SOLVENTS AND THINNERS. WHAT’S THE DIFFERECE?
SOLVENTS AND THINNERS. WHAT'S THE DIFFERENCE?
The terms “solvent” and “thinner” are often confused, but in reality, they are different materials, and the mechanisms of their action are distinct. Let’s try to understand the difference and also explore which materials are better to use for thinning paint and why saving money on these materials can lead to negative consequences. First, let’s delve into the terminology.
Solvent is an organic volatile liquid (hydrocarbon, ketone, alcohol, ether, etc.) or a mixture of similar liquids that dissolve film-forming substances and provide the necessary consistency to paint materials.
Thinner is an organic volatile liquid used to dilute paint materials to reduce their viscosity and make them suitable for application to surfaces.
As we can see, the essence of solvents’ and thinners’ actions is directly reflected in their names.
Solvents are primarily liquids added to paint materials during manufacturing at the factory. Since the binding base of paint materials is usually either very viscous or solid, adding solvents allows giving them a convenient form for further work. Thanks to solvents, the paint (primer, lacquer) remains in a liquid state until applied to the surface and does not dry out.
It is easy to conclude that solvents can influence the structure of paint components, making them relatively aggressive liquids. Thinners, on the other hand, are less aggressive. Unlike solvents, they do not dissolve resins but only dilute the material to the required viscosity.
In most cases, the liquids we pour into primers, enamels, or paints before application do not have to dissolve anything. Their task is to adjust the viscosity.
ONLY “NATIVE”
The thing is, the same liquids can behave differently when combined with different paint materials: for some resins, they can act as thinners, while for others, they can be aggressive solvents. Therefore, the use of unregulated thinners can lead to incompatibility with the material and disastrous consequences.
Sometimes, indeed, such a property of “non-native” thinner can be useful: the macromolecules of the paint material change their shape, effectively reducing the material’s viscosity. Understandably, such thinners should not negatively affect the film-forming process, but most often, when there is a lack of “affinity,” this defect becomes evident.
The thing is, each thinner is specifically formulated for a particular material, considering its compatibility with the base and additives in its composition. The paint material developer, when incorporating specific liquids into the formulation, calculates the sequence and speed of chemical reactions, and thus, the correct choice of thinner determines the drying process and the final quality of the paint film (hardness, gloss, etc.). That’s why it is crucial to use only the recommended liquids for thinning paint materials.
However, such substitution is quite common: craftsmen choose high-quality and expensive primers, enamels, and paints but opt for the cheapest domestic thinners instead of the recommended ones, and then, after facing issues, cast doubt on the manufacturer of the paint material.
By no means do we want to say anything negative about domestic chemicals. Probably, these materials work well with certain types of industrial and household paints, for which they were originally developed. For instance, solvents from the 645-651 series were initially designed to work with nitro enamels, and this is clearly stated in the instructions for these products. However, they are not intended for thinning modern paint materials, especially imported ones.
BE CAREFUL!
Most traditional domestic solvents are highly reactive products. Take, for example, the well-known and widely used solvent 646 (from a physico-chemical point of view, it is indeed a solvent). It is a complex product that includes more than seven components (toluene, ethanol, butyl acetate, butanol, ethyl cellulose, acetone, etc.). This “explosive mixture” allows effectively dissolving many organic substances, making it highly popular on the market.
But what will happen if we add this solvent, let’s say, to an acrylic enamel or lacquer?
As we mentioned earlier, the paint material manufacturer selects specific thinners for their products with consideration of the rate and uniformity of evaporation. The components present in cheap solvents do not contribute to proper evaporation. Quite the opposite.
For instance, acetone, which is part of the 646 solvent, is too volatile and does not provide optimal drying of the paint film upon evaporation. It evaporates too quickly, leading to the immediate formation of a surface film, which hinders the escape of volatile substances from the depth of the layer. As a result, it causes familiar bubbling, reduced gloss, and decreased film hardness.
Excessive presence of alcohols in domestic solvents also has a detrimental effect on the film-forming process of acrylic paint materials. As we know, alcohols contain water, and water interferes with the proper polymerization of acrylic materials, redirecting the reaction in the wrong direction. In the end, instead of a strong polymer film, we get a “soft,” prone to settling coating with low gloss.
One should also be aware that the 646 solvent is aggressive towards many types of plastics!
Speaking about adding unregulated liquids to base enamels, it should be noted that it may cause the appearance of tone variations or stripes. Be prepared that these defects may only manifest themselves after varnishing and complete drying of the painted surface. There have been cases where defects appeared a few hours before handing over the car to the client. Not a pleasant experience, as they say.
Also, it is worth mentioning that the aggressive components in domestic solvents can “burn” certain particularly sensitive pigments in the enamel composition. This distorts the color of the paint, which is especially noticeable on light shades. For example, white enamel after adding solvent acquires a beige hue. While this color may have its merits, the car owner, for some reason, demands a pure white color…
IN CONCLUSION
Summing up, it becomes evident that budget liquids from dubious manufacturers cannot serve as full-fledged substitutes for branded thinners. This is also indicated by the manufacturing technology, where extremely cheap raw materials that have not undergone sufficient purification may be used. Hence, such liquids often result in a yellowish tint.
A high-quality thinner should be absolutely transparent and have no hues to avoid affecting the color of the enamel or paint!
Although such products cannot be used for their primary purpose, they can still be somewhat useful. For instance, they can be applied in solvent tests, for cleaning old soiled surfaces, or equipment flushing.