Home Detailed application Technical Detail Bonding GRP to Metal - Technical Detail

Bonding GRP to Metal - Technical Detail

Application Instructions

Polyester resins are poor adhesives and rely on the porosity of the substrate to affect a good bond, the bond to metals is poor. There is also the additional problem of differential expansion due to the difference of the coefficient of expansion between steel and GRP.

To overcome this problem there needs to be a good bond between the GRP and metal substrate which will remain flexible and tolerate the differential movement between the two dis-similar materials.

This can be achieved by using a moisture cured PU adhesive sealant trapped between the 2 materials as shown below:



Thoroughly clean the metal surface to be bonded onto. Remove all paint, rust etc., unless it is a coated metal and ensure that the surface is clean and dry. It is best to wipe the surface with acetone to ensure no contamination.


Using a skeleton gun, apply generous strips of PU adhesive onto the metal to be laminated over. Where water will be running over this bonded area, or if this area is to be submerged, use 3 parallel beads in order to ensure complete sealing round the perimeter.

Immediately apply the CSM to the surface of the beads and rub into place. A more effective seal may be achieved by using a small consolidation roller to ensure that the adhesive is fully consolidated into the glass.

Leave to cure for about 2 hours. The PU is moisture cured and the curing reaction must finish before the laminate is applied over the top of the CSM. Apply resin to the CSM and form a laminate.

For larger areas, it is necessary to first form a seal around the perimeter of the area using the technique outlined above with 3 parallel strips of PU adhesive. A 100mm wide strip of bandage should be rolled over the top of the PU adhesive using a consolidation roller to ensure a good seal. Fixing points at 200mm centres or less (depending on the complexity of the area) should be formed using 100mm square cuts of bandaged consolidated to several beads of PU adhesive. A GRP laminate can then be bonded to the top of the roof. The perimeter area should form a water tight seal around the area, the PU adhesive allows for differential expansion between the two materials.


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