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Ask the Expert Question-and-Answer Archive by Ron Joseph January, 2005 Paint for Mailboxes Q. I have started a home based business for handpainted mailboxes. I use water based acrylic paints on standard metal rural mailboxes. I have already used a metal primer to help the paint stick but I would like to know what kind of (store bought) protective sealing I can put over the artwork when finished that will be strong, weather resistant, won't allow peeling and will not effect the color of the paints? A. The best approach would be to apply a clear acrylic based coating if you have the ability to spray the coating on would be my first choice. You should investigate your options by visiting your local paint supplier. Tell them about your project, and ask for specific product and application recommendations. You may find a clear waterbased acrylic product, but be certain to explain that these items will be exposed to exterior conditions. If you are unsuccessful here, then investigate automotive quality products. Here again these products are designed to be spray applied. You may find some solvent based acrylic lacquers, or something equivalent. The ultimate in exterior durability would be a two-component polyurethane clear coating, but this is really intended for professionals who have spray equipment, spray booths and appropriate personal protective clothing, including respirators. I would strongly advise you to avoid using this type of coating unless you are equipped to spray-apply it safely. Would you consider taking a handful of your hand-painted mailboxes to a custom paint shop in your area and ask them to apply the clearcoat for you? I would imagine that the finished product will look awesome! Finally, you would need to conduct some basic tests to confirm that the polyurethane does not lift the previously applied coatings. First, you would need to allow the coatings that you have applied to dry and cure for at least a week before you apply the solvent-based clear coat. After applying the clear cat wait another week before performing an adhesion test. Using an Xacto knife or blade cut, or scribe several parallel lines horizontally and vertically into the coatings so that you form a grid of squares, approximately 1 mm per side. The lines must penetrate all the way through to the substrate. Now apply a piece of aluminum duct tape to the grid. Press it down firmly and wait for about 90 seconds. Pull the tape back upon itself quite quickly, almost ripping it off the coating. Look to see if the coatings are adhering to each other, or if they come off with the tape. If they do not come off, you should be in good shape. If they do come off, then either lengthen the intercoating times or write to me again telling me exactly what you found. When preparing any surface for the application of paints or coatings, be certain to take precautions to protect against breathing in any air borne dust particles or debris that may be created by the prep work. Please be aware that paints, coatings and solvents are chemicals and therefore you should always pay attention to proper handling procedures and be prepared to wear protective clothing, such as respirators, gloves, coveralls, etc. For further information on the health and safety requirements for the coatings and solvents you wish to use we strongly advised you to contact your local coating supplier. If possible, go the extra step and look for this information on the website of the product vendor. Regards, Jim Burke |