balsa wood

Balsa Knots

Balsa knots occur when a tree limb grows in the side of the harvested block.  Normally long blocks will have this sort of defect.  The tree limbs usually are very high off the ground allowing for better knot-free blocks than a pine tree would have.

There are also some defects that may happen around the area of a knot or randomly without warning.  Sometimes the grain direction changes in a balsa block.  Once this happens the affected area looses its strength.  The balsa has "slanted grain" and can be seen by a drastic change in the grain direction.  For example grain that goes across an 1/8-inch square stick for about a length of 3/4 inch or shorter across the side would be considered slanted grain.