【Haichuan Anti-Corrosion Knowledge】Thinners: The “culprits” behind many paint film problems”

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Thinners: The “culprits” behind many paint film problems. I. The underestimated “supporting role” In anti-corrosion coating workshops, thinners are always the least noticeable components. People are more concerned about whether the paint is expensive, how useful it is, and its zinc powder content, but few pay attention to the thinners used in conjunction with the paint. Many people regard it as an optional “flavoring”—it doesn’t matter whether you add more or less, or what you add; as long as the gun nozzle doesn’t get clogged and the brush roller can still rotate. But veteran contractors know well: the materials determine the upper limit of protection, while the thinner determines how much of that potential can actually be realized. Many so-called “paint problems” are actually caused by the thinner doing its damage in secret. If you’re still not clear about what diluents do within the paint film, it’s recommended that you read this first: Why are diluents added to paint? What exactly is the diluent used to dilute? II. The root of problems often lies in the practice of using whatever solvent is available. The most fatal issues at the scene usually start at the moment when someone simply uses any solvent they can find. One of the most typical mistakes is adding incompatible solvents to two-component polyurethane paints (such as regular alcohol, alkyd thinners, or incompatible thinners). Alcoholic solvents can undergo side reactions with the isocyanate components, consuming the curing agent and interfering with normal cross-linking ； Other incompatible solvents may disrupt the dissolution equilibrium of the resin. The result is that the paint begins to heat up, thicken, or even gel while still in the bucket. Alternatively, after application, the paint film becomes powdery, brittle, and has very poor adhesion; it flakes off at the slightest touch, much like soybean dregs. This isn’t a problem with the paint itself; rather, the entire chemical system has been compromised from the outset. The reaction is incorrect; any further efforts will be in vain. III. The “tragic accidents between layers” caused by rushing the work: In anti-corrosion construction, there is one word to avoid at all costs – “rushing”. Before the primer has had a chance to settle, the topcoat is rushed on top of it. If a solvent with too high volatility is used for the topcoat, the solvents in the upper layer will act like strong acids, penetrating into the lower layers and softening or destroying the newly formed paint film structure. The consequences are the most common wrinkles and bulges. Upon tearing, the entire layer of paint peels off like orange peel, exposing the underlying surface – this is the typical case of \"paint eating through the substrate.\" Once it occurs, any partial repair is useless; it must be completely removed and rebuilt from scratch. III. The Invisible “Sponge Trap” There is another hidden killer, called “too much.” To facilitate construction, the diluent was added without restraint. The paint has become thinner, making spraying it easier, but you’ve planted countless \"bombs\" within the paint film. It may seem to dry quickly on the surface, but in reality a large amount of solvent gets trapped inside the paint film; eventually it has to force its way out of this film, leaving behind numerous tiny holes. To the naked eye, it appears smooth and even, but when scanned with an electric spark detector, the screen is filled with defects. The protective coating you spent a lot of money on turned out to be a leaky, riddled mess. The corrosive agents penetrate deep through these pinholes, reaching the actual steel surface, rendering the anti-corrosion coating completely useless. IV. Professionalism lies in rigor; ultimately, the key to diluents is not “how to add them,” but rather the rigor applied to the entire system. Truly experienced on-site managers usually focus solely on three things: compatibility – they use whatever the manufacturer provides, and never resort to mixing different components together. Limit: Strictly adhere to the recommended ratio (usually 5-20%, as specified by the manufacturer), and never exceed it based on intuition. Speed control: The evaporation rate can be adjusted flexibly according to temperature and humidity – slower when necessary, faster when appropriate. V. The outcome: it could have been controlled. Many people are used to checking the quality of the paint or changes in weather after an incident occurs, but they pay little attention to the issue of solvents. It’s like a ‘chronic bomb’ buried beneath the paint coat; in an effort to save some effort and speed up the process during construction, what is poured there isn’t liquid, but rather a huge bill that will have to be paid later when repairs are needed. It may deceive us in the short term, but it can never deceive time. Respecting diluents means respecting the quality of your own work! 、