I get people ring up and say they have stuck a panel into a car or completed a repair to a fairing on a bike - and then quite rightly used a woven glass or carbon tape to go over the join. They clean/sand the area properly and mix their resin with a little coloidal silica or microfibres to give it some resistance to sag. They cut the tapes, laminate them in and use peel-ply to keep the whole lot consolidated while it cures. All text book stuff. The job looks a peach when they peel the peel-ply off, but within a few weeks the cracks have started. Why when it was going so well!!
Y'see, standard tape is fine for most secondary bonding (ie the reinforcement laid up after the glue sticking the panels has cured), but as it is 0/90 oriented (ie the fibres run at 0 degrees and 90 degrees to the length of the tape) it has a big failing - Only half of the fibre is doing any work... The '0' degree fibres are running the length of the join and aren't doing anything...
In higher loaded areas, for example on the deck of an 18ft skiff where 3 blokes will run around while the boat bounces up and down, it is best not to leave too much to chance. As watertight and solid as it feels, 0/90 standard taping isn't enough. Instead we took some time and cut some 45deg/45deg tapes from a metre of standard woven fabric - in this case a 200g/sqm carbon fabric. Lay up, peel ply, wash up and rest assured that all of the fibre is doing something to hold the deck together - and consider torsional or sheer case loading, the fibre is more directly resistant to loads. Savvy?
(I'm going to be running around on that bit very soon!)
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