Repair & cleaning

Common repair problems

Please refer to the “Resin Sealing” section.

Fiber blooming is when vein-like glass fibers break through to the surface of a composite part. It’s caused by surface trauma like drilling, cutting, hole punching, UV exposure or sanding.

To repair, please refer to the “Resin sealing” section.

Please refer to the “Splicing” section

Please refer to the “Resin Filling” section.

Please refer to the “Glass lay-up” section.

Please refer to the “Hole filling” section.


We recommend routine cleaning as part of your composites’ preventative maintenance. If you plan to make a repair, you should clean the area using the methods described in this section.

To remove any foreign material that may interfere with repair or cause electrical problems, it is necessary to clean your composite product with either solvents or a steam cleaner.

Note: If your surface is due to be adhesively bonded, do not use this method.

Contaminated surfaces can be thoroughly cleaned by wiping with a clean, non-abrasive cloth dampened with a solvent such as acetone, toluol, or methyl alcohol. The cloth will require repeated soaking as the solvent liquid evaporates easily.

Once the surface is clear of debris, wipe dry with a clean cloth.

Do not immerse or soak the composite in solvent

Do not use spray solvents

If required, an abrasive cloth can be used for tougher cleaning. However, this may result in surface damage requiring repair before the composite is fit for service.

  1. Steam heat should not exceed 120° C / 250°F and pressure must remain below 5.8 bar / 85 psi
  2. If possible, elevate one end of the composite product. This enables the dirt and condensed water to drain.
  3. Do apply steam jet directly to adhesive joints as this may loosen them.
  4. If you are going to repair a cleaned composite surface, leave the composite for a full 24 hours after cleaning to ensure it is completely dry.
  5. Use solvent to remove difficult substances, such as tar.

Minor impact from bolts, tools or other items striking the composite’s surface will usually have minimal effect on its performance or mechanical properties. However, there may be cosmetic issues which require attention. An Exel representative will be happy to help.

Resin sealing

  • Sand the damaged area and clean as required. If you use solvent cleaner, let the composite dry thoroughly
  • Ensure the area is free of dust and completely dry before proceeding
  • Take your selected sealant and carefully apply it to the damaged surface. Ensure you follow manufacturer guidelines on ventilation and fume safety
  • Carefully remove any excess sealant with a cloth and leave the composite to cure
  • Do not sand the area as this will reopen the seal

We recommend catalyzed resins to seal our composites as resins tend to provide better corrosion resistance than paints.

If you do want to use paint, polyester, polyurethane, epoxy, acrylic lacquer and oil-based formulas all provide an effective seal.

As well as providing an effective seal, many Exel customers use paint for its aesthetic properties. It also minimizes surface fading due to ultraviolet light exposure.


The best way to repair fractures of less than 10 cm / 4” is with splicing.

If a profile sustains a fracture of more than 10 cm / 4”, the best repair is to replace the entire section.

If replacement is not feasible, then the damaged section must be repaired to maintain its structural integrity. Failure to do so may result in the fracture worsening and affecting the entire structure.

The following will show you how to splice a small fracture in a wide flange beam. The basic technique is the same for most splicing repairs but please consult Exel for specific guidance.

Before you start, ensure you have selected splicing profiles strong enough for the application and, if possible, in the same color as the original.

We will use angles on each side of the beg/flange interface and the flat sheet at the flange’s back.

  1. Cut the angles and plate you intend to use as a splice 15cm / 6” longer than the fracture
  2. Trace the outline of the splicing profiles onto the damaged profile and sand the area within your traced outline
  3. If clamping is difficult, you can use bolts to mechanically hold the splice. Place the profiles in position and pre-drill holes for the bolts. Pre-drilling will minimize movement of the profiles after the epoxy adhesive has been applied
  4. Mix enough epoxy adhesive to cover all of the bonding surfaces. Make sure to follow the manufacturer’s guidelines and take proper precautions to avoid fume inhalation
  5. Spread the adhesive over both the damaged profile and the splicing profiles. Immediately place the splicing profiles onto the damaged profile. Insert the bolts (if used) and tighten. Quickly remove excess adhesive from the repaired section before it cures
  6. Leave profiles to cure for 48 hours

Resin filling

Resin filling is a technique designed to repair very minor chips. If your composite is more severely fractured, it will require a splice repair.  Resin filling allows you to prevent the absorption of contaminants and retain functionality in a more cost-efficient way.

