Adhesive Bonding of Non-Structural Panels

Advancements in chemical technology have enabled manufacturers of adhesive materials to develop formulations tailored specifically for bonding sheet metal and aluminum body panels. Although adhesives have been used in the repair industry for some time in the bonding of replacement outer door panels, new formulations are now available for bonding sheet steel, as well as aluminum quarter panels, rear body panels, wheel housings and roof panels.

Tech-Cor Research has been involved with the bonding of both quarter panels and rear body panels on vehicles that were subsequently crash tested by an independent research facility. The adhesives used are capable of providing an extremely strong bond and have undergone testing for fatigue, strength, corrosion resistance, delamination and exposure to humidity and temperature extremes.

Advantages of adhesive bonding include an even distribution of load eliminating stress concentrations, an environmental seal that eliminates the need for additional seam sealing and improved resistance to corrosion at the panel flanges.

While development of adhesive formulations for use on load-bearing structural members continues, the adhesives available to the repair industry at this time are intended only for the bonding of non-structural body panels (i.e., door outer, quarter and rear body panels and roof).

Adhesive formulations different by manufacturers with some being urethane based while others are acrylic. Specific attention must be paid to the individual manufacturer's instructions regarding both open (working) and cure times. Some adhesives cure at ambient temperatures, while others require a specified amount of heat to initiate the cure cycle.

Prior to using an adhesive, the paint and primer must be removed from the mating flanges on both the vehicle and the replacement panel in the location where the bond areas will occur. A plastic coated abrasive wheel should be used for this operation to avoid removing any pre-existing galvanized coating. Grinding discs should not be used because they will remove the base metal. The individual adhesive manufacturer's instructions should be followed, since certain adhesive products do not require removal of the E-coat on replacement panels.

After all the mating surfaces have been cleaned, the replacement panel should be positioned on the vehicle, properly aligned and the bond areas marked. Holes for sheet metal screws are then drilled through both the panel and the mating surface of the existing flange at points where clamping will be inaccessible. The sheet metal screws, used in conjunction with clamps, will hold the panel in proper alignment during the curing process. The panel can then be removed for final cleaning prior to application of the adhesive.

Since the shelf life of various adhesives differ, the date on the container must be checked before use. Working time should be noted prior to application of the adhesive.

Once the adhesive is applied to both the replacement panel and the flanges on the vehicle, the panel can be installed. If repositioning is required after installation, it is important that the bonded areas not be separated. The panel should be slid to achieve proper alignment.

After the replacement panel is clamped and screwed in its proper position, excess adhesive that is squeezed out should be removed along the bonded seams. To achieve optimum results, the individual manufacturer's instructions should be followed precisely regarding the amount of adhesive used, as well as clamping pressure. Note that if excessive clamping pressure is used, the bond may be compromised.

Once the adhesive has cured, the sheet metal screws should be removed and additional adhesive applied to fill the holes that were drilled. At this time any drain holes that may have become clogged with adhesive should be cleared.

Ordinary plastic body filler should not be used over any bond seams because of poor adhesion characteristics. If additional filling is required, the specific product recommended by the adhesive manufacturer must be used.

Since no additional seam sealing is required, normal refinishing procedures can then be employed to complete the repair process.

The information provided in this bulletin is for educational purposes only. Although every effort has been made to ensure the accuracy of the information contained in this bulletin, Tech-Cor assumes no responsibility or liability for any repairs performed using information from any publication issued by Tech-Cor.

Any person performing repairs must determine whether any suggested or recommended procedures or repairs are suitable or appropriate for the particular vehicle being repaired. The repairer remains solely responsible for such determination, as well as for the proper completion of the repairs.

Reproduction of this bulletin is not permitted without the written approval of Tech-Cor.