Bedding Deck Hardware With Butyl Tape

Maine Sail

Member III
Over the years, especially in the last few spring weeks, via PM's/email, I have been asked how I bed deck hardware with butyl tape. I officially apologize for being so slow with completed photo examples. I have been meaning to do this but just did not have the time to complete it.

Late Sat night I was in the barn staring at a cleat, and a small scrap of clear thick Lexan, hmmmm......:rolleyes: A drill, counter sink, some butyl tape, my camera and a few minutes later I had the pics I needed. Sorry it took so long..

Here's how I bed with butyl.

Step 1 - Countersink the deck holes slightly and then clean everything with Acetone or a similar fast evaporating solvent.

Step 2
- Wrap Bolt Heads - You'll want to rip off a small piece of butyl and knead it into a string then wrap the underside of the bolt head.

Step 3
- Press the through bolts into deck hardware with some good pressure.

Step 4
- Strip some more butyl tape and make another round string. Wrap the string around the bolt threads or shoulder. Knead and work & twist the cones into the threads of the bolt and shape them like a cone.

Step 5
- Apply butyl tape to the rest of the base. It is perfectly ok to stretch and pull on the butyl while laying it on to make slightly thinner. I used 1/2" wide by 1/8" thick gray butyl tape for this.

Step 6
- In colder climates you may want to pre-heat the butyl to soften it some. After pre-heating with heat gun on the warm setting line up the bolts with the holes and press the hardware firmly onto the deck. For illustrative purposes clear polycarbonate was used in place of a deck (another MS first;) but don't worry one of the magazines will surely rip this idea off in no time...). This allows you to see what actually happens when you bed with butyl.

Step 7
- Install the backing plates, in this case I just used fender washers, and begin to tighten. You will be best to have two people or a good way to keep the bolt from moving. Ideally you do not want the machine screw or bolt to spin, but if you absolutely have to, you can slightly soften the butyl with a q-tip and some mineral spirits and go for it.

Tighten a little bit at a time as the butyl will ooze out slowly because the consistency is quite thick. Tighten, let sit, tighten, let sit etc. etc.. When little to none squishes & the bolt & nut become tight you can stop. If you have a wood deck core DO NOT crush it by over tightening, better yet bore out some core and pot the hole with thickened epoxy.

Here I have taken pictures of the underside and the top side of the fitting.

Underneath view when tight:

Deck side view:


Step 7
- Peel away excess ooze and clean with Meguiars cleaner wax, or a rag slightly dampened with mineral spirits. Do not saturate the rag with mineral spirits as it can creep under the fitting, just damp.

I find a ball of already "peeled" butyl works well at pulling away excess using a stab and pull motion. Stab the ball into the joint and pull away. The butyl will stick to the ball first and usually peel away from the joint. Alternatively you can use plastic razor blades or scrapers.

Contrary to popular myths about bedding all the butyl does not squeeze out from between the surfaces even after the fitting is fully tight. This is the magic of butyl, but it does take multiple small tightening events, ideally without letting the bolt spin, to get the vast majority of the butyl to squeeze out.

This is a view after tightening to full tight, and then removing the nut and washer. You can see how well it actually seals and also the o-ring seal of very thick butyl created by countersinking & butyl cone.

In short butyl is more labor intensive than a marine sealant but will last a very, very long time. Butyl never hardens, is significantly more flexible than any of the commercially available polysulfides or polyurethane sealants and the best part is that 30 years later it will come apart with ease. The only down side is more labor to install and it is not solvent resistant. Unless you regularly clean your decks with mineral spirits this is not a worry.

This is our 31 year old genoa track that was factory bedded with butyl, and is still bone dry 31 years later.

The butyl bedded chain plates also did not leak in 31 years.

