A General Guide for Effective Touch-up Work

Performing quality touch-up work can be difficult and in some cases impossible. The reason why effective touch-up work is so difficult to achieve is due to a discrepancy in porosity of the substrate and the existing coating. Any freshly damaged areas will absorb the touch-up coat at a different rate than the surrounding areas that had been previously painted; resulting in variances in color and gloss (also known as “Flashing”). Touch-up work showing flashing. Although touch-up work may not be possible in every situation, the list below provides a general set of conditions that typically must exist to effectively touch-up a surface. 5 Conditions for Effective Touch-up Work 1) The existing coating should have an MPI Gloss Level of either GL - 1 (a traditional flat finish) or GL - 2 (a traditional matte finish): Coatings with higher gloss levels will be too difficult to touch-up. Variances in light reflectance are significantly more noticeable with higher gloss paints. 2) The existing coating should be light: In general, deeper/darker colors are more difficult to touch-up effectively. Advertisement 3) The surface must not be exposed to critical lighting conditions: Even if the existing coating is an MPI GL - 1, touch-up work can appear visible under critical lighting conditions. 4) The same batch of paint must be used for touch-up: Different batches of paint will have slightly different qualities even though they are the same product from the same manufacturer. Even the slightest variance in color and sheen is noticeable when it appears side-by-side in the middle of a wall. In general, it is a good idea to keep a little bit of paint left over for touch-ups. 5) The same type of application tool must be used: Different application tools will provide different finishing textures, and will ultimately make any attempts at touch-up work visible. If the initial coating was applied by a roller, the touch-up work must be performed with a roller with the same nap size. Using a 10-mil nap roller to touch-up a surface that was applied with a 15-mil nap roller will create a significant variance in texture. Brush marks from touch-up work plainly visible on a rolled wall. If the surface in-question meets all 5 conditions listed above, there is a good chance that effective touch-up work will be possible. Keep in mind that while the list above does not guarantee whether or not a surface can be touched up successfully, it does provide a general set of conditions that are typically required for effective touch-up work. Whether a surface can be touched up at all depends on a range of factors including the finish’s gloss, color, method of initial application, and its location (especially where critical lighting is involved).   Sign Up to Get this Newsletter Forward Share Share Tweet +1 Advertisement

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Tips for Coating Galvanized Metal

Newly galvanized metal is a difficult substrate to coat because it is shiny and smooth with virtually no anchor pattern. Attempting to coat an un-dulled and excessively smooth galvanized surface will typically result in coatings failure, especially when these surfaces are not adequately primed. The story below highlights the consequences of using a high quality topcoat, without considering the role of priming and surface preparation. Chipping paint reveals neither primer nor surface preparation on underlying galvanized surfaces Galvanized steel parts were used in various places around the exterior of a shopping mall. To achieve the aesthetic vision of the project, these pieces were topcoated with a high performance latex to ensure long-lasting performance. After 5 years of service, some wear and tear (chalking, fading) of the topcoat can be expected, however the mall owner was not prepared to witness large pieces of paint peeling off and flaking down to bare metal. Convinced that the failure was not related to the high performance latex topcoat, an inspector was called in to determine the cause of failure. Inspection revealed that no primer had been used before the high performance latex topcoat was applied. Typically the primary role of a primer in an exterior metal coating system is corrosion resistance; however this is not the case for galvanized surfaces. The zinc galvanizing acts as a protective coating for the metal, so the main role of a primer in a galvanized metal coating system is to bond to the surface while promoting adhesion for the topcoat. lthough the lack of priming may have contributed to the coating failure, further analysis found that a lack of surface preparation was likely the primary cause. By examining the surface, the inspector found that the galvanized metal was still shiny and smooth, indicating that no preparation was used to roughen the surface. This failure could have been avoided if the newly-installed galvanized structures had been washed down with an etch primer (such as those listed under MPI# 25) to roughen and dull the surface, was allowed to dry for one day, and then primed with a waterbased acrylic primer (MPI# 134) before applying the high performance latex topcoat, allowing the topcoat to fulfill its expected service life.   Sign Up to Get this Newsletter Forward Share Share Tweet +1