Follow these guidelines when performing sheet molded compound (SMC) repairs:
Clean, scuff, and wipe all the areas to be repaired with a naptha solvent.
For added strength and durability, dish cove and reinforce at least 1 side of SMC joints using a tacky mesh tape or equivalent.
When partial panel replacement is performed, use 50 mm (2 in) backing patches made from SMC as a reinforcement for all the butt joints.
<LI type=1>Scuff the area where repair is to be performed. <LI type=1>Clean the bond area with a lint-free rag using naptha solvent. <LI type=1>Cracks in SMC should be dish cove and reinforced on at least 1 side using a tacky mesh tape or equivalent. <LI type=1>Sectioning joints require backing strips 50 mm (2 in) wide, which can be cut from leftover pieces of SMC. <LI type=1>Apply a thin coat of Goodwrench Structural Bonding Epoxy GM P/N 12345726 (Canadian P/N 88901676) or equivalent, to the entire joint area extending across the cut lines and across the backing strip.
Use tacky mesh tape or an equivalent reinforcement matting.
Allow to cure according to the adhesive manufacturer's recommendations.
Shape and refinish the repair areas as necessary to resemble the original appearance.
Prepare the surfaces to be bonded according to adhesive manufacturer's recommendations. Many adhesive manufacturers have different preparation methods.
<LI type=1>Use supplies and repair materials from the same manufacturer. Do not intermix systems. Mixing materials from different manufacturers can produce unsatisfactory results. <LI type=1>Ensure that the surface is clean and dry before applying adhesive. <LI type=1>Apply a consistent adhesive bond to the prepared surfaces. <LI type=1>Mechanically retain the panel in place in order to wet out the adhesive along the entire bonding surface.
Allow the area to cure according to the adhesive manufacturer's recommendations.
Plastic parts can be identified by the SAE code, which is usually found on the rear of the part, and/or by the characteristics of the plastic. Knowing the type of plastic aids in selecting the proper repair materials and in selecting the proper repair procedure.
Look for the SAE code stamped into the part.
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<LI type=1>Match the code to those in the plastic identification chart to determine whether the plastic is thermoplastic or thermoset plastic, and whether the plastic is rigid or flexible. Refer to Plastic Identification and Refinishing Systems .
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Do NOT use a plastic burn test to distinguish the type of plastic. The burn test produces vapors which are harmful.
Perform 1 or both of the following tests to determine if the part is thermoplastic polyolefin or thermoset non-polyolefin.
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<LI type=1>Cut a shaving of plastic from the back of the part. The shaving should be free of mold release agents and paint.
Place the shaving in a container of water.
Thermoplastic polyolefin floats
Thermoset non-polyolefin sinks
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Sand a spot near the damaged with Grade 36 Roloc Disc.
Thermoplastic polyolefin material melts or frays when sanded.
Thermoset non-polyolefin material sands cleanly.
Thermoplastic and thermoset plastics can be either rigid or flexible. Thermoplastic plastic parts are best repaired with a hot iron plastic material-feed welder, but are usually replaced. Thermoset plastic can be repaired with epoxy or other more rigid 2 package repair material.
The following procedures should be followed when repairing all types of thermoset plastic:
<LI type=1>Use the supplies and the repair materials from the same manufacturer. Do not intermix systems. Mixing materials from different manufacturers can produce unsatisfactory results. <LI type=1>Clean the inner and outer surfaces of the repair area with a soap impregnated scouring pad in order to remove any dirt or mold release agent. A mold release agent is used during manufacturing in order to prevent the part from sticking to the mold. This release agent may be present in large enough concentrations to affect adhesion. <LI type=1>After washing, clean the area a second time with naptha solvent. Use only enough of the remover to dampen a cloth. Too much of the solvent will saturate the panel and may migrate out later, affecting the finish. Use a tack rag and air for finish cleanup. Allow the panel to dry thoroughly. <LI type=1>Apply force around the damaged area in order to look for hidden damage such as hairline cracks. Small cracks and faults in the bonds and the panels will eventually grow larger if left unattended. Drill a 3 mm (1/8 in) hole at each end of a crack in order to prevent any further cracking. <LI type=1>Remove the surface finish from the area to be repaired. Adhesives are designed to adhere to the plastic substrate, not the finish. Important
Some adhesives require the use of a primer when bonding to metal. Use only the primers that are approved by the manufacturer's. If you are bonding a composite panel to a metal surface, follow the adhesive manufacturers recommendations on how the metal should be prepared.
<LI type=1>Repair the inner surface of the panel first. <LI type=1>When using a mat reinforcement to repair the inner or outer surface of a panel, inspect that there are no strands of the mat left uncovered or unsaturated with the repair material. If exposed, the mat may act as a wick and draw moisture into the repair area, affecting the integrity and the finish. <LI type=1>Inspect the rear of the damaged panel for tool clearance. If accessing the repair with a saturation roller, a grinder, or a sander is impossible, do the repairs by hand. <LI type=1>Align the damaged or spliced area with a brace and clamps if the damage is severe. For a smaller repair, use a heavy tape on the outer surface in order to maintain the alignment until the inner repair material has cured. <LI type=1>If welding is necessary, do not allow the flame or the welding heat to come into direct contact with the plastic body panels. Protect the surrounding area with a fire retardant fabric. Several layers of aluminum foil make an excellent heat shield if not in direct contact with the flame. <LI type=1>Inspect the rear side of the work area before making repairs in order to avoid possible damage to wires, motors, etc. <LI type=1>Composite parts will not yield or take a set as with steel parts, thus they cannot be straightened. If poor alignments are suspected, due to a collision or other damage inspect the steel reinforcements for damage and replace or repair them before repairing the plastic parts. <LI type=1>Save any useful size pieces of repair material when cleaning up the work area. These pieces can be used for reinforcing smaller repair areas.
Force dry structural bonding epoxy with heat. Heat speeds the cure time and increases the bond strength. Follow the manufacturers curing recommendations.