If you decide to try this please take a look at Bed-It Tape..
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Sustaining Partner
Great timing! I'm about to install a new hatch in the salon cabin top just aft of the mast. I have some grey butyl tape on hand. Is there any particular method for hatches that differs from cleats, etc? The attaching screws are all blind into solid laminate so no leak issues there and also all outside the seal. Should be a simple matter of apply tape, install, tighten down, trim excess? Thanks, RT

wolly bugger

Member II
Maine sail, Thanks for all the info and all the detail.
When I bought my boat last years, I found a few leak at the bow and used pro seal 34 that I had at home. A couple week ago I remove the hardware that was seal with it. It look like a great product stretch like hell before the seal break (the label say 350%) stick to everything and is not so bad to clean, seal on contact and under water as well.
have you ever used it, and if so what do you think of it?
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Innocent Bystander
Can't say I've ever used or heard of Pro-Seal, which sounds a lot like an adhesive. Given that it comes in a tube, has to cure, and is designed to last "only" 15 years, could it really be easier to work with than butyl tape, which you can apply with your fingers? Probably not cheaper, either.


Member II
great pics!

Yes thank you for that, this was very informative, and good timing because we are about to rebed some deck hardware. Thanks!


Contributing Partner
Interesting stuff. But doesn't the butyl tape depend on pressure to maintain a seal? I mean, the stuff isn't really adhesive is it, the way polysulfide caulk would be?

Maine Sail

Member III
Interesting stuff. But doesn't the butyl tape depend on pressure to maintain a seal? I mean, the stuff isn't really adhesive is it, the way polysulfide caulk would be?

All sealants depend upon tight deck hardware to keep a seal. One of the many "myths" foisted upon us by the manufacturers, and some authors, is that you need an adhesive to make a seal. You need only a sealant to make a seal, it does not need 700 PSI of adhesion when mechanically fastened. CS Yachts is a testament to this. Nearly 80% of my vessel, at 31 years of age remains un-rebedded. Most of the stuff that was re-bedded did not even need to be and was more of a check/re-bed than a necessary re-bed. This was also all without any beveling that these boats remain very, very leak free. Add beveling and you'll likely never encounter another leak. Factory butyl bedding is and was very labor intensive and expensive process. That is why most builders did not do it..

Mechanically fastened hardware, with sufficient backing plates, and the proper fasteners, do not need an adhesive. All you need is some minimal adhesive properties to make the product stick to both surface well enough to accommodate any minor movement and stretching of the product. Butyl does this many times over and will also handle significantly more movement than most every marine sealant.

If your deck hardware moves more than this you have other significant issues...:egrin:



Contributing Partner
Looks great but should you not have some lock washers in there? Fender washers and plain nuts will work loose over time for sure. I hate nylocs myself but I always use some form of lock washer when bedding hardware like this.


Sustaining Partner
Ted, the point here is to demonstrate how Butyl works when bedding HW. No locking mechanism necessary for this demonstration.

Another huge plus of Butyl is that you can do this work in the cold as long as you pre-heat the tape to soften it.


Contributing Partner
I guess I am confused then. Are you saying that for demonstration purposes you would not bother with lock washer or lock nuts. Or are you saying that if you bed hardware using butyl you dont need to use lock washers or lock nuts period?

Maine Sail

Member III
I guess I am confused then. Are you saying that for demonstration purposes you would not bother with lock washer or lock nuts. Or are you saying that if you bed hardware using butyl you dont need to use lock washers or lock nuts period?


It was a demonstration. I used what I had in the barn but did want to spread the load some on the Lexan, so used some fender washers.

In the real world I generally use nylocs or splits and large backing plates...

P.S. Most boats are not made of clear Lexan either...:egrin:
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Sustaining Partner
Replaced the salon hatch two days ago, bedded in Butyl. Washed the boat today and hammered the new hatch with the hose. No leaks! I like that stuff! Way, way cleaner and easier to work with than "liquid" sealant/adhesives too. RT

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Sealant Happiness

Winter project season is here again....
Being about to tackle a re-bed of my mast deck-collar, this seems like a good time to 'bump' this great thread.

And also give a shout-out to Maine Sail !
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