DIY Marine Fiberglass repairs?

Question

I have a fiberglass boat which keeps taking in water from the area around the bung. I have tried to repair it with fiberglass but don't seem to be having much luck::( Can anyone offer me some advice? Thanks

Answer 1

You are better off to forget trying to work around the existing bung. This repair is best accomplished with just boat epoxy - you don't even need to mess with fiberglass cloth unless for some reason you want to.  In the past, I have simply cleaned out the bung and fastener holes, then epoxed in a snug fitting wooden plug. Let it totally cure, then sand your brains out until you get it all flush and smooth.  Now the bung hole is repaired.  If you want to use fiberglass over the repaired bung, now is the time; but no need really.  If you are using actual "boat" epoxy, this stuff is what adds strength to the fiberglass, it is not the other way around - as in the case with the old polyester method.  So... either way, you repair the bung first, fiberglass over it if you desire; then re-drill and install a new bung.  I assure you, this is really the only way you are going to get a smooth finish and a problem free repair.

Answer 2

I'm a power boater (stinkpotter to some), so I'm not sure where the bung is, but I do know that fiberglass is in two different forms polyester and epoxy.  Polyester is generally mixed as a large portion of resin to a very small portion of hardener.  It cures very quickly - 20 minutes to tack free a few hours to near full strength.  It is normally used with fiberglass mat to obtain strength and some flexibility.  Epoxy is generally a 50/50 mix and cures very slowly - 2 to 4 hours to tack free and usually at least 24 hours before use.  It is much more flexible after curing, and use of glass or mat will make it even stronger.

My guess is if you are in fact getting the resin where the leak is, that you are using polyester and no mat or cloth backing to give it strength.  A coat of polyester will crack pretty quickly under stress.

Epoxy is much more flexible, however if you can, you should also use fiberglass mat or cloth with it as this will give a stronger repair.

Note the area has to be very clean.  After cleaning the surface of dirt etc, use a special pre prep solution or at a minimum lacquer thinner.  If possible before using the prep solution you should sand the area to give the fiberglass resin something to bite into.

One final note, you can put epoxy over polyester, but not polyester over epoxy.  So if the epoxy doesn't work for you, you can't just go back with more polyester.

Also please remember water frequently does not come from where it shows up e.g. make sure the bung isn't just the place where it is leaking out, but not the place it is leaking in.  Many repairs are made to the wrong place because water simply seeks the path of least resistance, so water coming in via a poorly caulked area, might actually show up 2 or 4 feet away at a weaker point in the overall structure.

By the way newer cars like the Corvette and I suspect newer boats aren't polyester fiberglass like the old days, they are SMC sheet molded compound, and as such can only be repaired with epoxy as polyester won't stick at all.  Even epoxy doesn't work on all of these materials.

Good luck.

Answer 3

I had a similar Problem with my boat, The bung was laking, I Figured because it was leaking it was loose, I taped on it with a small Flat punch and sure enough it slid rite out, I replaced it with a new one using 3M 5200 Fast cure Sealant,

(West Marine)

scored the new one with a 180 grit sandpaper made sure the Hole was Dry and sanded clean and no more Problems,  don't worry about the left over sealant, it works very well around the house also.

Answer 4

I'm not clear on what's up with your boat, so good advice is a shot in the dark.

Post an image of the problem area for some advice that might help you.