Oriented strandboard was sanded and roller-coated with UV-cured finishes. The effects of these treatments on the surface roughness, dimensional stability and fire resistance of OSB were assessed. Sanding reduced the average roughness of OSB, but it had a smaller effect on maximum roughness because sanded boards still contained surface voids between some strands. Sanded boards absorbed less than half of the coating material of unsanded boards, and when they were finished with a UV-cured coating system consisting of filler, sealer and two top-coats they absorbed less water and were almost as dimensionally stable as unsanded and coated boards. The swelling of coated boards after 72 h immersion in water was less than one third of that of uncoated OSB. This reduction in swelling compares favourably with that which can be achieved using chemical or thermal modification of OSB. Coated boards were more fire resistant than uncoated ones, but sanding reduced the fire resistance of OSB (coated and uncoated), possibly because it removed part of the densified surface layer from panels. Hence, we conclude that light surface sanding makes it easier and more economical to apply moisture resistant finishes to OSB using roller coating, but it should not be used prior to application of fire-retardant finishes.

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