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C O AT I N G S & L I N I N G S The Importance of Using the Manufacturer's Recommended Thinner FIguRE 2 • Poor blending of coating in overlapped areas • Orange peel appearance • Dry spray • Incomplete flm formation • Cratering • Inconsistent gloss Performance Properties • • • • • Solvent entrapment blisters. by the free volume within the flm, the environmental conditions, the thickness of the flm, and the ability of the solvent to migrate through to the coating surface. Solvents of a smaller molecular size, and with a straight chain structure, tend to release more readily from the flm than solvents that are of a larger molecule size, and/or are a branch chain solvent. Solvent System Design The solvent system design (both the solvent[s] used in the formulation and the recommended thinner[s]) must be formulated in a manner to ensure the drying and/or polymerizing functions within the flm properly occur prior to the loss of the majority of the solvents. As the solvents in the flm begin to evaporate, the blend of solvents that remain in the coating flm will change. If the frst and second stages of solvent loss do not occur correctly, many undesirable flm effects and performance issues may result. A solvent's primary function is to make the application of a coating practical or possible. As soon as the coating is dried, the solvent's primary function is complete. Generally speaking, solvent systems used for coating formulations are built from a mixture of solvent types. Each 46 MATERIALS PERFORMANCE May 2013 solvent type has a different intended function for that particular coating. Because of this, when considering a solvent to thin a coating, it is important to know which solvents work well together as well as which solvents work well with the various resin types. Using the wrong solvent to thin a coating can cause many different issues. An example of one such issue is that an improper solvent can potentially cause the resin to come out of the solution. This is commonly known as "solution kick out." Other examples of possible issues affecting application, aesthetic, and performance properties of a coating include: • • • • • • • • • Poor adhesion Pinholes/holidays Poor chemical resistance Blistering (Figure 2) Solvent attack of an underlying layer • Incomplete/retarded cure • Compromised time to moisture resistance Conclusions Through this brief overview on solvent types it should now be understood that there is no "universal solvent" that works effectively with every coating. Furthermore, there are many factors that have to be considered when choosing a solvent or blend of solvents to thin a coating. As has been discussed throughout this article, there are different types of solvents with various characteristics that can directly affect the performance and/or aesthetic appeal of a coating. Solvents used for thinning must be compatible with the constituents in the coating formulation, assist in creating Application Properties needed application properties, facilitate Poor sag resistance proper cure of the product, allow for the Poor fow and leveling desired aesthetic value, and help ensure Bubbling that the applied coating achieves the inFoaming tended level of performance. AdditionExcessive brush or roller drag Poor atomization such as "fngers" ally, issues revolving around compliance and public safety can be negatively imand "tails" Poor attraction to the substrate— pacted as well. Some of these issues include potential environmental regulations electrostatic application violations, NSF/ANSI 61 certifcation Aesthetic Properties violations, and AISC Slip Coeffcient and Runs and "curtains" (Figure 1) Creep Resistance for Critical ConnecBrush striations and roller marks tions certification violations. While a NACE International, Vol. 52, No. 5