Before we consider any internal reinforcement, we must consider how we are going to bond this to the hull. The term secondary bonding refers to any laminating where you are adding to the cured laminate.   For instance, where you are installing a bulkhead, a web floor, a stringer or a rib, you would be making a secondary bond.

   If you find it necessary to stop work on your basic laminate for over 48 hours, you will have to make a secondary bond when you recommence the laminating process, although I doubt if most builders would class it as such.   Usually, a secondary bond can be as good as a primary bond as long as proper preparation has been made.

   In practical terms, it is impossible to build a fibreglass boat without incurring many situations where secondary bonding is required.   Providing you understand the process and take due care, there is no reason to expect any problems during construction, or when the boat is finished.  

   There are several things you can do to prepare a fibreglass hull for secondary bonding. In all cases you should sand the primary part so that no shiny surface, dirt or any other foreign material remains where the new part is to be bonded in place.    In addition, the hull interior surface can be wiped with styrene or acetone to remove any impurities and help key the surface for further laminating but, you should talk to your materials supplier about this to obtain the best recommended methods for any particular brand of resin or climatic condition.     Always prime coat plywood before you bond it into place.