Install Boat Deck Fittings

By Don Casey
Published: April/May 2013

Once you've picked the appropriate sealant, success depends upon paying close attention to the details.

There was a time when re-bedding a cleat meant stopping in at the chandlery for some marine sealant, unbolting the fitting, squeezing some goo in all the right places, and tightening the bolts. Presto, no more leak! But much has changed. We have more sealants to choose from, and you have to pick the right one if you hope to keep that fitting watertight and still be able to remove it if necessary. Most middle-aged and newer fiberglass boats are constructed with a core of lightweight material between two fiberglass skins. If you don't take care to seal that core, water can get into it and cause core failure and, eventually, delamination. Doing it right isn't difficult; it just takes a bit of knowledge, thought, and attention. Here's how to go about it.

Set The Stage

A good bond begins with clean, wax-free surfaces. Use solvent to remove fabricating or preserving oils from new hardware. Clean away dust created by drilling. Use a wax-removing solvent (xylene, toluene, or acetone) to clean the fiberglass. Solvent-wipe the barrels of the bolts you'll be using.

Figure 1
All illustrations: ©2013 Mirto Art Studio,

Start by cleaning all the sealant off the cleat.

If you're re-bedding, hopefully the old sealant is one that will allow you to separate the joint without difficulty or damage. With the hardware loose, remove all traces of old sealant from it and the boat, typically by peeling it with a razor scraper or a chisel (Figure 1) followed by a solvent wipe. Where you fail to remove old sealant, the new sealant will attach to it, not to the boat. That makes the new seal the same as the old one and your effort wasted.

If the old sealant was silicone, it will leave behind a stubborn residue. Xylene (xylol) is the best solvent for dissolving silicone, but wiping with a xylene-saturated rag just spreads the contamination. Instead, wet the surface with xylene, then blot-wipe it using a single, short sweeping motion with a clean paper towel. Use each paper towel only once, and use as many paper towels as necessary. Test for silicone or wax contamination by misting the surface with water. If it sheets away, the surface is clean. If it beads, the surface requires additional cleaning.

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Tech Support

Degree Of Difficulty
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Tools and Materials:
  • Screwdrivers
  • Wrenches
  • Blade scraper
  • Wire brush
  • Power drill and bits
  • Core removal tool
  • Countersink bit
  • Caulking gun
  • Epoxy syringe
  • Solvent
  • Paper towel and/or rags
  • Epoxy
  • Silica or fiber epoxy filler
  • Masking tape
  • Sealant