An Ode To Butyl Rubber

I like to think I’m pretty handy around the boat. Yank an engine and replace the motor mounts? Done it. Knock out a bulkhead and build a new one to replace it? Not a problem. Pull the shaft, install a new shaft seal, and lap the prop? Piece of cake. Install all new electronics and successfully network them together? Got that T shirt. I almost always leave things I work on in better shape than they were before I started, which is the true measure of success for any boat project. But there is one task for which I have virtually no talent. A chore I truly dread tackling. An important maintenance skill which I am hopelessly inept at.

I cannot use a caulking gun to save my life.

Oh sure, I can squeeze the trigger and make the stuff ooze out of the tube. But when I pull the nozzle along the surface where I want to lay a bead, the caulk drags and balls up. When I push the nozzle along the surface, thinking the tip of the tube will feather the flowing caulk, it builds up like a freshly plowed furrow. I attempt to use a moistened finger to smooth the bead, and it gets all over my hands. And then the caulking gun. And then everything around me. By the time I’m done, I have a stalactite of caulk hanging from my nose where I absentmindedly pushed my glasses back onto my face, my shirt is a total loss, because you just can’t wash the stuff out of clothing, and I’ve used a least a quart of alcohol and a half a roll of paper towels trying to get the stuff off everything it’s not supposed to be on.

I’ve made peace with my shortcoming. It’s one I can live with. I was resigned to having to allow an hour for cleanup after any five minute caulking job. But then I met my saviour. It is a miracle of modern science called butyl rubber. And since I discovered it, I have left my caulking gun behind and have never looked back.

One of the projects on our to-do list was to replace two hatches just forward of our mast. They both dripped from the hinges a bit when it rained, and the frame on the port one was warped just enough that you could see daylight past the seal, which means it leaked in anything more than a light drizzle. Having to put bowls under the hatches to catch drips whenever it rains just felt too much like living in a shanty for our taste. We considered trying to repair them in place, but I really wanted to replace them with heavier models. Hunter Marine used Lewmar Low Profile hatches, which are pretty light duty for hatches that tend to get walked on a lot since they’re so close to the mast (not by us but by every rigger and canvas guy that steps onboard. They just don’t seem to care). As part of our big Defender order during this year’s Annual Warehouse Sale, we bought two new Medium Profile hatches to replace the leaky ones. They have 1/2″ thick acrylic lenses instead of the 5/16″ acrylic on the old ones, and will stand up much better to abuse.

Normally, installing a new hatch would mean the use of caulk. Lots and lots of caulk. Some Boatlife or polysulfide, or the dreaded silicon, or God forbid maybe even some 3M 4200. I have no sympathy for anyone foolish enough to reach for a tube of 3M 5200. They get what they deserve because they brought it on themselves. There’s a reason they call it Satan’s Glue.

Anyway, the weather called for several days of dry, which was perfect hatch replacing weather. So, out came the old hatches.

Old Ones Out, New Ones Staged For Installation

Old Ones Out, New Ones Staged For Installation

Now I’ll be honest here. I’m a handy guy, but I value my time. While I cut the old caulk from below with my oscillating saw and removed the mounting screws to help the process along, I called our friends at Troendle Marine to yank the old hatches. They sent one of their crack marine mechanics over, who had them both out in under an hour. Money well spent in my opinion, as I would have sweated and cursed my way through the job for an entire afternoon, and let’s face it, I had blog posts to write.

So after scraping off all the old caulk and cleaning up the holes to accept the new hatches, I dropped them in place for a test fit. Even though they were the same brand (Lewmar) and size (size 40) as the old ones, the mounting holes were in different locations (naturally. This is a boat job we’re talking about after all). So I shot some epoxy into the old holes and a little more into a low spot where Hunter hadn’t faired out the surface properly at the factory, and waited for it to cure.

Interestingly enough, the easiest way to do this was with a tube of West Marine Six10 self-mixing epoxy adhesive, which is actually applied with, yes, a caulking gun. But since it is epoxy and not caulk, it is not inherently evil, and thus easy to use and achieve good results.


Easy And Useful


Difficult And Evil

See the difference? I mean, it’s so obvious, right?

So while waiting for the epoxy to set up, I started preparing the new hatches. The butyl rubber I use comes in a 1/2″ by 50 foot roll. It’s sort of like a long gray ribbon of chewing gum.

Hatches10 Hatches11So I layed a nice bead of it all the way around the hatch flanges, working it up into a slight mound as I went.


One of butyl’s many outstanding features is that it never hardens. It has the consistency of well-chewed gum today, and it will have the consistency of well-chewed gum 20 years from now. So unlike caulk, once you get started, it’s no problem if you want to take a break. Go ahead, make a sandwich, get some iced tea, it will still be nice and gummy when you get back. Phone’s ringing? Answer it. This stuff isn’t going anywhere. It’s not going to harden in your absence.

When I was finished gumming up the hatch flanges, my fingers were clean, my shirt was clean, my nose was clean, and there were no silicon skid marks all over the deck from accidentally tracking caulk around. It took 15 or 20 minutes a hatch to build up the butyl the way I wanted, rather that 5 minutes or so to coat it in a thick goop of caulk, but I was way, way ahead on cleanup time, so I’m fine with it.

