Hull Repair – Scratches

01/20/2013: Faired small scratches above the water line before painting with Awlgrip. Also used 80 grit to grind out a palm sized delaminated area below the water line, sealing with epoxy, then 2 layers of bottom paint without fairing smooth.

  1. Notes:
    1. Siren’s hull is made up of the following materials ordered from inside to outside:
    2. Fiberglass
    3. Blue gel-coat
    4. White gel-coat
    5. Paint
      1. Primer/Awlgrip paint (above the waterline)
      2. Trinidad red covered with West PCA Gold
  2. Prepare surface for repair.
    1. Clean the area with Acetone and clean rags. Acetone is harsh on the liver, so wear rubber gloves.
    2. Use a grinder (or 80-200 grit sandpaper for smaller cuts) to fair the edges of the scratch.
      1. There should be no overhanging material or sharp edges.
      2. A V-shape cut is ideal, but a cupped shape works almost just as well. Just don’t deepen the cut to achieve the V-shape!
      3. I used a screwdriver to create the V on one long scratch at the aft end, port side through the Siren decal.
    3. If the scratch went through the gelcoat into the fiberglass, some fiberglass repair may be required as well. (See Fiberglass Repair.)
    4. Wipe the area with Acetone and clean rags.
    5. Tape off the surrounding area with masking tape.
  3. Fill the scratch with resin and micro-balloons or micro-fiber. (Q-cell is too weak, micro-fiber is hard to sand but stronger. Use micro-fiber when strength is required.)
    1. Note: gelcoat paste and polyester putties may distort and yellow with time. Polyester resin doesn’t stick or flex as well. Epoxy fillers are the way to go.
    2. Follow the instructions on the container for proper mixing. Too much hardener and the epoxy will react too quickly. Too little and it will never harden making it impossible to sand. If you mix too much at once, it will react more quickly and feed itself heat until it’s a boiling, smoking volcano of hardening goo. If you need to apply a lot at once, spread it out in a larger container.
    3. Mix thoroughly with mixing stick or chopsticks so each molecule of epoxy touches a molecule of hardener.
    4. Mix in the micro-balloons until it is a peanut butter consistency. Too thick it won’t apply smoothly and will pull itself out as you slide the squeegee over the repair. Too thin and it will droop out of a cut in a vertical surface.
    5. Don’t apply too much at once. If it’s a deep cut, apply a layer, let it dry to a tacky feel, then add another layer. Use a squeegee cut to size to smooth the last layer.
    6. Continue adding layers until the paste is built up equal to or just higher than the surrounding surface.
  4. Sand the repair area.
    1. Use the lightest grit sandpaper you can get away with. If 320 takes forever, step down to 220 or 120 or even 80 if you botched something and have a ton of material to grind away. With courser grits it’s easier to make a bad mistake and damage the surrounding surface. If you are painting over the repair, finish the sanding with 220 grit. Use a random orbital sander or sanding block. Don’t sand with your fingers or it will result in a wavy appearance.
    2. Inspect the surrounding area often, and once the sandpaper just begins to touch the original surface, stop sanding.
  5. Inspect and sand, or add another layer.
    1. If the area is still too wavy or too shallow, add another layer of filler.
    2. If the area looks fair and clean continue.
  6. Add a barrier coat.
    1. Water likes to soak into the cavities of micro-balloon filler so we need to cover the repair with a barrier coat like InterProtect 2000E first.
    2. A layer of epoxy brushed on with no filler works as a barrier coat as well (for small areas).
  7. Paint over the repair to match the previously applied paint.
    1. How do we match the new paint with the old faded paint?
  8. Polish to match the boat if the paint supports it.
    1. Awlgrip paint contains clear coat that floats to the surface as it dries. This layer is fairly thin, so do NOT polish Awlgrip paint or you will remove the clear coat. Wax shouldn’t be used either. It will look great for a couple weeks, then dull quickly.
    2. Polishing works very well with gelcoat.
    3. During this buffing stage, stop and dry the area often to check your progress.
    4. Wet-sand with 800 grit sandpaper to remove the scratches from previous sandings.
    5. Then step up to 1200 grit sandpaper.
    6. Continue stepping up to finer sandpaper to as high as 1500 grit to 2000 grit until you match the shine of the entire boat.
    7. If you want more shine than that, polish the entire hull (See Cleaning Hull).
  9. Wax if the paint supports it.
    1. Don’t wax Awlgrip paint.
    2. Gelcoat likes wax, which can be added as a protective layer.

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