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How to Repair a Base Coat and a Clear Coat

Updated July 19, 2017

Most modern automotive paint refinishing systems use a water-based or solvent-based colour that is blended into vehicle panels. This is subsequently covered by a clear coat, usually made from urethane, which provides a resilient protective shell and a high level of gloss retention. A number of problems can arise during application but these can be dealt with quite easily as long as the defects are noticed at the right stage. Base colours can be rectified during the painting process while clear coats can be worked on once they are completely dry.

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  1. Leave the base colour to cure for 30 minutes if patching occurs and force dry with infrared lamps. Take an ultra-fine grade foam sanding pad and rub lightly over the applied base coat. Wipe off dust with a tack rag and adjust the fluid tip needle on the spray gun by twisting in a counter-clockwise direction to allow for additional material flow before re-coating

  2. Leave base coat materials to cure for up to 1 hour if runs and sags occur. Wrap a sheet of P1000-grit wet-and-dry paper around a rubber sanding block and lightly dampen it. Place the large, flat surface of the sanding block over the imperfection and move the arm in concentric circles to remove excess material. Dry the panel thoroughly with lint-free cloth and wipe over with a tack rag before applying a fresh coat of material.

  3. Soak a piece of lint-free cloth with slow-acting thinners and wipe the base coat from the panel to eliminate fisheyes. Fisheyes are caused by traces of silicon or grease on the surface of a panel. If imperfections appear in the first coat of base colour, rub down remnants with an ultra-fine grade foam sanding pad and tack clean. Wipe the surface of the panel thoroughly with degreaser and dry before reapplying the base colour.

  4. Remove traces of grit in clear coats by sanding off the heads with a damp piece of P2000-grit wet-and-dry paper. Take care not to rub through the clear coat otherwise the panel will have to be painted again. Once the grit has been sanded down to an even, flat surface, restore the shine by rubbing the affected area with cutting compound.

  5. Rub down runs in clear coat with a lightly abrasive piece of clay bar. Dampen the surface of the panel with water and rub the clay bar over the clear coat along the length of the run until the painted surface is completely flat. Again, the gloss of the material can be restored by rubbing with cutting compound.

  6. Dab oxidised areas with cutting compound and use an electrical polishing machine with a foam head to restore the gloss content. Oxidisation can occur when clear coats are exposed to excessive amounts of sunlight or moisture. On heavily-oxidised panels, rub down the entire painted surface with P2000-grit wet-and dry paper before polishing takes place.

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Things You'll Need

  • Ultra-fine grade foam sanding pad
  • Infrared lamps
  • Tack rag
  • Lint-free cloth
  • P1000-grit wet-and-dry paper
  • P2000-grit wet-and-dry paper
  • Water
  • Sanding block
  • Slow-acting thinners
  • Degreaser
  • Clay bar
  • Cutting compound
  • Electric polishing machine
  • Foam polishing head

About the Author

Based in the United Kingdom, Paul Miceli has been a professional writer since 2006. He has been published online by Ideate Media and Promiga and has a proven track record of producing informational articles and sales copy. Miceli is educated to U.K. "A-level" standard, continues to work as a paint sprayer and has more than 25 years of automotive body repair experience.

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