When damage to the surface requires more than simple touch up paint application, repair of cracks can be performed using the following repair procedures.

Closely examine the problem area to determine if the cracked surface includes the fiberglass, or only goes as deep as the gel coat. If the answer is hard to determine using visual inspection, try rubbing the area using a fingernail. Cracks in the fiberglass will grab the fingernail; cracks in the gel coat will not grab the fingernail. In the event there is still doubt as to whether the crack is isolated to the gel coat surface, or goes beyond the gel coat down into the fiberglass, seek assistance through the trained eye of a body repair specialist.

If the crack is determined to exist in the fiberglass, it is then important to identify the cause of the damage. Damage to the fiberglass surface most often occurs from collision with another object, isolating repair to one particular instance. However, if the damage has appeared in a systematic pattern, with no explanation as to the cause, it may be necessary to re-enforce the area prior to undertaking fiberglass repair. If you suspect that fiberglass damage has occurred through reasons other than an object colliding with the vehicle, contact an authorized repair facility for assistance in determining the cause of fiberglass cracking, and the recommended service procedures to rectify the problem.

Clean the repair site and surrounding area using Acrysol, or a general-purpose adhesive cleanser. Repairs along the seams will require that you remove the vinyl trim, or peel the trim back far enough to perform the repair. Silicone seals along the vinyl trim will require removal from the repair site. Once the repair is complete, replace the seals.

Due to the grinding process required, a particle dust mask and safety glasses should be worn. Grind out the crack in the fiberglass using coarse sandpaper rated 36-grit. Grind the crack 1 to 2 inches in circumference of the damaged area. Taper down the depth to a paper-thin edge along the crack using 150-grit sandpaper to allow for bonding of the repair. Remove debris from the prepped area using a clean cloth and Diamont RM 900, available through most paint supply stores. Once thoroughly dry, mask off the repair site and cover the surrounding painted surface to protect against spills or over spray.

Cut sections of fiberglass matting material. Chop strand style matting is preferred in order to effectively build up layers. Generally, three layers of matting will be adequate to fill the prepared seam.

Wear disposable rubber gloves when working with chemicals. Mix a two part polyester resin and hardener inside a plastic tub. The mixing formula for hardener to resin will depend on the size of the repair. Refer to the manufacturer's packaging for the correct mixing ratio. Avoid adding excess hardener as this will only lead to problems that create additional work. Coat the seam using a disposable brush. The width of the brush will depend on the size of the repair site.

Dip layers, or attach the fiberglass matting at the repair site. It is important to saturate the matting with resin until the matting is transparent at the repair site. Use care to avoid over saturation. Use only enough resin to soak the fiberglass matting. Excess resin will not provide any additional strength to the repair. Finish by running a fiberglass roller over the matted resin to get the fiberglass matting to lay flat and eliminate air bubbles.

Time required to allow the repair site to cure will vary depending on environmental factors. Generally, 45 minutes to one hour is sufficient time for curing. However, if it is necessary to apply polyester body filler prior to sanding and painting in order to clear up small imperfections, 24 hours of cure time will be necessary for shrinkage and application of the polyester body filler.

Polyester body filler is used to fill sand and scratch marks and to seal the fiberglass repair site. Prior to adding body filler, the cured fiberglass repair site should be sanded flat. Start with 36-grit sandpaper on an orbital sander. Finish with 80-grit sandpaper, stopping when the repair site is at a slightly lower level than the existing finish. Body filler is a two-part product consisting of a base and a hardener. Mix according to packaging directions. Apply body filler using a 4-inch wide plastic applicator. Only a thin layer is required over the fiberglass repair. Curing time for the body filler is quicker than the fiberglass resin, generally 15 to 30 minutes.

Sand the cured area using a sanding block to ensure a smooth and even finish. Start with 80-grit sandpaper to knock down any high spots, followed by 150-180 grit sandpaper to smooth the area flat. Sand the area using light pressure, performing a systematic and even pattern over the repair site. Once done, wipe the entire area with a tack rag to remove dust and debris. Compressed air can also be applied to blow the area clear of dust particles.

To prepare the repair site for painting, prime the area using as catalyzed primer that will dry quickly with minimal shrinkage, such a Diamont DP 20. Paint codes are often included with the unit at the time of shipping. For more information on how to obtain a complete set of paint codes, contact National Parts at 1-877-466-6226.