For gel coat spray repairs, use a precision touch-up spray gun to spray the catalyzed gel coat mixture onto the damaged area. Spray 8 to 12 mils wet thickness. If you are spraying an area where the gel coat was completely removed, apply gel coat until achieving good hide (minimum 12 mils) using more than one pass.
For spot patching, use a knife or spatula to dab the catalyzed gel coat mixture into the damaged area. Slightly overfill the area, including the area around and above, to allow for shrinkage. Puncture and eliminate any air bubbles that may be trapped in the gel coat. Allow the patch to cure thoroughly. The patch is not cured sufficiently if a thumbnail leaves an impression in the gel coat.
Step 7: Finish the repaired area.
Initially sand with coarse grit sandpaper, followed by a succession of several finer grit sandpapers. The final sandpaper grit should make the patch flush to the part and remove scratches from the previous grit of sandpaper. Always use a clean shop rag to remove the sanding dust, oils, wax and other contaminates, especially when changing to a different sandpaper grit. Sand in one direction per grit size. For example, sand north/south with 400-grit and then east/west with 600-grit sandpaper.
Remove any remaining masking. Buff using a clean 100 percent wool pad with medium grit rubbing compound to smooth the surface. Wash the area with soap and water to remove the rubbing compound residue. Use a clean wool pad and a finishing glaze compound for the final buffing to remove swirl marks. Thoroughly wipe the area to remove all traces of the finishing glaze and residue. Wash the area with soap and water before waxing. Wax with a UV-stabilized exterior-protective paste wax.
By following these basic steps, you’ll be on the road to creating structurally sound, cosmetically appealing composites repairs.