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When building very large objects, such as an airplane wing, it no longer becomes reasonable to hand lay epoxy. In these cases pre-impregnated carbon fabrics are used (prepregs). Since the epoxy resin & hardener must be combined in prepreg fabrics, typically a temperature threshold must be met in order for the resin to cure (ex. 250-550 Degrees F). Epoxy’s theoretical max temp is 600F. The highest temp of a 2-part epoxy is (as of this writing) is ~215-225F (Adtech 820, sold on our epoxy page).
II. Advantages of Prepregs
The lack of need to mix the epoxy and the consistent amount of resin per sq area is the primary advantage of pre-pregging. Epoxy resins are also available that can be used specifically tailored for very large applications.
III. Disadvantages of Prepregs
Prepregs typically must be refrigerated until they are used. They cost much more than buying epoxy and hand laying the resin. They typically have a short shelf life (6 months is common).
It is common for prepregs not to be clear or UV stable (will yellow if exposed to UV), although there are exceptions.
Prepregs should only be used when they are needed. If you can get by without prepregs, typically this is your best option.