Best Seam Sealant for RV Longevity: Sikaflex, 3M, Proflex, or Alternatives?

[jocyt]

So I have been searching everywhere for what everyone says is the best seam sealant. There seems to be a lot of mixed reviews between sikaflex 221, 3M, and Proflex.

What do you guys find is best for longevity?

Any thoughts on Sikaflex 521 UV?

 

[AlphaHare]

I can't speak to longevity. That said, IMO it's specific use more than one size fits all.

I've been using Geocel lap sealant for sealing between flat panels riveted together. I think it's important to have a wetter lap sealant for good squeaze-out when riveting. I like it, but I don't have any mileage on it. Geocel Pro Flex RV sealant PRO FLEX® RV FLEXIBLE SEALANT - Geocelusa

3M 5200 is a beast, well known for bedding and caulking on boats. It's often called 'the devil's caulk', or, "what part of permanent did you not understand?" I stay away from it.

3M 4200 is probably comparable to Sikaflex 221. It can be removed with effort, but still makes a good seal. Both of these products are as much adhesive as sealant. I don't think I'd use them between flat panels of sheet metal.

And I'm going to be using a self-leveling sealant for roof penetrations.

I'm also sure you can totally overthink this. ;>)

 

[Mr P]

Currently* overthinking this.


*currently means day 3

 

[GunnyVP]

So I have been searching everywhere for what everyone says is the best seam sealant. There seems to be a lot of mixed reviews between sikaflex 221, 3M, and Proflex.

What do you guys find is best for longevity?

Any thoughts on Sikaflex 521 UV?

As an ex-body tech, I swear by 3M 08307 self-leveling epoxy seam sealer that comes in the auto-mix tube. It’s the gold standard for the auto body industry. Some auto paint stores will allow you to return the gun for 90 percent of the sale price if you keep it clean and in a resellable condition (clean gun, keep the bag and the box not torn up). It takes about two auto-mix tubes to do the roof of a 30-foot bus, including both sides of the ridge lines. I washed the roof with Dawn dish soap and rinsed it real well to clean and degrease it, and then I removed the old sealant from the seams, and I then wiped the seams with denatured alcohol. I then applied the 3M self-leveling epoxy seam sealer. It goes on clear and hardens as a milky white. The hotter the outside temperature, the quicker it hardens. 10 to 15 minutes is average set time on a warm day. It takes longer to set on cold days. I then put Dicor tape over the seams, burnished the tape, and then painted two coats of Dicor metal roof sealant over the tape.

I hope this helps!

 

[Mr. Beefy]

When you say 'seam sealant', is that what you're actually using it for? I've gone deep down the adhesive/sealant rabbit hole, and what I've learned is that - like any tool - there's a right tool for a particular job. The properties of the various products in this realm vary wildly, depending on the intended application.

 

[Mr P]

For discussion, during a roof raise what is the "best" way to seal/bond:

1. the top of a panel to the underside of the "drip rail"
2. a panel overlapping another panel, whether horizontal or vertical
3. panels to the hat channel?

I have a little auto body experience from WAY back. some seals sealed with a hard tar-ish material, others with a more gooey tar like material, others with a hard glue like bond.

 

[GunnyVP]

For discussion, during a roof raise what is the "best" way to seal/bond:

1. the top of a panel to the underside of the "drip rail"
2. a panel overlapping another panel, whether horizontal or vertical
3. panels to the hat channel?

I have a little auto body experience from WAY back. some seals sealed with a hard tar-ish material, others with a more gooey tar like material, others with a hard glue like bond.

A panel overlapping another panel is always best. To illustrate, a roofer always starts the first course of shingles at the lowest roof edge and then layers the next course of shingles over that.

Any time a butt join (two she’s butted end to end) or a drop-in of sheet metal into a channel are used without a weld (not a filled seam; an actual weld), then there is likelihood of water penetration.

Ensure overlap on the roof is always made front to back and sloped to the outside away from the top/centerline of the roof.

On the bus sides ensure the overlap is front to back and layered bottom to top.

The reason you want to do that is because as you drive in rain wind would drive water into and under the seam if it faces forward.

