How to Find and Fix Leaking Rivets on an Aluminum Boat

Some water in the bilge after a rainy day or a wet ride is normal. Watch how much comes in at the dock and how much comes in while running. Before you blame rivets, check the drain plug and its threads, livewell and bilge pump fittings, transducer and transom bolts, and the motor mounting bolts. Those leak just as often.

Pull the drain plug, let the boat drain, and sponge out the last of the water. Remove any floor panels you can so you can see the inside of the hull. Park the trailer level with the wheels chocked.

With a garden hose, put water inside the hull up to about the waterline, not higher, and only in one end at a time (tilt the trailer tongue if needed). A boat full of water is very heavy and can bend the hull or overload the trailer.

Now go underneath with a flashlight. Look for drips, wet streaks and tiny streams from each rivet row and seam. Fingertips are good at finding damp spots you cannot see. Circle every leak with a marker, and mark the big ones differently from the slow seepers. Drain the water when you are done and let the hull dry completely, ideally for a day or two.

• Seeping, tight rivet: the head is snug but water creeps past. Seal it (Step 7).
• Loose rivet: the head moves, sounds different when tapped, or has a dark gray "smoking" ring of oxide around it from rubbing. Tighten it (Step 6) or replace it (Step 8).
• Cracked, sheared or missing rivet, or a head eaten away by corrosion: replace it (Step 8).
• Crack in the hull, leaking weld, or a patch of pitted metal: stop and see "When to call a pro."

Scrape off old sealant, paint and goop around each marked rivet and seam, on the side you will work from. Scrub with a wire brush or abrasive pad until the aluminum is clean and shiny, then wipe with acetone or alcohol. Aluminum grows a new oxide skin quickly, so clean only the area you can finish the same day.

Solid rivets can often be snugged up again. One person holds a heavy steel block or bucking bar firmly against one head; the other taps the opposite head with a ball-peen hammer. Use many light taps, not hard blows. Old aluminum rivets can crack or split if you hit them hard.

Check after every few taps. If the rivet tightens, move on and seal it in Step 7. If it cracks, keeps moving, or the metal around it starts to dent, replace it instead.

A toughened, flexible epoxy made for aluminum (such as G/flex) works better than stiff epoxies or putties because it moves with the hull. The maker's method, in short:

• Work from the inside when you can, so gravity pulls the epoxy into the seam.
• Warm a short section of rivets or seam with a heat gun to drive out moisture and help the epoxy flow.
• Apply the mixed epoxy with a syringe around each rivet head and along the seam while the metal is warm, and keep warming gently until it wicks in. Do not heat it until it smokes or changes color.
• For bigger gaps or loose rivets, thicken the epoxy with the filler the maker recommends and press it in until it comes out the other side.

Let it cure fully before the boat goes in the water. The manufacturer's instructions say overnight at 65°F or warmer; follow the label of the product you use.

Drill out a bad rivet carefully: center punch the head, then drill just the head off with a bit the size of the rivet shank so you do not enlarge the hole. Punch the rest of the rivet out while your helper backs up the hull with a block.

Replace it with a rivet of the same material and size: a solid aluminum rivet bucked as in Step 6, or a closed-end aluminum blind (pop) rivet set in marine sealant. Never use open-end pop rivets (water leaks through the center) or steel rivets (they corrode the aluminum around them). If the hole has become oversized or cracked, ask a pro.

Once the epoxy and sealant are cured, prime bare aluminum with a primer made for aluminum and paint it to match. Never use copper-based antifouling paint on an aluminum hull. Copper and aluminum in water are a corrosion recipe.

Repeat the water test from Step 3, or launch the boat and leave it in the water for an hour or two while you watch the inside. Expect to touch up one or two rivets you missed; that is normal. Keep the bilge pump working and check it after each outing for the next few weeks.

• Adjust the trailer bunks or rollers so they support the hull along its length, without hard points under single rivet rows. Trailer maker Load Rite recommends slick bunk covers rather than carpet wherever bunks touch a metal hull, because wet carpet holds moisture against the aluminum.
• Slow down in chop. Pounding is what loosens rivets.
• Keep copper, brass and stray stainless parts (coins, fishing tackle, loose screws) out of the bilge.
• Check the outboard's anodes and, if the boat lives at a dock with shore power, read our anodes and shore power guides about galvanic corrosion.