2. Remove any surface contaminants such as wax, oil or mold release. Wipe an area at least twice as large as the damaged area with a wax and silicone remover (Dupont Prep-Sol® #3919S), acetone or other appropriate solvent. Dry the area with clean paper towels before the solvent evaporates.

Figure 2-2 Open shallow and minor cracks with a V-shaped scraper such as a sharpened can opener.	Figure 2-3 Grind out an area of many closely spaced or deep cracks with a disk grinder.

a. Shallow cracks or scrapes that affect only the gelcoat layer may be repaired with the gelcoat repair technique described in Section 2.2.1. If necessary, reinforce the laminate to reduce flexing as described in Section 2.3. Some small cracks or chips can be filled with a gelcoat touchup kit.

b. Minor cracks or scrapes that run through the gelcoat into the first chopped strand mat layers of the laminate  should be repaired with epoxy using the procedures described below (Section 2.1). Finish with the gelcoat repair technique described later in Section 2.2.1. If necessary, reinforce the laminate to reduce flexing as described in Section 3.

c. Deep cracks extending into woven fabric of the laminate require a structural repair before beginning the cosmetic gelcoat repair. If the crack extends into or through the woven fabric of the skin, follow the procedures in Section 4. If a core has delaminated or is damaged from moisture penetration or impact, follow the appropriate procedure in Section 5.

2.1 Minor crack and abrasion repair

Minor cracks and scrapes that extend to the chopped strand mat layers of laminate may be repaired with WEST SYSTEM epoxy.

Scraped out damage

If cracks were exposed with a “V” shaped scraper, complete the repair as follows after preparing the damaged area as described above:

1. Feather the edges with the scraper or with 100-grit sandpaper and brush the surface free of dust and loose material.

2. Wet out the cracks with a resin/hardener mixture.

3. Fill the cracks with a thickened epoxy mixture using the flat end of a mixing stick or a plastic spreader. Thicken the resin/hardener mixture to the consistency of peanut butter with 404 or 406 filler. Trowel the mixture flush with the surface and remove excess epoxy before it begins to cure. Allow the epoxy to cure thoroughly.

4. Sand the area smooth. Use 100-grit paper to remove any bumps or ridges. Finish by wet-sanding with 220-grit.

5. Finish the area with gelcoat or paint following the procedure in Section 2.2. Reinforce the laminate as necessary to reduce flexing, following the procedure in Section 3.

Ground out damage

If the damage is the result of a scrape or gouge, or cracks were exposed with a grinder, complete the repair as follows:

1. Grind a shallow, 20-to-1 slope around the damaged area. Remove any dust or loose material.

2. Wet out the repair area with a resin/hardener mixture.

3. Fill the void with an epoxy/404 or 406 mixture, thickened to the consistency of peanut butter. Use a plastic spreader to shape the mixture to match the surface contour. Leave the mixture slightly higher than the surrounding area and remove any excess before it begins to cure. Allow the epoxy to cure thoroughly.

4. Sand the area to blend with the surrounding contour. Use 50-grit paper to remove any bumps or ridges and finish with 80-grit paper when you are close to the final shape.

5. Fill any remaining voids (if necessary), repeating Steps 3 and 4.

6. Apply two or three very thin coats of epoxy to seal the surface. Extend each coat slightly beyond the previous one to feather the edge. The area may be warmed with a heat lamp to speed the cure and to help the epoxy flow out. Allow the final coat to cure thoroughly.

7. Wet sand the area with 180-grit paper to prepare for the final finish.

8. Finish the area with paint or the gelcoat finishing procedure beginning with step 4. Reinforce the laminate as necessary to reduce flexing, following the procedure in Section 3.

