A Little More You Should Know About Paint SOLVENT POPPING You’re not a painter, but do you know what “solvent popping” is? Solvent popping occurs when trapped solvent in the paint expands arid breaks through the applied paint film. Inside each solvent kernel is moisture, add heat and the water expands and blows it apart. The solvent is like spheres, you can actually see them embedded if you go down through a dried paint film, especially a clear coat. They reach different levels in the paint film, and you cannot buff them out. If you sand them, then you are left with the problem of pin holing. Bottom-line, the paint has to be removed and re-sprayed. What types of things occur with solvent popping? Here are just a couple: Blistering: This describes bumps in dried paint film that looks like small pimples or bubbles. This can be caused by moisture trapped in the paint film, insufficient drying time after wet-sanding, contamination in the air lines used by the painter or even heavy humidity during paint application. Air Entrapment: This is relatively rare in painting and can be caused by trapped air pockets in the wet paint film. Having the spray gun too close or moving the gun too slowly while not having sufficient air pressure can cause this problem. It usually can be rubbed out. Dust Contamination: This is not as much a problem today because of the implementation of dust-free paint booths. The chief cause of the problems today include the use of poor grade masking paper, particles coming from inexpensive degrading air lines, poor vehicle prep and a painter with dirty work clothes. Dust particles usually will rub out. To best understand the concept of solvent popping what I want to do is ask and answer a few questions about solvent popping that were presented and answered by a number of automotive coatings experts. • What is happening when solvent popping occurs? Simply, solvent in the paint is coming out. Solvent is the medium used to spray the paint. And, the solvent has to completely evaporate for the paint to cure or crosslink. This does not happen when the solvent “pops.” What happens is the top layer of the paint crosslinks with solvent underneath. Later, when the solvent tries to evaporate, that is to go from a liquid state to a gas, you have a solvent pop. It is just like popcorn where there is moisture inside of each kernel. Add heat and the water expands inside the kernel and blows it apart. Paint does the same thing, blowing the paint apart. • What is the gas you speak of? Air? No, it is solvent changing from a liquid to a gaseous state. • Is the gas flammable? Yes, but they would be better called combustible on a DOT scale. • So for the painter and/or the detailer this is a bad problem? Yes, without question because there is not a quick fix. Bottom line, if solvent popping has occurred on a paint finish it has to be removed and repainted. • What actually causes solvent popping? It can be a combination of things in the painting process. The spray gun, the painter and what is called film buildtoo much paint. • So even if you have a paint booth, good spray gun and an experienced painter, if too much paint is applied you can have a problem? There also is the <strong>issue</strong> of the solvent chosen. If the painter chooses too fast a solvent you are going to have problems. The biggest problem is the painter’s unwillingness to change, to do things the old way. You have atmospheric changes depending on the season and you must adjust the solvents. In the fall things dry too slowly and in the spring is when you see solvent popping occur. • I have heard that shop owners tell their painters “don’t buy anymore solvent until you use up what we have got in inventory.” Is that a problem? As mentioned, there is a variety of solvents in every paint product. That means there will be a variety of evaporation rates in the solvents used to manufacture the paint. If the painter uses a fast reducer that does not mean that all the solvent in the paint would be “fast evaporating.” There also could be some slow evaporating solvent as well. As the temperature increases, if you continue to add fast solvent the top of the paint will form a film or skin over which traps the slow evaporating solvent, and eventually you will get solvent popping as this solvent tries to get out. • Are paint companies trying to develop products to reach the correct flow to avoid painter error? Yes! If the paint has to do things to adjust for poor chemistry then there is trouble. Paint companies need to put out “idiot-proof ” paint, so to speak. • Until those products come along what can the painter do to prevent problems? The paint shops and detailers should purchase the “solvent package” that is designed for the paint. For example, when we talk about a clear-coat we mean ready-to-spray. Everything is there, paint, reducer, etc. We have designed a package and have tested it in a variety of situations. We know it works, if you use all the parts. Unfortunately, some shop owners, in an effort to save money, will buy cheap paint and cheap solvents. Some will buy good paint and cheap solvents. • You hear painters complain about the quality of the paint. For example, “the car was perfect last night but when I came in this morning the hood, roof and deck were all bubbled over.” What is this all about? This was a problem with air dry lacquer primers and sealers, but we don’t use these any longer. It can still occur, however, where there is super high humidity, like in the Southeast Coastal area in the late summer. What happens here is the painter uses slow solvents because it is hot, but with the humidity so high the solvents are even slower and won’t come out. Then you have heat speeding up the cross linking reaction. 24 | AUTO DETAILING NEWS | VOL. 5, NO. 4 • WINTER 2020
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