Roof raise sealants

[Pigeoneer]

What are everyone's thoughts on sealants between skin seams in a roof raise?

Not just seam sealant at the edges, but directly on the overlap before riveting.

 

[fo4imtippin]

i use lexel for sealing things like my windows and roof deletes. It expands well, sticks well and can be applied on wet stuff. It cleans up alright with mineral spirits and drys clear. Will stick to itself if you do any repair work.


I use sikaflex or seam seal for UV stuff, but lexel is pretty awesome for a secondary barrier.

 

[musigenesis]

directly on the overlap before riveting.

This is the best way to seal two overlapping sheets because it mechanically squeezes the sealant between the two layers, closing the seam even if the adhesion of the sealant fails (it essentially creates a gasket). If you seam-seal after the riveting, you're relying entirely on the adhesive properties of the sealant to provide watertightness (and this may be adequate, it's just not the best possible).

That being said, I imagine that doing this for large sheets like what are used in a roof raise would be difficult to manage. I've only used the technique for riveting sheets that are small enough for me to apply the bead of sealant, place the piece with adequate clecos, and wet-rivet everything before the sealant hardens (like, a 24" x 24" patch over one of my exit hatch openings, for example). Even with pieces this small, I have to keep the sealant (I use Dynatron-550 as do many others) misted with mineral spirits to prevent it from skinning over too quickly.

 

[DeMac]

This is the best way to seal two overlapping sheets because it mechanically squeezes the sealant between the two layers, closing the seam even if the adhesion of the sealant fails (it essentially creates a gasket). If you seam-seal after the riveting, you're relying entirely on the adhesive properties of the sealant to provide watertightness (and this may be adequate, it's just not the best possible).

That being said, I imagine that doing this for large sheets like what are used in a roof raise would be difficult to manage. I've only used the technique for riveting sheets that are small enough for me to

apply the bead of sealant,

place the piece with adequate clecos,

and wet-rivet everything before the sealant hardens

(like, a 24" x 24" patch over one of my exit hatch openings, for example).

Even with pieces this small,

I have to keep the sealant
(I use Dynatron-550 as do many others)

misted with mineral spirits to prevent it from skinning over too quickly.

----------------
Pictures to aid your good words, Sir.

I learned most of what I photographed from Musigenesis & ECCB, anyway. I had the same terrific results on my Roof Patches, using their methods, too.

 

[Pigeoneer]

Thanks for all this, definitely going to follow it to a Tee for the flasher lights/emergency exit/misc repairs.

I guess a small vertical bead for the roof raise skin wouldn’t hurt, I was just concerned it would create oil canning.

 

[musigenesis]

Oil-canning will happen if the sheet metal is too thin to support some kind of pressure (like from expanding spray foam) pushing it outwards. It shouldn't make any difference whether there's a small bead of sealant under the seams.

 

[LargeMarge-TC]

2003, for our ExpeditionVehicle, we mounted the windows with Vulcum 116 adhesive.
.
Nearly two decades full-time live-aboard.
Our Vulcum 116 remains soft and pliable.
.
Would we use it again?
Yep.