CoatingsPro Magazine Supplements

STEEL 2019

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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COATINGSPRO STEEL SURFACES 2019 25 25 stripe coating or striping exists. No recognized standard provides direction concerning: • When striping/stripe coating should be specified; • Which generic paints/coatings/linings require stripe coating; • Whether a thickness should be specified for the stripe coat; • What application methods should be used for striping/ stripe coating. It's interesting to note that, to my knowledge, no paint manufacturer has conducted and formally published perfor- mance testing of its paint/coating/lining materials and systems using striping/stripe coating either. Further, the only information available concerning the success of striping/ stripe coating in prolonging paint system life is from field observations and anecdotal tales of paint/coating/lining existing structures. Out of those, we have gathered a few techniques that answer common questions in this area. • When should striping/stripe coating be specified? Striping/ stripe coatings should be specified when past history concerning the structure indicates that edge failure of the paint/coating/lining system has been a problem. Additional consideration should be given to specifying striping/ stripe coating if the environment is harsh or severe from a corrosion standpoint, and if the paint manufacturer recom- mends striping/stripe coating. e benefits of striping/stripe coating are two-fold. First, striping/stripe coating will tend to fill in small voids, laps, and irregularities in the substrate (such as porosity in welds). Second, striping/stripe coating, if allowed to cure to the point of tackiness, will tend to retard the next full coat of paint/coating/lining material from flowing away from edges. • Which generic paints warrant consideration of stripe coating? In general, low solids/low viscosity paints, such as alkyds, tend to benefit from striping/stripe coating. In general, fast setting coatings, such as inorganic zincs, and high-solid/high-viscosity coatings, such as epoxy mastics, may not derive benefit in film formation from striping. • Should a thickness be specified for the stripe coat? Striping/stripe coating is specified to be applied to edges and irregular surfaces, such as non-smooth welds, as a filler for surface irregularities and a recoatable surface for a subsequently applied full coat of the same paint/coating/ lining material to adhere to. Since the affected surfaces are usually irregular in shape or are edges, dry film thick- ness gages cannot be used to accurately determine paint/ coating/lining thickness in the stripe coated areas because currently available dry film gages do not work properly when placed too near an edge (typically <1 inch, or 25.4 microns). If the total dry film thickness limit for the paint/coating/lining utilized for striping/stripe coating is exceeded by applying both a stripe coat and a full coat, film defects, such as surface curing, solvent entrapment, and/or inter-coat delamination, may result. As such, the striping/stripe coat should be applied thinly. To achieve a competent stripe coat that is not excessively thick, the specifier of striping/stripe coating should require that the paint/coating/lining be applied only to produce a visual color change on the affected areas and not specify a numeric wet or dry film thickness. • What application methods should be used for striping/ stripe coating? Two methods for application of striping/ stripe coating seem to provide satisfactory results: Brushing; Spray application using conventional or air-assisted airless equipment combined with brushing after spraying. e specifier should permit one or both of these appli- cation methods for striping/stripe coating, depending on specific job conditions. For instance, brushing should be specified for the striping/stripe coating of small, complex shapes, such as lattice members and bolted connections, whereas spraying followed by brushing is appropriate for the edges of large structural shapes, such as wide-flange beams, stiffener plates, etc. Use of application methods that deposit relatively high volumes of paint material, such as rolling with a heav y nap roller or airless spraying, should not be E d g e f a i l u r e o n stiffener that was not striped/stripe coated. Premature coating failure on irregularly shaped weld that was not striped/stripe coated. Stripe Coating

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