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Before attempting any type of coating, be sure that surfaces to receive treatment are scrupulously cleaned and prepared. Oil, dust, oxidation, mold parting coatings, paint, lacquer , lettering, moisture and some cements can inhibit proper bonding. Body oils can produce beautiful finger prints in paint finishes. Cleaning may be as simple as washing dishes with detergent wash, rinse and dry cycles. More stubborn cases may require brushing with an old tooth brush to remove sticky contaminants and depression trapped, air bubbles which may block contact. Plastics frequently have a silicone parting solution residue, which is not easily removed with colder, comfortable detergent solutions. Poly S Plastic Prep can remove these at room temperature. Removing all paint is relatively easy, requiring a suitable container (jar), a good solvent that does not attack model's material and some patience. A common practice on unpainted brass rollingstock has been to apply lacquer to hide blemishes or solder and prevent oxidation during handling. Although usually very thin, this may not be a good paint base, since, especially on older models, oxidation often occurs at a later date in spite of coating. The best all around, inexpensive solvent found to date is a fairly strong mixture of ammonia (ammonium hydroxide) and lye (sodium hydroxide). It has proven safe on styrene, but not on skin, and produces some etching on brass and zamac. On short contact, unprotected fingers will appear very smooth and slippery. Longer exposure will darken skin, which may peel off later. Long term immersion of very old zamac may produce surface deterioration. As process continues, solution grows very cloudy from dissolved or flaked paint, requiring occasional progress peeks using tongs. An occasional scrubbing with an old tooth brush can help remove large flakes or paint in corners to speed up the process. Agitation by stirring, shaking or vibrating accelerates process. Placing container in a SONIC CLEANER _is faster. After use and a prolonged period, suspended particles will precipitate, and liquid may be decanted to a new container, permitting sediment to be discarded from old. Solution may be refreshed by adding ingredients . Some paints (Floquil and baked Scalecoat) are very difficult to remove. Many chemicals have been suggested over the years, including brake fluid, but success was marginal. Restricted by possible damage suits, commercial products fare no better. One, fairly expensive product with a fancy reptilian name, was not worth the price of the container. Agitation will speed process, especially decavitation developed in a sonic cleaner. Wood and byproducts are not very amenable to immersion, which often raises grain and fuzz or disintegrates fiber structures. Abrasive or scraping methods fare much better. Sanding and other dust may be removed with a brush, tack cloth or vacuum cleaner. Without a sealing coat, some woods soak up lighter vehicle paints like a sponge. Wood that will represent metal or smooth surfaces requires sealing with several coats of a good filler, such as Scalcoat Sanding Sealer. When thoroughly dry, between each coat, light abrasion with very fine steel wool will remove raised fuzz. An almost glassy finish may be attained, which when painted, simulates sheet metal very well. Although highly discouraged for modelrailroad use, due to instability, weakness and porosity, balsa requires a special, heavily filled sealer. Oxides present poor or loose bonding surfaces and therefore must be removed. Often if not removed or permitted to develop after painting, flaking occurs. The bulk of rust and similar oxides may be removed by a wire brush, followed by an acid bath. Weaker acids like vinegar (acetic acid) can remove oxides on brass, zamac or steel, given sufficient time. Strong acids are not recommended, since they can be very dangerous and the process is difficult to control. Ie. small parts and details may dissolve. An alternative method is to use FAST CUTTING ABRASIVE AIR-BLASTING . to remove finishes, oxides or excess solder and also to etch surfaces to improve bond. Another, often used industrially and by jewelers, is a lapidary tumbler with a revolving drum. Using abrasives from peanut shells to sharp carbides, they can polish as well. Many hobbyshops carry them in various sizes. Often lettering must be removed to some extent for application of a new coating or alteration. Since almost all lettering is raised to some extent, it will show through thin coatings, because curved surfaces or outline edges will reflect light at angles of incidence different from a level base coat overlaying it. Removal is usually by the same methods used for base coats, but may require more time for solvent to react or scrubbing with a brush. Particularly with heat stamped, the lettering surface may be harder and more impervious than the undercoat. A little judicious scraping with a dental pick or sanding may be necessary to break through the shell to permit faster chemical softening or dissolving. To represent a paint-out job on an old car, some traces of lettering may be retained. To alter lettering some portions must be removed; hopefully, without damaging the undercoat. Once decals are sealed with an overspray, removal is practically impossible without damage. Although much thicker, most heat stamped, stenciled and silkscreened lettering can be successfully removed, damage free, with extreme care. Since the lettering surface may be harder and more impervious than the undercoat, a little judicious scraping with a dental pick or sanding may be required to break through the shell to permit chemical softening or dissolving for removal. With a fine brush, a series of very light applications is made, restricted to the raised lettering only, if possible. After a short wait, very light, careful rubbing with a small cotton swab will pick up softened medium, avoiding contact with base coat. Even though it is not always easy, Poly S Easy-Lift-Off has been the most successful. Slowly and carefully, the procedure is repeated. Occasionally a little extra scraping helps in stubborn areas. The touchiest part occurs near the later stages as lettering thins. Usually it is better to set the project aside to permit the base coat to harden, before final removal. Otherwise a softened coat may absorb some of the the lettering color. If all rubbing strokes are downward, a very nice bleeding effect, ala the prototype, may result. With some practice , individual characters may be removed for number changes. If the right font and size can be found, dry transfers are much easier to use. Often they are more intense than original lettering and decals, but variation, including font and size, often exists in the prototype in later years. As an alternative method, an air-eraser with a light cutting abrasive can easily remove lettering without damage. Some materials require special treatments, prior to coating. Smooth, shiny metal surfaces lack enough tooth for coatings to bond well. Primer coatings, like Floquil's zinc chromate, work well; but add thickness to layer and require over a week to set. If applied too soon, a beautiful pink tint may bleed through succeeding coat. Beware, some primers are colors rather than bonders. In most cases weak chemical or abrasive blast, etching is preferable. Particularly during shipping, styrene acquires and later exhibits a poor property. Large and rapid temperature changes create, often imperceptible, internal stresses in the structure , which later become quite evident when additional surface stress occurs, during painting with some solvents. Causing great surface stress, Floquil's Dio-Sol thinner, contains xylene; which is often used industrially to weld styrene. Application to internally stressed styrene can produce disastrous effects by allowing the stresses to rise to the weakened surface. This often appears as crazing, cracks or a spider web effect. One solution is to anneal the structure by immersion in an, approximately 160 ° F, water bath for about an hour to be safe. Floquil's Barrier can be used, but it increases coat thickness and care must be taken that shield is complete. After any chemical processing, items must be rinsed thoroughly with a neutralizer or copious amounts of water; as reaction may continue, even on what appears to be a dry, clean surface. Finally, after cleaning, plastic gloves should be worn to keep, oil laden, cotton pickin' fingers off the prepped surfaces. Prior to starting, media, equipment and area should be prepared. Medium should be thinned properly and thoroughly mixed to evenly distribute pigments, vehicle and any required additives. Particularly for spraying, straining may be necessary. Brushes must be squeaky clean to induce even paint flow down bristles. Airbrush nozzle parts must be clean, with no residue. A very thin coating of petroleum jelly may be applied to help eliminate sticking paint. All traces of dust should be removed. Particularly with carpeted floors, foot movement stirs up dust, which may be seen in a ray of light. To eliminate this and protect floor, a plastic runner should cover area. BACK TO PAINTING AND COATING BACK TO METHODS INDEX |
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