August 5 - August 11, 2013
How do you gauge the remaining service life of a weathered alkyd paint system and determine whether it should be removed or overcoated?
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jesse chasteen of schriener construction on
August 9, 2013:
Overall percentage of failure is one indicator. If the alkyd is weathered and aesthetics are not at issue, stay out of the wallet...times are tough.
Frank Rea of GPI-Southeast on
August 9, 2013:
The best way to determine if any coating system should be removed/replaced or overcoated is to perform a detailed condition assessment. Assuming the substrate is steel, first evaluate the type, amount, and location of corrosion using SSPC-Vis 2. Note other defects such as peeling, cracking, fading, etc., in the same manner. The spot repair and overcoat becomes less economical as the degree of coating failure increases. The next step is to take dry film thickness measurements, or, if destructive testing is not an issue, use a Tooke Gage so you will know not only the DFT but also the number of coats of paint. This information is important because you can only put so much paint on a surface before overcoating becomes risky. Collect a sample of the paint system and send it to a lab for heavy metal testing and infrared spectroscopy of the top coat. The presence of lead could affect your decisions on the maintenance scope of work. The infrared spectrograms will confirm the generic resin of the topcoat, so if you overcoat, you can choose a compatible coating. Observe the substrate to determine if the surface has been previously blasted or if mill scale is still present. Last, but not least, perform adhesion testing. The higher the adhesion rating, the less risk involved with overcoating. There are many other non-technical factors that must be considered, also. How long before the structure will be replaced? What is the cost of down time? Overcoating will get an asset back in operation more quickly. If it is a bridge, you need consider the inconvenience to the traveling public. What is your current budget? Removal/replacement may be the best option, but you may only have enough funds for overcoating. SSPC-PA 4, "Guide to Maintenance Repainting with Oil Base or Alkyd Paint Systems" is a good source of information. Good Luck, Frank.
john lienert of nehalem bay painting co. on
August 8, 2013:
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