-- Last Updated: Dec-17-12 6:39 PM EST --
by which they meant that some layers were at 45 degrees. Whitewater layup experts don't seem to do that, but in shorter ww canoes and kayaks, subsequent layers are unlikely to have fiber orientation absolutely parallel to earlier layers. In examining broken composite boats, I haven't seen clear evidence of breaking along the line of cloth fibers.
Glass mat is ok for sea kayaks, because their hulls are not likely to be deformed as severely as ww kayaks. But I don't know of any ww composite boat builders over the last several decades who have incorporated glass mat. That speaks for itself. It might be used to stiffen ww canoe bottoms, but Kaz of Millbrook uses Spheretex instead, which is a cloth infiltrated with tiny polyester bubbles.
Glass mat is typically coated with a substance to which epoxy does not adhere well. Those building or patching with glass mat should use vinylester instead.