better: 646, 647 or 650?
For acrylic automotive enamels, the most suitable of these three is considered 647 or 650 (acetone-containing), but only as a temporary solution or for soils. For finishing coats, it is better to use specialized solvents (P-12, Mobihel Standard, etc.), as they provide better fluidity and gloss without the risk of clouding.
How long does it take for diluted paint to dry?
The pot life of the finished mixture (base + hardener + solvent) is usually from 2 to 4 hours at a temperature of +20°C. After this time, gelation begins in the jar, and the material becomes unsuitable for application, although visually it may look normal.
Do I need to filter the paint after adding solvent?
Yes, definitely. Even if you use a new solvent, the mixing process or microscopic dust in the air can introduce particles into the mixture. Filtration through a funnel with a mesh (100-120 microns) before pouring into the spray gun is a mandatory step.
What to do if the paint thickens in the jar after an hour?
If an hour has passed into the paint with the hardener, it has already begun to polymerize. It is useless to add a solvent - the chemical reaction has already started. This mixture cannot be used, it will give a defect. It is necessary to dispose of the leftovers and prepare a new portion.