Repainting Steam Locomotives

Article From: Products Finishing, ,

Posted on: 10/1/2002

Question:  I am the curator of a museum.

Question:

 I am the curator of a museum. We want to repaint a steam locomotive and tender. The steam locomotive was retired about 50 years ago. We have three issues to address. How can we get paints in the correct color? Which paints will preserve the units and provide long-term protection? How do we go about preparing for repainting the locomotive and tender? They will be spray painted. The units will be stored indoors. Volunteers will do the work. Can you help me to resolve these issues? M.A.

Answer:

To find a source for painting materials, I suggest you contact paint suppliers in the areas where the parent railroad has erection and repair shops. Fifty years ago, paint companies used the "200 mile" rule. They sold and shipped paint within a 200-mile radius of their plants. As for the specific colors, this information is available from the parent railroad or its successors and from railroad historical societies. It is also possible that the original paint supplier may have archived the paint color in question. It may be hard to believe, but all steam locomotives and tenders were not painted black. For example, the Pennsylvania Railroad painted theirs using Dark Green Locomotive Enamel, which only looked black.

Surface preparation, which includes cleaning and pretreatment, is the most important step in any painting operation. For coatings to adhere, surfaces to be repainted must be free from oily soils, corrosion products, loose particulates, as well as blistering and flaking paint. Oily soils must be removed by cleaning using solvents or aqueous chemicals. After cleaning, pretreatments are applied to enhance coating adhesion and, in the case of metals, corrosion resistance. Metals are generally pretreated using conversion coatings, such as phosphates, chromates, and oxides to passivate their surfaces and provide corrosion resistance. Abrading to remove rust and corrosion products by media blasting, sanding and brushing is also a pretreatment. In repainting operations it is often necessary to remove blistering and flaking paints. Mechanical removal of these surface defects is also a pretreatment.

Oily soils can be removed by applying aqueous chemicals using a steam spray cleaner, hot water spray cleaner or power washer. Detergent and alkaline cleaners applied using steam cleaners is a well-known degreasing method. The impingement of the steam and the action of the chemicals will dissolve and flush away heavy greases and waxes. Hot water spray cleaning using chemicals is nearly as effective as steam cleaning. Power spray washers are more modern pieces of equipment that rely on higher fluid pressures and the resultant greater impingement to remove soils. Oily soils must be removed before any other surface pretreatment is attempted. Otherwise these soils may be spread over the surface. They can also contaminate abrasive cleaning media, tools, and residues for disposal.

Loose and flaking rust and corrosion products must be removed by scraping or chipping prior to other pretreatments. Abrasive cleaning will remove adherent rust and corrosion products, and for this reason it is also considered a pretreatment, because the impingement of blasting media and the action of abrasive pads and brushes roughen the substrate and therefore enhance adhesion. Because of the possible fragile nature of locomotive and tender sheet metal, care must be taken to prevent warping and perforation of the sheet metal.

Blistered and flaking paint must be removed to prevent failure of the newly applied finish system. They are best removed manually using a putty knife or chipping tool.

Spot priming of bare metal must be done within an hour of abrading to protect it from corrosion. Bare metal that has been pretreated with a conversion coating must also be spot primed. A shop primer, such as a modified medium oil alkyd, that is compatible with the existing paints on the locomotive and tender and with available topcoats is recommended. The shop primer should be applied to all bare spots at a dry film thickness (DFT) of 2 mils (0.002 inch).

The prime coat, using the aforementioned shop primer, must be applied to all surfaces of the locomotive and tender to be repainted before application of any topcoats. This will ensure compatibility of the subsequent topcoats with the existing finish system. The primer should be applied to the entire locomotive and tender at a DFT of 2 mils (0.002 in).

Cosmetic repair of locomotive and tender surfaces to remove dings and dents can be done after spot priming and before full priming using automotive quality body putty, if necessary.

The topcoat of a finish system is not only decorative, it also provides overall environmental protection to the painted surface. It is recommended that a two-component polyurethane be applied to fully primed locomotive and tender to be repainted. It should be applied at a DFT of 1.5-2 mils.

 

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