As you join the layers you can run a bedding bead of 3M 08307 epoxy self-leveling seam sealer or a bedding bead of 3M 5200 before you screw the panel down. Just remember that 5200 thick like a caulk and once it sets you’ll need to use a piano wire or non-wound guitar string to separate it.

After everything is done run a small bead of the seam sealer along the edge where the plates join and smooth it with a gloved finger. On a roof I’d do that and then apply Dicor tape over the seam. Then I’d paint the entire roof with two coats of Dicor metal roof paint.

Soft sealer used to be used on car/truck drip rails, but now everything is epoxy.

Good luck!

 

[mhreynolds]

I can't speak to longevity. That said, IMO it's specific use more than one size fits all.

I've been using Geocel lap sealant for sealing between flat panels riveted together. I think it's important to have a wetter lap sealant for good squeaze-out when riveting. I like it, but I don't have any mileage on it. Geocel Pro Flex RV sealant PRO FLEX® RV FLEXIBLE SEALANT - Geocelusa

3M 5200 is a beast, well known for bedding and caulking on boats. It's often called 'the devil's caulk', or, "what part of permanent did you not understand?" I stay away from it.

3M 4200 is probably comparable to Sikaflex 221. It can be removed with effort, but still makes a good seal. Both of these products are as much adhesive as sealant. I don't think I'd use them between flat panels of sheet metal.

And I'm going to be using a self-leveling sealant for roof penetrations.

I'm also sure you can totally overthink this. ;>)

"what part of permanent did you not understand" - actually, for several dollars per oz you can buy a 5200 "remover" which at least softens it up a bit. don't ask how i know this...

 

[Mr. Beefy]

"what part of permanent did you not understand" - actually, for several dollars per oz you can buy a 5200 "remover" which at least softens it up a bit. don't ask how i know this...

I used a lot of 3M 550FC in our build, until I couldn't find it anymore locally. Used to get it at a roofing supplier but they stopped carrying it. Loved the stuff, but you definitely didn't want to let it sit around for long. Lost about 1/2 my tubes from solidifying in storage. Learned the hard way that moisture-cured PU finds moisture even here in the AZ desert. Especially the FC. Everything I used it for I used in conjunction with fasteners, but I probably didn't have to. That stuff is s-t-r-o-n-g.

 

[nikitis]

For my roof raise sides, I stuffed the side panels under the window seal, and over the lower panels so it works like siding on a house does.

In the back I could not do this due to the nature of the windows/door and corners would not fit, and it's easier to just overlap up top. In this case, I did indeed just cap the top on the outside which is bad for rain, but I used a strip of butyl tape, which when pressed together and riveted flat, came out uneven on the edges. some pushed out above the edge, and other spots, had a little dip where water could potentially pool in between the panels.

In addition to butyl tape, I took at razor blade and cut all of the excess that squished out into the open so it's a clean edge, and then took a layer of caulking additionally and filled in the little pooled areas.

The end result was a clean look that was perfectly sealed. I let it rain for months and had zero leaks.

 

[Mr P]

I am using Loctite PL S30 "Roof and Flashing" , about $9 at Lowes. I'm using it at panel overlaps. Ask me in 20 years how it worked....

I have lapped mine in the rear, unlike Nikitis. It took a little more time, but I'm not dependent on my sealer since it's lapped.

 

[fo4imtippin]

"what part of permanent did you not understand" - actually, for several dollars per oz you can buy a 5200 "remover" which at least softens it up a bit. don't ask how i know this...

My brother-in-law used it to seal the outboard motor bracket bolts on his boat before he sold it to me. When i had to remove the motor to repair the steering cable, we chained the boat to a forklift, held the motor with a crane and a backhoe pulled the motor off. I thought i would end up with 2 separate sides of a boat, but eventually it popped.

 

[Mr. Beefy]

Just a general comment on anything silicone...

I have yet to encounter a situation where one of the multitude of moisture-cured polyurethane adhesive/sealants didn't do everything silicone does, and a whole lot more. About the only advantage I've found with silicone is it's more likely to still be useable (aka not a block in a tube) after extended periods storing post-opening. But that's not enough for me to use it. IMO moisture-cured PU is proof God wants us to be happy.

