Bedding Deck Hardware: Silicone vs. Butyl Tape

When installing hardware on the deck of your boat or when you’re adding new portholes, hatches or windows, it’s important to properly bed the hardware to ensure that water can’t get into your screw and bolt holes and cause rot and other problems. Bedding is the process that seals water out of the hole in your deck by using a silicone or rubber sealant. Today we’re going to compare and contrast the two most popular sealant options; marine silicone and butyl tape.

Marine Silicone

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Marine silicone, like our 3M Marine Mildew Resistant Silicone, is a readily available bedding and sealant compound. It is clear in color, works on fiberglass, wood, metal rubber and vinyl surfaces and cures in 24 hours. Silicone is great for use as a galley and head sealant, gasket adhesive, or bedding compound for portholes, hatches, windows, and marine hardware. Silicone seals and waterproofs while remaining flexible and is especially great for Plexiglass or Lexan surfaces.

Silicone does have a few drawbacks that you’ll want to consider. Many sailors find silicone messy and difficult to clean off your boat. To make matters worse, your boat’s gelcoat is prone to absorb leftover silicone that squeezes out from under the hardware and then the silicone attracts dirt. To prevent this, the best way to clean up the silicone is to wet sand it off, rinsing your sandpaper frequently to prevent grinding the silicone deeper into the gelcoat. If your hardware ever needs to be changed out, you’ll need to completely remove all of the old silicone before re-bedding, which can be a lot of work.

Silicone has a mediocre shelf life. Once a tube has been opened it will last for a year or two before drying out. A 3 oz. tube of marine silicone is comparable in cost to a 45-foot long roll of butyl tape.

Butyl Tape

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Butyl Tape is a non-hardening, elastic rubber that is great for bedding applications on boats. It can be used to waterproofing holes made for bimini and dodger frame fittings, snaps, awning track installation, stanchions and much more. Butyl tape is a soft, malleable material that can be easily trimmed, pressed and formed to create a water and airtight seal. It also increases adhesion with age after it’s applied, so it creates a long-lasting seal. Go ahead and really tighten your screws; you won’t squeeze out all the butyl no matter how hard you tighten the fittings.

Butyl tape is easily removed from hard surfaces without damaging the surface, even after years in the application and the same roll of butyl tape will last for years and years on the shelf.

Butyl tape also has some drawbacks and applications where it shouldn’t be used. Butyl tape will get hard in cold weather and will need to be warmed with a hair dryer if it’s below freezing before applying. Most importantly, Butyl tape can be broken down with mineral spirits, so it should not be used to bed fuel fills or vents as the fuel can damage the butyl and the seal.

Conclusions

We recommend using butyl tape for bedding deck hardware due to its ease of use and cleanup, longevity (both in an application and on the shelf) and affordability. However, there are applications where marine silicone is preferable like bedding portholes, bedding on plastics, or for other areas where butyl is not recommended. Additionally, marine silicone can be painted over, which may be a plus for you. Ultimately, it’s a choice of what you’re comfortable working with and what compound will best suit your application.

You can find both marine silicone and butyl tape at Sailrite.com.

Which is your preference for bedding deck hardware? Have you had positive or negative experiences with silicone and butyl tape? Share your thoughts in the comments!

8 comments
  1. James Macallister said:

    Another good choice is Sugru. Easily to use, no mess and provides a perfect waterproof seal.

  2. The Old Git said:

    Well, I used silicone to bed and seal the fuel depth gauge on a stainless steel fuel tank to my regret.
    The tightening of the screws obviously allowed the silicone to squeeze into the tank and this then was sucked into the carb (don’t ask how because there was a filter at the bottom of the fuel intake tube) and I was in a power boat race at the time that obviously cost me the race.
    Definitely not recommended for that application.

  3. Eric L. Baxter said:

    Sailrite is not going to want to hear this but there is absolutely no advantage in using marine silicone over the much cheaper hardware store household 100% silicone. No choice will work if you do not countersink the holes before bedding the hardware. I have crossed the Atlantic twice with all household silicone bedded fittings with zero water intrusion/leaks. It is also critical to coat all holes with epoxy as an insurance measure should water get by the silicone gasket that the countersink ceates beneath the fitting.

    • mitchell tanenbaum said:

      I’m replying solely from memory, and I’m not an expert, but I think marine versions of silicone have less or no ammonia, which may react adversely with polyester resin, and also may have anti-mildew additives. I have used marine silicone in my home as well as my boat with good results.

      • Eric L. Baxter said:

        There is no problem with epoxy; the silicone can with some effort, be scraped off of linear polyurethane paints. I admit I was thinking of my application- wood epoxy boats that I build and paint. Nothing beats household silicone above the waterline. I have no interest in having to retighten a butyl beddex fitting until the cows come home and dealing with the dirt attracting mess around the edges.

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