Bob Meier of Mount Vernon, Ohio, asks:
"I need to repair an 80-gal fiberglass water tank that is leaking. What food-grade material would you recommend for this purpose? I’d like to use an inert substance that will seal the tank and reinforce the weak area without contaminating my drinking water."
Don Casey replies:
There are plenty of food-grade epoxy coatings available, but these are more for painting than repairing things. For a repair, I would use a quality epoxy resin, such as West System 105 or something similar. It seems unlikely you run much risk of making your tank less safe with an epoxy repair, the majority of which will presumably be made on the tank’s exterior. You should take the precaution of mixing the epoxy in a hardener-lean ratio to reduce the possibility of there being free hardener in the cured epoxy. If you are concerned about the new epoxy after the repair, you can always cover it afterwards with a food-grade epoxy coating.
Epoxy water tanks have been around for more than four decades, but it is notable that West does not recommend epoxy for drinking water tanks because of regulatory and safety issues. For an excellent perspective on the subject, I suggest you consult West’s online Epoxyworks article at epoxyworks.com/18/pdf/tanks.pdf. It includes advice as to the correct hardener ratio for a water-tank repair.