ASA and PSIA Instructor
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I've done this job three times with West System epoxy, including a R19. West System is the way to go, as it is much harder than Interprotect, and will protect steel much better. Apply directly to freshly ground metal. Five coats is good. Use microballons for filler, it is much easier to sand than colloidal silica. Put the final coat of epoxy over the filler.
Interprotect is formulated for easy application over large areas ( the hull) and ends up being a little soft, you can crease it with your fingernail. Good for the hull, but not for steel.
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