Best caulking for roof seams?

[Detached Dad]

 I need to seal the seams on the roof. What's the best caulking for this?

[Rickf1985]

Urethane caulk but if there was any silicone there in the past it needs to be completely removed, residue and all. Nothing, including silicone, will adhere to old silicone. Silicone is for windows and bath tubs in houses and never for RV's!
Hopefully Terry will chime in here since he is very well versed on the use of caulk.

[TerryH]

As Rick wrote, if there is ANY existing silicone on the seam it has to be completely removed. Silicone contains silicon as does glass, hence the superb seal between glass and silicone. It is the worse possible choice for a seal between dissimilar substrates that are exposed to the elements. As per Rick it will NOT adhere to old silicone.

Here goes, my opinion based upon my experience.
First, read this - not entirely accurate, but close:
http://www.finehomebuilding.com/2004/05/01/making-sense-of-caulks-a...
What I do not agree with is Polyurethane:
It is no more dangerous to you than any other sealant you may use. Standard precautions, yes.
Stringy - depends entirely on the product and intended use. Some, such as those used for major joints such as tilt up buildings actually have that built into the manufacture for adhesion and cohesion.
As for butyl caulk, yes it is very water resistant and extremely viable - provided (which is not stated) - it is shielded from constant UV exposure. It is EXTREMELY messy to apply.

Butyl caulking: It does not really 'skin' as do others. It also should not be exposed to sunlight. The most common use for it is in residential and commercial glazing systems to seal butt joints in the butyl tape and corner blocks in curtain wall systems. In both cases the caulking is completely covered by finishing components. It also used to be used in vehicles that used rubber gaskets to install windshields, etc. Again, completely covered.
Gutter Seal: I've never used it. There are many varieties and manufacturers. GE for instance offers a Gutter and Flashing seal that is silicone, which you want to avoid. It would depend entirely on the product and composition you used.
General: Personally, I would avoid any inexpensive caulking that does not tell you it's composition. There are a lot of them in the big box stores.
No offence intended to those involved, but advice you receive from an associate at a big box store or local hardware store is difficult to accept as expert. My advice for future would be to look for a sealant supplier in your area and talk to them. They will likely be wholesale only, but if you pick a time when they are not busy they should be willing to suggest products. They also can direct you to a retailer for the appropriate product. I'll send a link to one in my area after this post so you have an idea of what I mean.

. Two suppliers of polyurethane I would recommend are Sika and NP-1.
Another member here, WrigleysBraveWin, suggested the following product. I have yet to try it, but from what I have read it sounds good.
ChemLink M-1

https://www.chemlink.com/m-1


Here is a link to a sealant supplier. I am in Canada, so they won't do you much good, but the general idea may help you in the future. As you will see, they do not deal in BBQ's, light bulbs, fertilizer etc. Only products related to sealants.
https://www.cascadeaqua.com/

Should you wish assistance with the cleaning of existing and application of new feel free to ask. What I would request from you is a photo of an as-is seam with a pencil, Bik lighter, etc. included in the photo for size reference.

[WrigleysBraveWin]

M1 by Chemlink or try Tremco Vulkem 116 ..... Available at Home Cheapo and Lowe’s .... Home Depot under $7 .... My local Lowe’s under $5 ....

Don’t be fooled by the price, it’s a very nice professional caulk, Tremco make high end waterproofing products ....

Tip: Like Food, Caulk has expire dates .... Check dates before buying - Date should be less than six months old or don’t buy unless you are going to use right away

[WrigleysBraveWin]

Urethane caulk but if there was any silicone there in the past it needs to be completely removed, residue and all. Nothing, including silicone, will adhere to old silicone. Silicone is for windows and bath tubs in houses and never for RV's!
Hopefully Terry will chime in here since he is very well versed on the use of caulk.

As Rick points out be darn sure to clean and prep area, remove any Silicone as Silicone has a hard time even sticking to itself!

[WrigleysBraveWin]

I need to seal the seams on the roof. What’s the best caulking for this?

Seal Seams?

If there is much movement you may wanna use a tape verses a caulk .... By tape I mean something like Eternabond ..... If caulking, make sure you work caulk up/under any lip or void and push caulk into voids - DON’T PULL Caulk - Rather push caulk out of gun into seam .....

I’ve seen way too many use a caulk gun and they pull the caulk, don’t do that push caulk out of gun and into seam or joint and make sure you clean and prep area ....

Preparation is the entire meal, don’t skimp on prep!