**2.4 Preparation of panels**

SAE 1010 steel panels were previously degreased with solvent in vapor phase; then they were sandblasted to ASa 2½ grade (SIS Specification 05 59 00/67) obtaining 25 µm maximum roughness Rm. The application was made in a single layer reaching a dry film thickness between 75 and 80 µm. In all cases, and to ensure the film curing before beginning the tests, the specimens were kept in controlled laboratory conditions (25±2 ºC and 65±5% relative humidity) for seven days.

The study was statistically treated according to the following factorial design: 2 (type of binder) x 2 (average diameter of spherical microzinc particles) x 3 (type of reinforcement fibers) x 3 (level of reinforcement fibers) x 6 (PVC values), which make 216 combinations. In addition, reference primers (without reinforcement fiber) based on both binders and both spherical microzinc particles for the six mentioned PVC values were also considered, which means in total 24 reference primers. All panels were prepared in duplicate; primer identification is displayed in Table 1.
