Introduction: Why the choice of solvent is important for paint quality
A solvent is not just a liquid for thinning paint, but a key component that affects final painting result, be it a car, a metal structure or walls in a house. Wrong choice can lead to curling paint, formation of lumps, uneven drying or even damage to the base. For example, aggressive acetone-based solvents can destroy plastic body parts, while too weak solvents will not be able to properly dissolve thickened enamel.
In this article we will look at how to choose a solvent for different types of paints (acrylic, alkyd, nitrocellulose, oil), consider their compatibility with materials (metal, plastic, wood) and give practical recommendations for dilution. We will pay special attention automotive enamels, where a mistake in choosing a solvent can cost expensive repainting.
You will also learn how to avoid common mistakes - for example, why you should not mix solvents of different brands or why Solvent No. 646 is absolutely not suitable for acrylic paints, despite its popularity. At the end of the article there is a FAQ with answers to frequently asked questions and a compatibility table for quick selection.
Types of solvents: classification and scope
All solvents are divided into organic and inorganic, but in car repair and construction, the former are mainly used. They, in turn, are classified according to their chemical composition and evaporation rate. Let's look at the main groups:
- 🔹 White spirit — universal solvent for oil paints and alkyd enamels. Suitable for cleaning instruments, but has a strong odor and evaporates slowly.
- 🔹 Acetone — aggressive solvent for nitro enamels and varnishes. Evaporates quickly, but can damage plastic and rubber.
- 🔹 Solvent 646 - a mixture of ethers, alcohols and acetone. Suitable for nitrocellulose and some acrylic paints, but requires caution.
- 🔹 R-12 — “soft” solvent for acrylic paints. Does not contain acetone, safe for plastic.
- 🔹 Xylene and toluene — used for diluting epoxy and polyurethane paints. Toxic, require respiratory protection.
It is important to understand that the same solvent can behave differently depending on temperature and humidity. For example, solvent 647 (analogous to 646, but with the addition of toluene) evaporates faster in the heat, which can lead to the formation of microcracks in fresh paint. Therefore, manufacturers often indicate on the can not only the type of solvent, but also recommended conditions of use.
Solvents for car paints: what to choose for body work
In auto repair, the choice of solvent depends on enamel type and painting method (air gun, airless spray, brush). Here, an error can result not only in paintwork defects, but also incompatibility of layers, if you are painting over an old coating. Let's look at the main options:
- 🚗 Acrylic enamels (for example, Mobihel, Sikkens): require solvents based on ethers and alcohols -
R-12,R-5or specialized, like Sikkens Thinner 2000. Acetone and 646 use it's impossible — they destroy the binder. - 🚗 Alkyd enamels (Duxone, Vika): compatible with white spirit, solvent or thinner
R-4. For quick drying you can add up to 10%646, but no more. - 🚗 Nitro enamels (less commonly used in cars, but found in restoration): diluted
646,647or acetone. Important! When working with nitro paints it is mandatory supply and exhaust ventilation - the vapors are toxic. - 🚗 Polyurethane and epoxy paints: require specialized solvents, e.g. PPG DT870 or Spies Hecker 5650. Self-dilution with white spirit or acetone will lead to coating peeling.
Pay special attention plastic parts (bumpers, moldings). Only solvents marked "For plastic" or "Plastic Safe", for example, APP Plastic Primer Thinner. Check compatibility in a small area!
Check the type of paint on the can (acrylic, alkyd, etc.)
Select a solvent from those recommended by the manufacturer
Filter the paint through a 100-150 micron mesh before thinning
Observe the proportions (usually 10-20% solvent by volume of paint)
Check the viscosity with a viscometer (for an air gun - 18-22 sec at 20°C)-->
Compatibility table for solvents and paints
To simplify the choice, we have compiled a compatibility table for the most common combinations. Please note: the data is valid for standard conditions (temperature 20-25°C, humidity up to 70%). In other conditions, adjustments may be necessary.
| Paint type | Recommended solvent | Acceptable analogues | What to Avoid |
|---|---|---|---|
| Acrylic (1K, 2K) | R-12, Sikkens Thinner 2000 | R-5, R-4 (in small quantities) | 646, acetone, white spirit |
| Alkyd enamel | White spirit, R-4 | Solvent, xylene (up to 10%) | Pure acetone |
| Nitroenamel | 646, 647 | Acetone (for quick drying) | White spirit, R-12 |
| Oil paint | White spirit, turpentine | Solvent (for thick paints) | Acetone, solvents for nitro enamels |
| Polyurethane | PPG DT870, Spies Hecker 5650 | Toluene (in small doses) | Universal solvents (646, 647) |
How to properly thin paint: proportions and technique
Even the right solvent can ruin the result if it is not dilution proportions. General rule: paint should have consistency liquid sour cream for brush or viscosity 18-22 sec (according to DIN 4 viscometer) for an air gun. However, the exact proportions depend on:
- 🎨 Application method: for a spray gun - 10-20% solvent, for a brush - up to 5-10%.
