Fiberglass Tank Fix (2011)

Im a new member with question pls....what sealant recommended for the threaded joints in fiberglass tank for the steel /brass petcock inserts.
The permatex aviation sealant spec sheet says its not for use on plastics,
so does that mean its not good for fiberglass threads? What is best for the
fbrglss mated with steel threaded joints? Thks much!

PeoriaCommando13 said:

Im a new member with question pls....what sealant recommended for the threaded joints in fiberglass tank for the steel /brass petcock inserts.
The permatex aviation sealant spec sheet says its not for use on plastics,
so does that mean its not good for fiberglass threads? What is best for the
fbrglss mated with steel threaded joints? Thks much!

Click to expand...

For high performance sail boats when we need to embed metal into fiberglass, it is best to use a high quality epoxy resin thickened with materials selected for the required bond characteristics. For a brass or stainless tube threaded into a fiberglass hole I'd go with a high density filler to help reinforce the threads. I use West System epoxy and their various fillers. You can get small blister packs of this at most marine supply shops. Be sure to thoroughly degrease the tank and petcock threads. I'd also scuff up the metal threads with steel wool to help make a better bond.

Other epoxy brands should also be ok but it is best to use long cure time mixes not five minute stuff. Heating with a hair dryer for an hour or two after an overnight cure will maximize cross linking and give best possible strength.
If you want to ensure easy future unthreading of the part, you can use a release agent like cooking nonstick spray or even light oil on the metal before applying the epoxy. This will not affect the curing.

Rereading PeoriaCommando13 post above I see he was asking about just sealing threaded metal into glass tank. When doing such with metal tank all that is needed is the dowty type rubber sealing washers between tank and petcock fitting. Hylomar Blue is claimed to be fuel resistance and since it does not cure or harden it should also make a good thread sealant here.
Teflon plumbers tape should also work well.