Mechanical Properties of Polysiloxane Topcoats Available to Purchase

Results from laboratory and field investigations of the mechanical characteristics of protective coatings are summarized. Lack of paint film flexibility and strength, together with internal stress and low adhesion, are expected to be the main reasons for the cracking and flaking of protective coatings. Internal stresses were discussed in previous work, and adhesion will be discussed in the third and final paper of this series. Changes in mechanical properties from exposure offshore and from artificial aging in the laboratory have been studied. The individual coatings from two three-coat systems and two additional topcoats were included in the test program. The tested coatings were commercially available products and all topcoats were polysiloxanes. The tests have shown that there are significant differences in the mechanical characteristics of the polysiloxane topcoats, and that the impact of offshore exposure or weathering in the laboratory varies between the coatings. The internal stresses reported in the first paper of this series could not cause cracking of any of the tested products. However, the results indicate that the vulnerability to external strain varies.