- 🌡️ Temperatures: in hot weather (>25°C) add 5-10% more solvent to slow drying.
- 💧 Humidity: at humidity >70% use solvents with evaporation retarders (for example, Sikkens Balancer).
Dilution technique:
- Pour the paint into a clean container (preferably glass or metal).
- Add solvent in small portions, constantly stirring with a wooden stick.
- Check the viscosity with a viscometer or visually: the paint should flow from the stick in an even stream, and not drip.
- Filter through the mesh
100-150 micronsbefore pouring into the spray gun.
If the paint begins to thicken while painting, do not add solvent directly to the spray gun tank - this will lead to uneven spraying. Instead, dilute a separate portion and add to the tank, after rinsing it.
Mistakes when choosing and using solvents
Even experienced painters sometimes make mistakes that spoil the result. Here are the most common:
- Mixing solvents of different brands. For example, adding
646in acrylic paint, dilutedR-12. This leads to coagulation and the formation of lumps. - Using expired solvent. Over time, solvents oxidize and lose their properties. Shelf life in a closed container: 12 months.
- Temperature not taken into account. In cold conditions (<15°C), the solvent evaporates too slowly, resulting in floats and long drying.
- Buying cheap analogues. Unknown brands of solvents may contain impurities that will discolor the paint or impair adhesion.
- Ignoring the manufacturer's instructions. The recommended solvent is always indicated on the paint can - do not neglect this information!
Another common mistake is storing thinned paint. If you haven't used all the paint, don't leave it thinned; the solvent will evaporate and the paint will thicken. It is best to store in the original container, tightly closed.
What to do if the paint has already curled?
If the paint has curdled after adding solvent, try straining it through a nylon stocking or a special paint filter (100 microns). If lumps remain, the paint will have to be disposed of - it will no longer be possible to restore its consistency. In the future, always test compatibility on a small amount of paint.
Solvent Safety: Protection and Disposal
Solvents are flammable and toxic substancesTherefore, compliance with safety precautions is mandatory. Here are the key rules:
- 🔥 Fire safety: Work away from open flames, sparks and heating devices. The flash point of most solvents is -
20-40°C. - 😷 Respiratory protection: Use a respirator with a filter
A1orA2(for organic vapors). An ordinary mask will not protect! - 👓 Skin and eye protection: Wear nitrile gloves and goggles. Contact of solvent on the skin causes irritation, and in the eyes - a chemical burn.
- 🌬️ Ventilation: Work in a well-ventilated area or use an exhaust hood. Solvent vapors are heavier than air and accumulate at the bottom.
Disposal:
- 🗑️ Residues of paint and solvent Do not pour into drains or onto the ground. Hand them over to hazardous waste collection point.
- ♻️ Solvent containers must be washed and dried before disposal. In some regions it is accepted as recyclable material.
For automotive work, the best choice is solvents marked “For auto enamels” or “Low VOC” (low content of volatile organic compounds). They are less toxic and meet environmental standards.
FAQ: Frequently asked questions about paint thinners
Can gasoline or kerosene be used instead of solvent?
No, this is highly not recommended. Gasoline and kerosene contain impurities that spoil the structure of the paint, and their evaporation takes too long. Exception - cleaning instruments from oil paints in the field, but even here it is better to use white spirit.
What solvent is best for painting plastic bumpers?
Only specialized solvents are suitable for plastic, e.g. APP Plastic Primer Thinner or Mobihel Plastic Additive. They do not contain aggressive components that could corrode plastic. Be sure to apply before painting primer for plastic.
What is the difference between solvent 646 and 647?
Both are universal solvents for nitro enamels, but 647 contains toluene, which accelerates drying and increases dissolving ability. However, 647 is more toxic and requires better ventilation. Both are not suitable for acrylic paints!
Is it possible to mix paints from different manufacturers if they are the same type?
Yes, but with caution. For example, acrylic paints Mobihel and Sikkens can be mixed if they are of the same group (1K or 2K). However the solvent must be compatible with both brands. Always test paint on a small area.
How to store solvents so that they do not lose their properties?
Store solvents in tightly closed original container at temperature 10-25°C, away from direct sunlight. Avoid storing in plastic bottles - some solvents (such as acetone) can dissolve plastic. Shelf life - up to 12 months.