Case in point: In this moment I find myself having to remove and replace a couple cable glands on our bus roof (not due to leaks). When I installed them 5+ years ago I used 3M 540. After pulling them up and removing the bulk of the residue, there's still some left that would require herculian efforts to remove (which would likely include the underlying paint). Were this silicone - I would absolutely have to go through those herculian efforts - as nothing would stick to it if I didn't. With 3M 540? Get most of it off (easy with a plastic razor), smooth out what's left, and re-install using 540 again just like I did the first time. The PU that's still there will continue to stick to the substrate just as well as it ever did, and the new PU will stick (and seal) to it without issue. And if I paint over them the paint will stick to the PU as well.

 

[GunnyVP]

"what part of permanent did you not understand" - actually, for several dollars per oz you can buy a 5200 "remover" which at least softens it up a bit. don't ask how i know this...

I’ve found the best way to remove 5200 is a “garrote” made of guitar string. The residue can be scrubbed off or sanded off.

 

[Bjorkinman]

Ive used 5200 and dicor lap sealant. Id stick with 5200 for any points of entry, pun intended. I'm in the process of adding an entry point for Starlink, an oversight in my earlier build phase.

 

[Mr P]

Mr Beefy, a note on silicone, it is a paint repellent. It can spread well beyond where it is applied, in trace amounts, that will wreak havoc on the next coat of paint.

 

[jocyt]

I can't speak to longevity. That said, IMO it's specific use more than one size fits all.

I've been using Geocel lap sealant for sealing between flat panels riveted together. I think it's important to have a wetter lap sealant for good squeaze-out when riveting. I like it, but I don't have any mileage on it. Geocel Pro Flex RV sealant PRO FLEX® RV FLEXIBLE SEALANT - Geocelusa

3M 5200 is a beast, well known for bedding and caulking on boats. It's often called 'the devil's caulk', or, "what part of permanent did you not understand?" I stay away from it.

3M 4200 is probably comparable to Sikaflex 221. It can be removed with effort, but still makes a good seal. Both of these products are as much adhesive as sealant. I don't think I'd use them between flat panels of sheet metal.

And I'm going to be using a self-leveling sealant for roof penetrations.

I'm also sure you can totally overthink this. ;>)

Thank you so much! We are using Dicor for roof stuff (solar, hatches, ect.) just debating on panels from roof raise and things so this was very informative!

 

[jocyt]

As an ex-body tech, I swear by 3M 08307 self-leveling epoxy seam sealer that comes in the auto-mix tube. It’s the gold standard for the auto body industry. Some auto paint stores will allow you to return the gun for 90 percent of the sale price if you keep it clean and in a resellable condition (clean gun, keep the bag and the box not torn up). It takes about two auto-mix tubes to do the roof of a 30-foot bus, including both sides of the ridge lines. I washed the roof with Dawn dish soap and rinsed it real well to clean and degrease it, and then I removed the old sealant from the seams, and I then wiped the seams with denatured alcohol. I then applied the 3M self-leveling epoxy seam sealer. It goes on clear and hardens as a milky white. The hotter the outside temperature, the quicker it hardens. 10 to 15 minutes is average set time on a warm day. It takes longer to set on cold days. I then put Dicor tape over the seams, burnished the tape, and then painted two coats of Dicor metal roof sealant over the tape.

I hope this helps!

Didn’t even know this was an optionmy head is spinning with all the different choices. We’re definitely looking into this though.

 

[jocyt]

When you say 'seam sealant', is that what you're actually using it for? I've gone deep down the adhesive/sealant rabbit hole, and what I've learned is that - like any tool - there's a right tool for a particular job. The properties of the various products in this realm vary wildly, depending on the intended application.

that’s what we learned as well, it’s just a never ending cycle of a thousand right answers. We’re using it for outside seams (new from roof raise and resealing existing ones)

 

[jocyt]

Ive used 5200 and dicor lap sealant. Id stick with 5200 for any points of entry, pun intended. I'm in the process of adding an entry point for Starlink, an oversight in my earlier build phase.

Thank you!