Rebedding Deck Hardware

By Mark Corke

A leaking deck fitting can cause damage to deck cores and boat interiors. Rebedding may be all that's needed.

Photo of wiping hardware with solvent

Cleats, deck fills, lights, handrails, and antenna mounts are just a few of the many deck fittings that you find on the average powerboat or sailboat. All of these fittings usually require holes to be drilled for attachment. And all of these fittings are usually bedded into some sort of compound when a boat is built. Over time, age, sunlight, water, and general wear and tear take their toll, and when the bedding starts to break down, it allows water to find it's way below or, worse, into deck-coring materials.

If you suspect that a fitting is leaking, smearing a bit of goo around the outside and hoping for the best won't cut it. You've got to bite the bullet, remove the fitting, and start fresh. Removing old bolts and screws that may have corroded is often the worst part of the job, but it has to be done. Having a helper to hold the bolt while you unscrew the nut from below will make the job go quicker, and having a little moral support won't hurt, either.

To Remove A Cleat

  • Photo of removing screws from fitting
    Photo of rprying fitting up with putty knife

1. Some smaller fittings may be held in place with screws, in which case you shouldn't need to get to the underside of the deck. When the bolts or screws have been removed, the fitting should come away from the deck.

2. Pry it up with a putty knife or other thin blade if you need to, but be careful not to damage the deck. At this point, you'll be thankful if the original installer used the correct bedding compound. If an adhesive sealant such as 5200 was used, getting the fitting up can take longer. Don't rush if the fitting doesn't pop off right away; work a blade carefully underneath to separate it from the deck.

  • Photo of cleaning off old compound
    Photo of removing contaminates with acetone

3. Clean all traces of the old compound from the mating surfaces on the underside of the fitting and the deck.

4. Wipe with a solvent such as acetone to remove grease or other contaminants.

Apply a generous but not excessive amount of the chosen bedding compound to the underside of the fitting. Don't just squirt a bead around the perimeter; cover the whole base.

Place the fitting in position, insert the screws or bolts, and tighten evenly. Use new fastenings if the old ones are corroded, the heads are chewed up, or they're suspect in any way.

If you applied the correct amount of compound, some should squeeze out all around the base, a good sign. Clean it by scraping up as much excess as possible before finally wiping with the solvent recommended by the manufacturer.

Bedding Compounds

Marine stores may present you with a bewildering array of mastic and sealants; knowing which one to choose can be a problem. Basically, the most common products are either polyurethane or a polysulfide, both of which are excellent — but only if used for their intended purpose.

Polyurethane is an adhesive compound; 3M 5200 is perhaps the product that's best known. It shouldn't be used when there's a chance that you'll need to dismantle the joint later. Many manufacturers use 5200 for hull-to-deck joints, and for this kind of application, it's perfect. Polyurethanes also hold up well underwater and bond to most materials, but they can attack some plastics. They don't harm Marelon, so it's OK to use for bedding underwater fittings made of this material in plastic.

To Rebed A Cleat

  • Photo of applying sealant
    Photo of screwing hardware back in place
  • 1. Apply sealant. Spread out to a uniform thickness.

    2. Screw the cleat back into place.

    3. Scrape up excess sealant, then peel off the tape before finally wiping any last traces with the recommended solvent.

    Photo of scraping off excess sealant
     

Polysulfides, such as Boatlife products, remain permanently flexible, and these are my preferred choice for most jobs. They can be used above and below the waterline, and the joint can be separated later if that's necessary. Polysulfides are available in a variety of colors. I've found that the brown is a good match for teak and mahogany, but for the best seal with such oily woods as teak, use the recommended primer first. Polysulfides shouldn't be used for bonding such polycarbonates as Lexan or PVC because they'll attack them. Most window frames and other components containing plastic, therefore, are best bonded with a silicone product.

Another method I favor is the use of butyl tape for bedding. Popular many years ago, this practice waned when polyurethanes arrived on the scene. Butyl tape never sets and remains flexible forever, cleanup is easy, and because it comes on a roll, you just use as much as you need. In many cases, it's more economical than the stuff in a tube. But butyl isn't the right choice for every application. While it works well under cleats and stanchions held in place with bolts, it's less suitable under screws. The tightening motion of the screw tends to drag at the butyl and makes it pill up under the screw and be dragged from the fitting. Butyl works well with bolts in situations in which they can be prevented from turning and are secured from beneath with a nut. The one caveat is that not all butyl tape is created equal; be careful to use tape that's recommended for marine use.

Slightly more old school is Dolfinite bedding compound, which can be hard to find; I like it for bedding wood to wood. It can also be used for hardware-bedding applications. It has a strong aroma; every time I pop the lid, it reminds me of old boatyards. Dolfinite remains flexible for years, won't dry out, and won't destroy the parts if you ever need to break the bond later. It lasts for years, as a partially used tin can be resealed with no ill effects. It's available in white, gray, and brown.

Masking Tip

Here's a way to save time and make cleanup a snap. With the fitting sitting over the fixing holes, draw a pencil line around its base, then remove the fitting and put to one side. Stick down masking tape so it covers the pencil marks. Replace the fitting in the correct location, then cut around the base with a sharp knife or razor blade, remove the fitting, and peel up the tape on the inside of the cut line. When you bed the fitting down, any excess bedding compound will squeeze out onto the tape and will be removed when you peel up the tape. This method is faster in the long run and produces very little mess. 

— Published: Fall 2015


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