Recoating Plastisol/PVF2

A wide variety of organic coatings, classifiable as plastics, are used on metal cladding and other components. These can be overcoated (post-applied coating) for aesthetic or maintenance purposes at or near end of life.

The individual types vary and include PVC plastisol, PVF2 (PVDF), polyester and polyurethane. Powder coatings such as epoxy, polyurethane, polyester or silicone modified versions are also found.

It is essential that the pre-coating be identified to enable the application of a correctly adhering overcoating system, to be applied with or without a primer. Visual identification is not straightforward, but older PVC exhibits a characteristic ripple and polyester can be glossy, the others all appear smooth and generally matt. FTIR spectroscopy should be used to identify samples from site.

Manufacturers provide information on suitable primers and top coat(s) and this should include provision for painting any bare metal e.g. edges or patches.

Identification

When identification is not possible, a site adhesion test should be undertaken with the range of primers available and also a direct application. The test should be done on cleaned areas (see 7.15.4) and in accordance with the coatings and manufacturers instructions. This might involve leaving the overcoating systems for up to 7 days to allow adhesion to develop via plasticiser linkage on PVC for example.