2.2 Finishing

Although many types of coating systems are compatible with WEST SYSTEM epoxy and provide the necessary UV protection, we recommend polyester gelcoat for small repair areas and linear polyurethane paint for large repairs. Although gelcoat may be used over large areas, it lends itself better to small areas where it’s necessary to color match existing gelcoat and its handling characteristics are more manageable. Linear polyurethane paints give extremely durable finishes and are appropriate for large complete sections like a hull or deck where color matching is not critical. Paint application over a large area is more practical than gelcoat. These finishes are recommended for above the waterline only. Use WEST SYSTEM for all repairs and coating below the waterline, prior to applying bottom paint.

2.2.1 Gelcoat finishes

In answer to questions concerning compatibility and techniques for applying polyester gelcoats over repairs made with WEST SYSTEM® epoxy, we can say epoxy provides an excellent base for polyester gelcoats. The following procedure will assure good adhesion and a well matched repair color. If you have only a shallow crack or scrape that does not extend into the laminate, begin with Step 1. If you have repaired minor cracks or scrapes with epoxy and are ready to proceed with the final gelcoat finish, begin with Step 4. Be sure the epoxy has cured thoroughly. Wash the surface thoroughly to remove all traces of amine blush.

1. Remove any surface contaminants such as wax, oil or mold release. Wipe an area at least twice as large as the damaged area with a wax and silicone remover (Dupont Prep-Sol™ #3919S), acetone or appropriate solvent. Dry the area with clean paper towels before the solvent evaporates.

2. Scrape out the cracks or scratches with a 90° “V” shaped scraper to expose clean gelcoat and increase the bonding area slightly. Do not scrape through the gelcoat.

3. Fill the scraped out voids with gelcoat. Mix a small batch of gelcoat without thinners. Trowel the mixture into the voids, leaving it slightly higher than the surface. Allow the gelcoat mixture to cure thoroughly.

4. Apply tape around the perimeter of the de-waxed area. Mask the area beyond the repair to protect the boat from overspray. If there is a molded bodyline or corner near the repair, you may want to extend the color patch to that point. The same is true for a painted or vinyl stripe.

5. Sand the additional area out to the tape line with 320-grit paper. This will be the total area to be gelcoated.

6. Determine the gelcoat batch size for the size of the repair–approximately 80 square feet per gallon of gelcoat (20 sq ft per qt).

7. Tint the batch of gelcoat to match the color of the boat. If the boat is fairly new and the manufacturer is still in business, you may be able to get gelcoat that will be a very close color match. If this is not an option, you will need to get the gelcoat from a FRP product supplier. Many marine distributors handle the gelcoats from various resin manufacturers. You will also need pigments to tint the base color to obtain a good match. These pigments are generally available from the gelcoat suppliers. Frequently, local repair yards that do fiberglass repairs will sell these products.

There are gelcoat additives (available through most gelcoat suppliers) that, when used properly, make matching a repair easier. These are clear, low-viscosity resins that are not air inhibited. These products are mixed with the pigmented gelcoat in place of a wax solution to provide a tack-free cured surface. They also provide the added benefit of thinning the gelcoat without changing the color of the cured patch the way acetone or styrene can. Gelcoat additives are manufactured by Duratec, and Cook Paint and Varnish Company.

Matching the repair color to the color of the boat can be difficult. Most gelcoat colors change as they cure. As you tint the gelcoat to match, apply a small amount of uncatalyzed material to the sanded area surrounding the repair. Use your gloved finger to spread this into a sample the size of a quarter. Wait a couple of minutes for the solvents to flash off. Any color variation will be evident. If the color match is not acceptable, change the color by adding small amounts of tinting pigments. As you adjust the gelcoat color, think in terms of the basic color hues, i.e.; the color needs to be more red, blue, green or yellow. This will help you identify which of the pigments to use. Use very small amounts of the pigments. When the hue is right, adjust the brightness, darker or lighter by adding black or white. It will take much more white pigment to lighten a mixture than it will a small amount of black pigment to darken it. Apply an uncatalyzed smear with each change of color no matter how small. Leave each of these smears on the surface until you have the color as close to the boat color as you can get it. When you are satisfied with the color match, wipe away all of the test smears with acetone or lacquer thinner.

