Why Butyl vs Caulk under roof vent flange?

[H20ENG]

What is the primary advantage of butyl tape vs just using Dicor or similar caulk (not silicone) under roof vents, windows, trim etc? That bubble gum seems to never stop oozing. I'm not taking things apart every few years unless something is wrong. If it goes together correctly there is less chance of things going wrong, right? 🙂
I understand manufacturers use it because of its application speed. Is it really the best solution? Caulking with an appropriate sealant seems so much better, then the lap seal on top. Key word "appropriate", which is the gist of my question.
"Because that's what the manufacturers use" is not an acceptable answer to me unless I understand the WHY. Opinions count as its all collective information.
Thanks again all!

[Optimistic_Para]

H20ENG wrote:
Thanks everyone. Do you have a source that you like for the "good" butyl tape?

Try getting it from a marine source instead of an rv dealer. Boats are a way more demanding environment than rvs, I don't think a good marine source would sell the cheaper, less effective stuff.

INCOM Butyl Caulking Tape

[joshuajim]

When I had my metal building installed 13 years ago, they used butyl tape on the panel joints. They left a number of rolls and I still use them on my RV. They are still as good as the day they were first used 13 year ago.

[theoldwizard1]

mike-s wrote:
Butyl tape (not caulk) is a bedding compound, it's meant to be squished between things to seal them.
.
.
.
You bed a roof vent in butyl tape, screw it down, wait a day or two for it to squish out the edges, remove what comes out, then cover the seams and screws with lap sealant.

Butyl tape is probably the BEST sealant you can use, assume the device has an adequate mating flange and fasteners. This is all that experienced sailor use for their port lights (windows). It stays soft for many years.

2 things with butyl tape. Don't over tighten the mounting flange and press out all of the tape. What does squeeze out can be cleaned of waded up, stored in an air tight container and REUSE !

[mike-s]

Amazon sells the Dicor butyl tape. It's fine, but not as sticky as some others. I can't point to a good name, I usually just go to the RV dealer and examine what they have on the shelf, if it's stretchy (taffy stretchy, not rubber band stretchy) and sticky, it's good. A roll lasts a long time unless you're doing everything. Butyl tape will have a smooth surface coming off the roll, putty tape is usually rougher.

[ScottG]

Everything on my roof is just caulked down. No "bubble gum" (Like!) tape anywhere.
It made it easy to rework a couple of things.
I would not ever use gum again.

[H20ENG]

Thanks everyone. Do you have a source that you like for the "good" butyl tape?

[mobeewan]

Butyl tape is sticky and seals better than putty tape.

[D_E_Bishop]

I do not know if each tape Winnebago uses has a different composition but I do know the butyl tape they recomend for windows is pretty darn good. Winnebago does not recommend using silicone on the edges and the tape doesn't squeeze out.

The windows that were replaced due to leaks between the glass look terrible. I bought the tape Winnie uses and I'll be resealing the frames to the walls.

[mike-s]

enblethen is correct - caulk or lap sealant will end up gluing it down, making it difficult if not impossible to remove without damaging things in the future. It's hard enough removing lap sealant when it's just on the surface. DrewE is also correct - good quality butyl tape won't dry out in a long, long time. But beware, there's also putty tape which is sometimes sold as butyl tape, but isn't. It's more like plumbers putty in tape form. Butyl tape will stretch until it's very thin. Putty tape won't.

Butyl tape (not caulk) is a bedding compound, it's meant to be squished between things to seal them. Dicor is a company which makes many products, including both butyl tape and lap sealant. One can only assume you're talking about their lap sealant, which is popular around here. The name says it all - it's a lap sealant, it's meant to overlap a seam. And, it's self-leveling, so is not suitable for anything on the sidewalls, it will just run and make a mess.

You bed a roof vent in butyl tape, screw it down, wait a day or two for it to squish out the edges, remove what comes out, then cover the seams and screws with lap sealant. Similar for sidewall stuff, except you caulk the edges - I use Sikaflex 221, which I prefer to the Geocel Proflex often mentioned around here, for a number of reasons.

[Gjac]

Either will work for a roof vent but I would use the butyl tape. We did some testing of various ways of sealing airframes were I worked and all of our Blackhawk helicopters were sealed with butyl caulking between riveted skins. We also used this caulking to seal composite air frames. It is more flexible does not dry out or shrink like other materials. There is a lot of different loads put on these airframes in flight and things move, not on like a MH traveling on bumpy roads. I have seen 20 year old airframes come in for overhaul and repair and the butyl seams are still good in spite of rivets and Al skins being corroded. MH's do twist, and we have all heard of wind shields cracking when improperly leveled on some MH's, so that is why I think it is a good thing to use a flexible sealant like the Butyl tape.

[rhagfo]

I don’t put either under vent flanges. Dicore self leveling applied properly will seal flange.

[donn0128]

I dont think you would want to put butyl on rubber roof. In case the butyl tape has petro chemicals in the fromula you could be asking for trouble. On the roof I have always used a generous bead of Dicor, screw whatever down and more Dicor over the screw heads and around the edges.

[DrewE]

I think one reason is because it doesn't dry out and crack the way that many caulking materials do over time, but remains flexible and stretchable. It's also what the manufacturers of the roof vents, windows, etc. generally recommend for use, at least in the handful of installation instructions I've seen.

[H20ENG]

I've only ever dealt with the grey