How to Find and Fix Leaking Deck Hardware (Rebedding Cleats, Stanchions and Tracks)

Water travels along the underside of the deck before it drips, so the drip is often not under the leak. Dry the area inside completely. Then have a helper below with a flashlight while you run a gentle stream from a hose around one fitting at a time, starting at the lowest one and working up. Give each fitting a few minutes before moving on. Mark every fitting that shows water.

With the fitting still in place, press and tap the deck around it with the handle of a screwdriver. A dull, soft or "dead" sound, a spongy feel, or cracks radiating out from the base suggest wet or broken core. Note the size of the suspect area. A small damp ring right around the bolt holes is a DIY fix. A large soft area is not (see "When to call a pro").

Have your helper hold the nut below while you turn the bolt head from above (or the other way around if the head is hidden under a plug). Use penetrating oil on corroded threads and give it time. If a bolt spins and will not come out, stop and get help before you chew up the deck. Keep the parts in labeled bags so each fitting goes back in its own spot.

Slide a thin putty knife under the edge and work it around slowly. If the original builder used a strong adhesive sealant (polyurethane such as 3M 5200), the fitting can be bonded tight. Do not lever it off with a screwdriver: you can tear out gelcoat. BoatUS suggests a debonding solvent made for polyurethane sealants. If you use heat, keep the fiberglass cool enough to touch.

Scrape every bit of old sealant off the deck and the underside of the fitting, including inside the bolt holes. New sealant sticks to old sealant, not to the boat, so leftovers mean a new leak. Finish with a solvent wipe, changing rags as they get dirty. Cruising World points out that brand-new hardware and bolts often carry polishing wax or oil, so wipe them too. If the old bedding was silicone, acetone will not remove the film; sand it off.

This is the step that protects the deck for good. For each bolt hole in a cored deck:

• Tape the hole closed from below.
• Ream out the core around the hole sideways with a bent nail in a drill, or drill the hole oversize through the top skin and core only. Vacuum out the debris.
• Fill the hole with mixed, unthickened epoxy, let it soak into the exposed core for a few minutes, then let the excess drain out.
• Thicken more epoxy with colloidal silica to about mayonnaise consistency and fill the hole flush.
• Let it cure fully, then drill the bolt hole back through the center of the epoxy plug.

The bolt now passes through solid epoxy instead of bare wood or balsa, so water cannot reach the core and the deck will not crush when you tighten the nuts. If the drill shavings came out wet or dark, let the area dry out first and see "When to call a pro".

• Butyl tape: Never hardens and stays flexible, easy to clean up, and the fitting can come off again later. BoatUS likes it under bolted cleats and stanchions where the bolt can be held still and tightened with a nut. It is a poor choice under screws, because a turning screw drags the tape out of place. Buy tape sold for marine use.
• Polysulfide (for example BoatLIFE Life-Calk): Stays flexible, works above and below the waterline, and the fitting can be removed later. It can attack some plastics such as polycarbonate (Lexan) and PVC, so do not use it on plastic parts.
• Polyurethane adhesive sealant (for example 3M 5200): Very strong glue. Great for joints that should never come apart, but it makes the fitting very hard to remove next time. Avoid it on hardware you may need to rebed. 3M's 4200 line is sold as a medium-strength version that still lets parts come apart later; check the label of whatever you buy.
• Hybrid UV-resistant sealant (for example 3M 4000 UV): 3M describes it as a medium-strength, color-stable sealant made for topside parts that sit in the sun, such as hardware, hatches and portlights, that can still be disassembled after years of use. A good middle ground for exposed fittings where looks matter.
• Silicone: Flexible, but it does not stick very strongly, and paint and varnish will not stick anywhere silicone has touched. Pros treat it as an above-the-waterline product at best. Do not use it for anything below the waterline, and keep it off surfaces you may paint or varnish later.

Whatever you choose, read the label for temperature limits, cure times and the cleanup solvent.

Put a small countersink (chamfer) on the top edge of each bolt hole in the deck. This leaves a little pocket that fills with sealant and works like an O-ring around the bolt, and it helps stop the gelcoat from cracking at the edge of the hole. Dry-fit the fitting, bolts, backing plate and nuts to be sure everything lines up before any sealant comes out of the tube.

Trace around the fitting on painter's tape, cut along the line with a knife and peel out the inner piece, so the squeeze-out lands on tape. Then:

• Liquid sealant: cover the whole base of the fitting, not just a ring around the edge, and put a ring of sealant under each bolt head.
• Butyl tape: lay a strip around the base and wrap a small rope of tape under each bolt head so it fills the countersink. Warm the tape a little in cold weather so it squeezes out.

Do not put sealant on the backing plate, washers or nuts underneath. If the top seal ever fails, you want the water to drip into the cabin where you will see it, not get trapped around the bolt in the core.

Tighten evenly in a criss-cross pattern until you see a continuous bead of squeeze-out all the way around. Turn the nuts below, not the bolt heads, so you do not twist the sealant around the bolt.

• With polysulfide or polyurethane, many experts (including Don Casey for BoatUS) snug the bolts only, let the sealant firm up, then do the final tightening the next day so the cured sealant stays under compression. Others tighten fully right away. Follow the sealant maker's instructions.
• With butyl tape, tighten gradually and come back over a day or two to take up more as the tape flows.

Do not crank down so hard that the backing plate dents the deck or the fitting bends. Check your boat or hardware maker for the exact torque.

When the sealant is firm, run a fresh razor blade around the base and peel off the tape. Leave a thin, neat edge rather than a big fillet; thick exposed beads collect dirt and weather faster. For butyl, roll the extra squeeze-out up with your fingers or a plastic scraper.

After the full cure time on the label, repeat the hose test from step 1. Then put the headliner back. Log the date, the sealant used and photos in BoatMend so you know what is under each fitting next time.