8. Divide the batch into a 2/3 portion and a 1/3 portion. Our technique for using the patching additives is slightly different than the recommended procedure.

9. Mix the patching additive with equal parts of the 2/3 portion of the matched gelcoat. Catalyze following the recommendations of the gelcoat supplier. Over or under catalyzation may prevent the product from reaching a proper cure.

Apply this mixed gelcoat to the repair with a spray gun. Apply several light coats, feathering each one farther from the repair area. Allow the solvent to flash off between coats. You may need to apply five or six coats to hide the shadow of the repair. Most gelcoats will cure lighter in color if they are too thin. Most manufacturers recommend a total film thickness of 15 to 20 mils. Avoid applying the gelcoat in two or three heavy coats, which may cause solvent entrapment and improper curing. This may also have an effect on the color of the cured repair.

10. Mix a second batch using the 1/3 portion of gelcoat and patching additive. This time use about three parts of patching additive with one part gelcoat.

Spray the first coat of this mixture over the previously sprayed area. Then apply two or three more coats of this mixture over the entire area. Extend each coat farther than the previous one, with the last coat out to the tape line. The semitransparent film of lightly tinted clear patching additive will allow the original gelcoat color to show through around the perimeter of the patch. This will help blend any subtle color change into the original gelcoat.

11. Allow the gelcoat to reach a full cure. Pull the tape and sand the tape line smooth. Start with 320-grit wet or dry paper and work up to 600-grit. Sand the surface of the repair if necessary.

12. Buff the surface with a white, medium-cut rubbing compound. Take your time and do not overheat the surface while buffing. The excess heat can cause a stain that will be very difficult to remove. Finish with a fine compound and wax the area.

There are times when the repair will not match simply because the original gelcoat color has faded. You may need to polish the entire section of the boat to restore the original color.

2.2.2 Paint finishes

Although almost any high-quality marine-grade paint will work, we recommend using one of the two-part polyurethane paint systems above the waterline. (Below the waterline, apply

bottom paint directly over thoroughly cured WEST SYSTEM epoxy.) These paints provide ultraviolet protection, have good gloss retention and a durable, abrasion-resistant surface, provided you follow the manufacturer’s instructions carefully. Light colors, especially white, are recommended over dark colors. White reflects UV and infrared radiation better than other colors and all other things being equal outlasts other colors. Polyurethanes adhere well to fiberglass surfaces bonded with both polyester and epoxy resins. Note: seal all areas of sanded 407 and 410 Microlight fairing compound with epoxy before applying primers or paints.

It is possible to color match small areas, particularly if they are in fairly inconspicuous locations. However, if you have a large repair, or several smaller repairs over a large area, you may find it easier to repaint the entire hull or deck.

Polyurethanes, just like epoxies, are affected by moisture contamination. This means use caution when painting: don’t paint early in the morning or late in the afternoon. Also avoid painting in direct sunlight.

If you’ve chosen to paint, you will probably be painting the entire hull, deck or cabin top. Begin by inspecting the entire surface. Wipe with a silicone and wax remover (such as DuPont Prep-Sol™#3919-S) to eliminate any trace of mold release agents or wax. It may require two or three washings. Thoroughly abrade the surface to be painted by wet-sanding with 180-grit sandpaper, followed by 220-grit. Follow the paint manufacturer’s recommendation for the final grit. Generally, the thinner the paint, the finer the grit of the final sanding. You must remove all glossiness from the surface. Polyurethanes tend to highlight any surface imperfections, rather than hide them. Check for nicks, dings or gouges and repair them as described previously.

After all repairs have been made, wash the entire painting surface with the paint manufacturer’s recommended solvent. Follow the manufacturer’s mixing and application instructions to the letter. It’s far better to apply two or three thin coats than one thick coat.

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