Q. We have been experiencing craters or dimples in our current coating application process. We have spoken with our coating supplier, which said we may need to add an additive to eliminate this. What is this product, and how does it work? Have you used this, and would you recommend it?—A.F.
A. Contaminants are a reality with coatings. The defects you are experiencing can be introduced into your coating from your compressed air supply, cleaning solutions, silicones, greases, waxes, and even the oil in your hands.
This phenomenon you are noticing is referred to in the industry as “fish eye.” It can sometimes be a hair-pulling experience to try and isolate the source of contamination, as I have experienced in my career. One thing to note is that it is better to isolate the source and try to eliminate it as opposed to introducing any sort of “fish eye eliminator” into your coating and finishing operation.
Whether your coating is solvent- or water-based, the cratering effect is due to issues related to surface tension within the coatings from the contamination source. Most fish eye additives are a form of a silicone surfactant that when properly dosed and added to a coating will relax the surface tension of the coating, allowing the wet coat to level while is flashing off and drying. Typically, the recommended dose is very small, and is one additive that you do not want to use more than what is required as it can make this problem worse. Less is more. In extreme cases where I could not isolate my source of contaminate, I have used an additive to help eliminate fish eye.
However, once you start using an additive of this nature, you can introduce this silicone into your spray room environment, which usually does not end well, as the overspray can become airborne and find itself all over your shop and spray equipment.
Getting rid of these particles requires a very thorough cleaning of your entire spray room area including your spray equipment. I have had to do this many times and it can prove to be costly on all fronts.
One important note in regards to your compressed air supply is that a good set of coalescing filters for oil and water is a sound investment. Often, air supplies have automatic oilers to feed the lines, keeping certain sanding and grinding equipment from rusting while in use. Also, you may have noticed that on certain days, you can actually see water coming from your compressed air supply due to condensation built up during the compression cycles. Without the proper filtration, these oils and water can find their way into your paint coating through your spray equipment.
I realize that sometimes you have to do what you have to do to keep the finish room moving forward, but think first about good housekeeping and proper filtration, and use an additive as a very last resort.
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