Nature of knot checks developed during seasoning of radiata pine sawn boards

Abstract

One hundred and sixty radiata pine boards were dried using different methods (air drying, commercial kiln drying and laboratory kiln drying) to study the effect of knot, wood and seasoning variables on the nature of knot checking. Among the knot variables, the largest knot group (diameter> 75 mm) was found associated with the highest check rate and the most severe checks. Medium size group (25 mm < diameter ≤75 mm) had significantly lower check rate. Face knots were significantly more liable to cracking than any type else. The major check directions of a knot generally ran across the symmetrical axes of the knot. In wood variables, due to lower number of medium size knots butt half had higher check rate than upper part of stem. After studying the density and check ratio of northern outer wood, southern outer wood and core wood, a reverse relation was found between the density and the check ratio. Final moisture content affected knot checking directly because it is proportional to shrinkage. Temperature did not show significant influence. Air dried timbers, especially those exposed to air without shield, had more severe checks than those exposed to other drying conditions. There were no relationships found among sawn pattern, dimensions of boards and check rate of knots.