The film doesn't look good? Maybe you didn't use the right thinner.

The general impression is that the thinner is only used to lower the viscosity of the material before application so that it can be easily applied. In fact, the role of the thinner does not stop there, its role in achieving a quality film is very important. The wrong thinner can ruin the look and feel of the film. The article below provides further information on the role of thinner and how to choose and use it.

Factors for choosing diluents

Thinners are not only used to obtain a low viscosity product. They can be used to control the drying and spreading of the film, so that the end result is a nice, drip-free appearance, orange peel or roughness. The choice of thinner also depends on the choice of gloss. The use of a varnish with a certain gloss does not guarantee that the varnish will achieve that gloss on the finished surface.

To avoid such problems, thinners with certain characteristics must be used. Choose them according to:

• ambient temperature,
• type of material to be thinned (primer or varnish),
• the desired gloss level,
• nature of the product (nitro, polyurethane, polyester)
• method of application used (spraying, pouring, waving).

For each of these cases, there are recommended thinners that work very well, but also contra-indicated thinners that can cause problems, sometimes serious ones. There are also universal thinners that can be used with any product. These are only for dilution, nothing more. In order to obtain a good quality end product, specific thinners must be used for each situation.

Summer and winter floods

Organic diluents are mixtures of solvents in different proportions. The solvents used have different properties that they transfer to the thinner. For example, if you need a thinner for summer, you would use heavy volatile solvents and for winter, light volatile solvents. Mixing is done with the purpose in mind.

Why is a heavy volatile thinner needed in summer and light volatile in winter? Because of the temperature dependency of finishing materials. If a fast thinner is used in summer, it will evaporate before the varnish sets very well on the wood, resulting in orange peel. If spraying, the lake can still dry from the air. The result is a fine powder which falls onto the wet varnish film and is absorbed into it (the film gasses), leaving a rough, rough film with many rough edges, unpleasant to the touch. For this reason it is advisable to use summer thinners, which are more volatile, or to add retarding thinners, i.e. thinners which delay evaporation.

In winter, the problem comes with drying. When the temperature is low, the film takes longer to dry and has time to trap impurities in the air. That's why specially formulated winter thinners that evaporate at lower temperatures are used to speed up drying. All these temperature-related drawbacks are eliminated if the temperature and humidity are kept constant whatever the season.

Influence of thinner on gloss

The influence of thinner is also seen in high-gloss varnishes and paints. To achieve that gloss you need a perfect surface that reflects light radiation as close as possible to 100%. It takes time for the film to set, and this time is provided by the thinner used. High gloss will never be achieved directly (i.e. without subsequent polishing) using a thinner that evaporates very quickly.

Different thinners are often recommended for primer and varnish. It is a way to cut costs. In general, faster thinners are cheaper. Use with primer is no bother, even if it results in a rough or orange-peel film. These can be corrected by sanding between layers. You can use a single thinner, the lacquer thinner (when they are of the same type - nitro, polyurethane, acrylic) for the whole system, in which case the costs will increase.

The choice of diluent also depends on the application method

The choice of a thinner also depends on the application method. For example, one of the important properties of the diluent is electrical conductivity. Conductivity depends on the polarity of the solvent, and for electrostatic field application you need polar solvents, which are good conductors of electricity.

In the case of pour-on application, the use of a rapidly volatile thinner leads to high thinner consumption and an alarming increase in VOC emissions. In waved application followed by UV curing, the thinner should be chosen so that it exits the film before entering under the lamps. If it does not evaporate by the time it gets under the lamps, it remains inside the film as an opalescence, which is totally unpleasant for transparent products.

My recommendation is not to treat the thinner as an unimportant auxiliary material. If you want to get good quality films, to have as few problems as possible during periods of extreme temperatures, choose the right thinner. If you can't manage, ask the finishing specialists for help. Above all, don't cut corners by buying cheap thinners. The price of a thinner is so low that the savings you make don't cover the risk of problems that can cost much more to fix.

I hope you find the information below useful. As always, additions are welcome. And if you have any questions or queries, please leave them below in the space provided. I will be sure to reply.