Silicone is truly evil.

[ebb]

We certainly done a bunch of rantin-n-aravin about silicone here.
It has its place in the engine room.
There is a hybrid by BoatLife called LifeSeal which by other manufacturers is well thought of. It's not new, been around for 20 years. LifeSeal is a silicone/urethane mix. Supposed to have the best of each and none of the bad.

I've used it on the boat, but it is untested. Its ability to stay attached to surfaces and, most of all, to stay flexible for 20 years in the tropics I have yet to witness.
I check the forums every now and again but most can't yet make the distinction between LifeSeal hybrid and BoatLife LifeCaulk polysulfide. It is Boat Life's fault in keeping the confusion going.
Professionals use Bostick products who have customed the hybrid for specific uses. Like one hybrid for caulking teak and synthetic decks and another that resists squeezeout for bedding stanchion bases and portlights.
[Adding to the confusion is exampled by BoatLife selling a 'marine quality silicone sealant' under their own label. Doubt there are cautions about its use around a boat on the tube. I think this irresponsible. And is a major reason I steer away from their products.]
Would think that Sika and 3M have their versions.

So there is a 'silicone' product that could be used if you want to pay for it.

Imco most of our aps can't really use a wet caulk successfully. Bostick's hybrid silthane for mounting stuff has body built into it, forget the term they use. LifeSeal has only the one tube, I believe. If you don't have a thick hard-to-squeeze goop there's no gasket quality. If you got metal to fiberglass you going to leak even tho you put $5 of rubber there.


SO, butyl IS THE WAY TO GO.
If you use butyl tape you don't have a mess.
If you have a difficult surface you can augment with tube butyl. IT's very sticky, so I believe you can get as good a seal as with the adhesives: polysulfide and polyurethane. You are just not gluing your fitting in forever.
And maybe having it leak anyway.
You have to learn how to use butyl. If you have something like a portlight that always requires rebedding then use butyl bedding not adhesive. Most cruisers use butyl I believe for portlight frames. Haven't heard any grousing about it - but then most forums are not set up for follow-through on a subject.

Butyl will always stay soft (pliable) and sticky. Polysulfide can get hard and start cracking in a couple years, depends where you are located.
I don't doubt that butyl can give up the ghost but it's a piece of cake to take the fitting or whatever apart and rebed it. You know it's something you can do, not something you want to avoid.

That's my take on Butyl. The tape and tube are inexpensive. I'll bet their storage life is 10 times longer than tube polysulfide. Means we can have it in the bosun's locker, always available.


I have a Marelon seacock that's going in on 1/8" b.tape. I'll use tube b. on the thruhull flange and in the bolt holes. Underwater, I know, but if it leaks I can redo it OR clean it off with Stoddard solvent and zapp it with polysulfide.

I'll have lexan windows bolted on over butyl tape. It bends nicely around curves. I can see the method (simplified) as stick on the tape, locate the fastening holes, put the fixture in place, poke the fasteners thru with a bit of wet butyl. With a seethru material like lexan dry spots will be noticed. I'm thinking that a dry surface could be primed by pre-smearing wet butyl on it to help get 100% contact? That's an idea for now.