Hardening of bonding systems

A composite structure comprising:

• a mat of ligno-cellulosic materials having at least:
• a first layer of the ligno-cellulosic materials combined with a first glue mix, the first glue mix of the first layer including a resin based on at least one of formaldehyde and polymeric isocyanate;
• a second layer of the ligno-cellulosic materials combined with a second glue mix, the second glue mix of the second layer also including the resin based on at least one of formaldehyde and polymeric isocyanate;
• and a third layer of the ligno-cellulosic materials combined with a third glue mix, the third glue mix of the third layer also including the resin based on at least one of formaldehyde and polymeric isocyanate;
• a resin hardener formed by a salt having an acid moiety and a base moiety;
• wherein one of the acid moiety and the base moiety of the resin hardener is a more volatile moiety, the more volatile moiety activating hardening of the resin in the first glue mix of the first layer upon vaporization;
• wherein the second and third layers are surface layers of the mat and the first layer is a core layer located therebetween;
• and
• wherein the resin hardener is not in the first glue mix of the first layer, the resin hardener being instead either:
• sprayed onto only outer surfaces of surface layers of the mat;
• or
• included in the second and third glue mixes of the second and third layer of the ligno-cellulosic materials, respectively.