Durability of varnishes - are subjective assessments enough?

Abstract

This paper is based on a study of the protection performance of varnishes applied to a wooden substrate for outdoor exposure. The aim of the work was the evaluation of some of the test methods that are often used in the coating industry to determine the durability of coating systems: determination of film thickness, designation of quantity and size of defects, and of intensity of uniform changes in appearance; determination of specular gloss and colour measurement. The methods were applied to eight varnish systems (with and without colorants and light stabilizers) that were subjected to artificial weathering and to natural weathering in outdoor exposure. The test methods used, to evaluate the appearance and physical-chemical properties of the coating during its degradation, seem to be able to select the best varnish formulation to the protection of wood for exterior uses and gave also an idea about their usefulness.