In Norwegian workshops the standard pre-treatment procedures for steel structures intended for sub-sea use, normally include removal of shop primer by blast cleaning to Sa 2 1/2 before application of corrosion protective coatings. This is also stated in the Norwegian offshore standard NORSOK /1/. Omitting this stage in fabrication will represent large reductions in both time consumption and costs, and reduce the volume of waste from the blast cleaning. This report presents results from investigations of how a shop primer will influence on the coating properties. The aim of the investigation was to test whether the systems are good enough if the shop primer is left on the surface. Two different zinc silicate shop primers have been included in the investigation. As protective coatings we have used three different epoxy mastic systems with Al pigments. In addition to panels with original shop primer, we have also tested shop primed panels pre-treated in various ways, such as
heated, corroded and blast cleaned to various degrees before coating. The coatings have been tested in the ASTM-G8 /2/ test and in a long term test in sea water polarised with a Zn anode. We have found that coatings including the zinc silicate shop primer are more susceptible to cathodic disbonding than the coating applied directly on blast cleaned steel. It is however possible to meet the NORSOK criteria with a zinc silicate shop primer as first coat. Keywords: Shop primer, cathodic disbonding, coating performance.