  1. Sand the damaged area to remove all loose material and to provide a good bonding surface. After sanding, clean the area and let it dry completely
  2. You will be using epoxy or catalyzed resin for this repair.
    – If epoxy is used, please refer to the section on gluing for mixing procedure
    – If catalyzed resin is used, prepare the mix by following the manufacturer’s directions. If desired, milled fiber, or another filler can be added to improve the workability of the filling paste.
    Pigment may be added to help your repair blend into its surroundings

NOTE:  The resin/catalyst ratio can be altered to account for ambient temperature. If the combination begins to ‘smoke’ the ratio of catalyst to resin is too high.  Make a new mix using less catalyst.

  1. Using a spatula or putty knife, fill the damaged area with your epoxy or resin mix
  2. Cover the repair with cellophane and press it together with your palms, massaging to remove trapped air
  3. Tape the cellophane securely into position to protect the repair while the resin cures
  4. After 24 hours, remove the tape and cellophane and carefully sand the repaired area. Finish off with a resin seal


To find out the extent of the damage, you will need to sand away the charred portion of the surface. If your composite has not been charred/discolored by the flames, it is unlikely to have sustained any functional damage.

After the charred area has been removed, the repair needed will depend on the size of the imperfection left behind.

At a minimum, the surface should be resealed; if the charred area is large and deep, the part should be replaced.

Glass lay-up

This technique only applies when the crack is small and structural integrity is not threatened. For anything more serious, please contact Exel.

  1. Sand the affected area. Tape down the sides, in a rough square, leaving a gap of 5-7cm / 2-3″ around the crack
  2. Remove all dust and clean the area to be repaired
  3. Cut a piece of glass mat that covers the sanded area, adding 1.5 / ½” margin around the edges
  4. Cut a piece of 10 mil veil to cover the sanded area. Multiple pieces may be used to overlap at joints
  5. Weigh the glass veil and mat. Measure out four times that weight in resin and add 1% – 5% of DDM catalyst, starting with 1%. Stir thoroughly. The pot life of this mixture is dependent upon the percent catalyst and the ambient temperature and must be determined on sight. Do not attempt to use catalyzed resin after it begins to gel. Always follow your catalyst manufacturer’s instructions
  6. Paint the sanded area with the resin/catalyst mixture
  7. Apply glass material and thoroughly wet with resin/catalyst mixture
  8. Add layers of glass and resin to obtain the desired repair thickness, removing air bubbles as you go
  9. Cover area with cellophane until the repair is cured
  10. Sand to a smooth finish and coat with resin mixture for corrosion protection

Hole filling

How you perform your hole depends on a number of factors:

  1. How structural load will be applied
  2. Your desired aesthetic
  3. The proximity of other holes

If the holes to be repaired is not close to any others, then you should use Fibrebolts. If there is another hole close to or intersecting the one being repaired, use the counterbore method.

  1. Drill the mislocated hole to the nearest tap size
  2. Tap the hole to the smallest Fibrebolt size you have
  3. Apply epoxy adhesive to both the Fibrebolt threads and the hole edges
  4. Screw the Fibrebolt into hole
  5. Cut the Fibrebolt as close to the material as possible
  6. Grind flush
  7. After epoxy has cured, reseal the area with resin

Note: This method works well when no other holes are near or intersect the hole to be repaired. If this is not the case for your repair, use the counterbore method.

  1. Using a flattened bit approximately twice the diameter of the hole, counterbore halfway through the material with the center of the counterbore aligned with the center of the mislocated hole
  2. Take a FPR plate half the thickness of the material being repaired and, using a hole saw, cut a plug for the counterbore. Sand the plug and epoxy it in place.  Let the adhesive cure
  3. Using the hole saw, cut another plug the same size as the original hole. Working from the opposite side of the material being repaired, epoxy this plug into place.  Let it cure
  4. Sand and reseal with resin as necessary


Follow this sequence:

  1. Acetone cleaning
  2. Shot blast with aluminum oxide. Acetone cleaning
  3. Apply primer treatment such as Dow-Corning Silane Z-6040

Follow this sequence:

  1. Acetone cleaning
  2. Shot blast with aluminum oxide. Acetone cleaning