Weatherability of water-borne wood preservative semi-transparent coatings(II) -Performance of coatings after re-finishing without removing old finish

To examine the effects of re-finishing on the performance of wood preservative semitransparent coatings, sugi heartwood specimens that had been once finished with several coatings (6 water-borne and 2 solvent-borne commercial products) and then weathered for 24 months at 45 degrees facing south in Tsukuba (Exposure I) were re-finished with the same coatings as before without removing old coat, and then exposed to the weather again for an additional 24 months (Exposure II). For all the coatings, the mean coating weight (wet, g/m2) of re-finishing was larger than that of initial (previous) finishing. The color of re-finished surfaces was characterized by decreases in both lightness (L*) and chromatic values (a*, b*) compared with initial finishing for most of the coatings. Color changes during Exposure II were smaller than those of Exposure I for all the coatings. Water repellency was higher during Exposure II than Exposure I for most of the coatings. These results may be due to the effects of increased absorption of coatings at the re-finishing. On the other hand, no distinct differences were found in surface defects between Exposures I and II. It was also found that, for each of these performance tests, the relative order of performance among the coatings tended to be unchanged from Exposure I to Exposure II.