I had already drilled the new mounting holes and had used my bevel bit on them (more on this in a moment). So I pushed each hatch into place and installed the mounting screws, working my way around the frame, tightening each screw in turn. After a few minutes, I gave them each another partial turn. At that point it looked like this:

Hatches5A nice bead of butyl rubber had squeezed out from under the hatch flange. Trace around the flange with a sharp knife, use your fingers to peel off the extra butyl, and done!. Nothing left but to stand back and admire your work.

Well, not quite. I wanted to finish the entire job while I was up there in the hot sun. Our boat’s original owner had had some nice sunbrella hatch covers made. Unfortunately, he mounted them with button snaps screwed to the deck, which has got to be the worst way possible to do such a thing.

Really, Really, Really Bad Idea

Really, Really, Really Bad Idea

Why a bad idea? Well, most decks have a plywood or balsa core sandwiched between an upper and lower layer of fiberglass. The plywood or balsa is there to give the deck stiffness. Fiberglass alone would result in the deck being something like a swimming pool springboard. Drill lots and lots of tiny holes in the deck and fail to seal them properly, and it gives water a way to leak into the plywood core. Which will then turn to mush. And then your deck is a bounce house in the sun. Oh, and if you do it this way, you also can’ t open the hatch when the cover is snapped down. There are probably some other reasons as well, but those will suffice to qualify it as a bad idea.

I had a sneaking suspicion those button snaps weren’t sealed properly. I removed one to check. Damn I hate being right all the time. But you can hardly ever be wrong if you just assume the last guy didn’t take the time to do it right. Whoever had installed those snaps (I’m going with the canvas guy who made the hatch covers) hadn’t bothered to put so much as a drop of silicon under them. They needed to be sealed. Fortunately, I just happened to have a nice golf ball-sized glob of butyl rubber made up of the excess that oozed out of the hatch flanges. So I took my bevel bit in my cordless drill and beveled each of the holes.

hatches7It only took a few seconds per hole, but hey, time is money, so I guess it’s too much to have expected whoever installed these to take the time orginally. I had beveled the screw holes for the new hatches the same way. By doing this, the butyl rubber compacts down into a nice tight gasket when you tighten the fastener.

So I then tore off small gobs of butyl from my ball of leftovers and stuck it in the holes. Remember, it’s not caulk. It’s uber bedding. It’s still nice and gummy and ready to go to work.


Screw the button snaps back down, and it compresses the butyl into a nice tight seal, with the excess squeezing out around the snaps.

Hatches9You don’t even bother scoring this with a knife. Just pinch the excess with your fingernails and peel it off. The butyl that got compressed into the beveled hole isn’t coming out.

Throw the leftover roll of butyl rubber in a ziplock and toss it in a locker, and it will be there waiting for you whenever you again need to bed a hatch, port or fitting. And if you screw it up and it leaks, it’s no big deal to just pop the hatch or fitting back out, add some additional butyl, and try again. It never cures. so you don’t have to scrape off the old stuff in order to add new, unless it’s gotten contaminated by dirt or grime. Have a few bits stuck in the non-skid that you can’t get off? Take a small ball of butyl and use it like silly putty to pull up the loose bits. Or a dab of mineral spirits on a rag will take it right off.

So if you’re saying to yourself, “Thanks Robert, I hate caulk even more than you and that stuff looks amazing, tell me more and where do I get some?” then here’s a link where you can learn more about this modern day miracle and purchase some for yourself:

So do yourself a favor and just say no to caulk. You won’t regret it, I promise!


5 thoughts on “An Ode To Butyl Rubber

  1. Paul

    I don’t know if it would work on every project, but I will never caulk again without this $5.00 tool:
    (the one on the left). After you apply the caulk, you use the tip of this tool to form the filllet. It leave a perfect fillet. If you get too much caulk, it builds up on the leading edge of the tool and you have to wipe it off with a paper towel but it really makes a great bead. I’ve not yet used one on a boat job, but plenty around the house. If you have to use caulk at some point, try one.

    I’d not heard of butyl rubber but I’ll give that a try when the application fits.

    1. Robert Post author

      That was my point in posting this. Butyl is great stuff for bedding things on a boat. More people need to know about it.

  2. jemiller22

    I LOVE Butyl Tape! I use it everywhere! I just rebedded a port with it. It took me about 3 hours to get the Port out and then scrape, scrub and scrub some more to get off all the 4200 and clear silicone caulk that had been used, then only about 30 minutes to put the Butyl Tape on, then secure the Port…. when it squeezes out you are golden! EASY cleanup too… Bonus! I also use Butyl Tape for non-conventional purposes as well! Check out my blog to see…

  3. Pingback: Finding an alternative to caulk - epoxycraft

  4. alan malnak

    There are a couple downsides, which makes it not always the best choice. Working with it can be messy, and cleaning it from surrounding areas, particularly fabric is tough. But the real reason it’s not a good choice is heat. Get the hot sun beating on the location you used the butyl and it’s a gooey mess, and unless the pieces are held by screws, bolts clamps whatever, your pieces will come apart, or give under pressure.Instead, use a sealant that cures, and holds under the heat of the sun.


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