How to Get Rust Streaks out of Fiberglass

Nothing makes a fiberglass boat look uglier than rust streaks. And no matter how well built a boat is (including the use of 316-grade stainless steel for all the fittings) sooner or later those icky streaks are going to show up. Even on boats used primarily in freshwater, those orange stains ruin a boat’s good looks. Ready to zap ’em? Here’s how.

This center console was designed and built for saltwater use, but the speakers eventually spit forth a nasty plume of rust streaks.

The key is in the cleaner. Regular soaps and scrubbing have little to no effect on rust streaks; instead, you have to use a cleaner containing oxalic acid. There are plenty of these on the market: Davis FSR, Marykate On & Off, and West Marine Fiberglass Stain Remover, to name a few. But be careful about which you choose. Some, like MaryKate On & Off, are liquids. If your rust streak is on a vertical area, that makes it hard to use because you brush or wipe it on, and it merely runs off. Others, like Davis FSR, come in a jelly-like form. These stay put even when applied to a horizontal hullside, though you can’t cover nearly as large an area with the little jar of jelly.

Why should you care if it runs off the surface? Because the key to cleaning away rust streaks (and water streaks too, for that matter) with this stuff is to apply it, and let it sit for several minutes. There’s no scrubbing involved, but you have to give the acid time to do its thing. You also have to be careful with these cleaners, which means wearing latex gloves and taking care not to get it on your skin, or breath in the fumes.

And there’s one more caution: these cleaners are tough on the fiberglass, and need to be thoroughly rinsed away after use. If your boat is on a trailer, you have to be doubly careful—these acids chew away at metal in no time flat. Treat a hull then give it an insufficient rinse and leave an acidic residue all over your trailer, and you’ll soon be buying a new trailer. Some boaters even cover the trailer with plastic, prior to applying the cleaner.

With these issues, is it even worth using this stuff? Yes. If you have rust stains marring your pride and joy there simply is no other way to bring its looks back. So choose the best cleaner for the job, be careful with it, and after you’re done spend a good 10 or 15 minutes rinsing it away with the hose. Rust streaks, BE GONE!

Lenny Rudow: