Step 5: Measure and mix repair materials.
It’s critical to accurately measure all repair material quantities, including resins, gel coats, patch aids and peroxide initiators. These materials must be used within specified ratios to perform properly and allow completion of a successful and durable repair. The preferred measuring method is by weight. Low-cost scales can be purchased from local pharmacies, laboratory/hospital supply firms or scientific apparatus suppliers. The next best method is to measure by volume using graduated cylinders.
Many repairs are small and require small amounts of patching materials. Be sure to prepare materials in quantities that can be measured accurately even if the majority of the material is discarded. It is cheaper to discard excess material than to redo a repair because of inaccurate measurement.
For gel coat repairs, patch aids are recommended. Patch aids are resin- or monomer-based solutions that improve the working properties of gel coat when patching. They lower viscosity for easier spraying and reduced “orange peel” – or uneven surface texture. This reduces the time required to finish the repair. Patch aids also accelerate cure so that patches can be finished sooner and reduce surface tackiness for better sanding. Thinning gel coat with solvents such as acetone is not recommended. Solvents slow the cure of the gel coat and can result in off-color, dull and/or hazy patches.
Step 6: Apply repair materials.
For laminate repairs, use a roller or squeegee to pre-wet the glass. If working from the laminate backside, create the needed contour using cardboard or aluminum covered with cellophane prior to applying the glass to the repair area. If working from the front side, make a plug from cardboard with wires through the center, apply the glass to the plug and insert through the hole. Use the wire to secure the plug against the laminate until the resin cures. Remove air voids with a squeegee or roller. Allow the resin to cure thoroughly before proceeding.
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.
