Silicone or Polyurethane?

[kidharris]

Originally Posted by Chrise

Wow, thanks for your quick reply. I so enjoy hearing from passionate people about whatever, and it seems you have a passionate hate for silicone. Excellent! But why?And also you would go with Polyurethane, or something else?

Silicone does not stick unless it is operating room clean (peals off after it cures, however it can make compression gaskets) and nothing sticks to it (paint, coatings, etc)


Polyurethane is tough and sticky, however you don't have much finishing time to smooth it out, you need to do small areas and work fast.

[kidharris]

Originally Posted by john61ct

And yes the Henry products are silicone, excellent reputation for that final coating seal

Henrys makes other coatings as well as silicone

Originally Posted by john61ct

but I don't know how we don't hear about the usual horror stories, it must at least adhere to itself in subsequent applications years later

what makes you think that Henrys silicone formula will stick to itself?

[katix]

This is fabulous info; thanks y'all!!

[john61ct]

Originally Posted by kidharris

what makes you think that Henrys silicone formula will stick to itself?

Are you saying it doesn't?

All those RVers swearing by the product, never seen a mention of any such problem

[john61ct]

Originally Posted by katix

This is fascinating! Y'all have some great recommendations for sealing roof holes. Do these same products (3M 5200, 4200, Sika 295-UV...) work well for sealing windows?

That completely depends on what material the windows are made from

both sides, wherever the sealant / adhesive is touching.

Always read the data sheet

[Ronnie]

Originally Posted by john61ct

Are you saying it doesn't?

All those RVers swearing by the product, never seen a mention of any such problem

I have heard some horror stories about it peeling off, as well as recoating not working because of adhesion problems.

[LargeMargeInBaja]

Originally Posted by Timeline

There is always a better choice than silicone except maybe for building aquariums. I give tubes of the stuff to my worst enemies for their birthdays.

.
a -- My birthday is coming up...
.
.
b -- My go-to sealer is Vulcum 116.
For our ExpeditionVehicle, I mounted our windows with Vulcum 116 as a sealer... and unannounced adhesive.
On our rig, it is pliable and soft years later.
.
I was so impressed, I used Vulcum 116 to stick our photovoltaic conduit to our roof.
.
Get it in the right place the first time... removing our conduit would require three big-time 'professional' wrestlers or one sturdy farm-girl.
And would take most of the weekend.
.
.
Inside:
For your proposed roof-rack, I think I would run a length of stout sheet-metal under your ceiling for additional tear-resistance.
I would bolt through that with yuge fender worshers.
.
Outside:
I think I would install yuge rubber worshers between the external 'feet' and the roof.
I would probably cover everything with a couple-three layers of mobile-home roof tape.
I get rolls of 4" x 10' QuickRoof UltraBond at Jerry's, our local-owned home-improvement center.
.
.
Of course, my preference is a roof without holes.
Fans?
Coolers?
Observation deck access?
And my favorite -- sky-light over the bed?
[spit, spit, spit, spit-spit-spit]

[Timeline]

Originally Posted by LargeMargeInBaja

.
a -- My birthday is coming up...

And my favorite -- sky-light over the bed?
[spit, spit, spit, spit-spit-spit]

HAHAHA!



Hi Marge!

I like your attitude and you seem really nice so I'd be sending you some good old Vulcum 116. I did notice one person in this thread who would be getting a case of clear silicone though....

Have a great birthday!
John

[Chrise]

Nice details and pics. I really need to contribute more. I am using the big Unistrut and components and Grade 5 hardware where I can. I consider my "rack" just a foundation as I am not certain what panels I will be using, or how I will attach them. For now getting the attachments and anything else through the roof before I spray foam is the goal. It went well. I used the 3m sealant on the rack bolts and in places around the roof hatches I built. We've had some showers of late and no leakage! Cheers! Chris

Cheers

[Zork]

The very best sealant I have ever used is Pro-Seal 890 Class B fuel tank sealant. P/S 890 Class B is a two-part, manganese dioxide cured polysulfide compound. This stuff has been used since the 1950's when it was developed to seal Super Constellation aircraft fuel tanks.

It's designed to hold up to just about any chemical, including jet fuel and gasoline. It's even used to build homebuilt aircraft -- the Bede BD-5 Microjet that was made famous in the movie Octopussy with Roger Moore as Bond is put together with pop rivets and this sealant, and it lasts forever because it never quite cures into a hard solid. Some people say that the only reason you need the rivets is to keep it in place while the sealant cures.

It is not cheap, but it beats just about everything out there. If you want to remove it, you use a pro heat gun, but you have to get it really hot before it gets gooey again.

And from personal experience, ALWAYS wear disposable surgical gloves when working with it, otherwise you'll have to wait WEEKS for the stains to fade off your skin and nails.

https://www.aircraftspruce.com/catal...clickkey=15700

[nautilus]

I AM SO GLAD I READ THIS! I was going to use silicone to seal the windows. When I removed the windows they were only held in by screws and the only 'sealant' was this straight rubber gasket type of material hiding the top screws that the window closed into. But do you guys know what kind of rubber this is and where I can find a replacement (picture below)?

Another question, when you guys sealed the window did you use sealant all around the window frame? Because that was our plan and that would render our windows pretty permanent, does anyone see an issue with that?

Sorry in advance for the novice questions.

[kidharris]

Originally Posted by nautilus

I AM SO GLAD I READ THIS! I was going to use silicone to seal the windows. When I removed the windows they were only held in by screws and the only 'sealant' was this straight rubber gasket type of material hiding the top screws that the window closed into. But do you guys know what kind of rubber this is and where I can find a replacement (picture below)?

Another question, when you guys sealed the window did you use sealant all around the window frame? Because that was our plan and that would render our windows pretty permanent, does anyone see an issue with that?

Sorry in advance for the novice questions.

I could not determine much from the pictures, but ....


I would not use sealant on anything that did not come from the factory with sealant or anything that I might have to replace. I did roofing and waterproofing for a living for many years and I have seen so many people make leaks worse by "sealing" with out a proper understanding of how the waterproofing/weatherproofing "system" is supposed to work.

With the exception of some car windshields, some skyscraper windows, and custom plate glass windows, most of the window systems use a combination of flashing - shingling of the various components so that the higher ones overlap the lower components or in the case of wind driven water/rain the up wind components overlap the downwind components. Some boat windows need to be waterproof, most other windows need to be weatherproof. IMHO, caulk/sealant should be a last resort, not a substitute for good design.

Compression gaskets (compressed by the screws/bolts attaching the component) allow for removal and re-installation and some window sills have tiny drainage gutters (possibly with weep holes) to drain any infiltrated or condensed water back out of the system.

Caulk/sealant in the wrong place can form a dam and block the drainage and make the window leak into the wall or make removal difficult/impossible without damage.

My advice would be to figure out how all of the design was supposed to work and look for any weakness. A good time to do this is before you close the wall up and you can no longer easily see small leaks. Condensation problems are a different story, but the built in drain gutters in many window designs will also deal with it also, if you don't block the drainage with your sealant.

I have seen many mistakes made by amateurs, pros, and even crappy engineering.



Testing:

Remember that water flows down hill (start at the top) unless driven by wind or capillary action. To see details start testing with a spray bottle or bug sprayer filled with water, use some food coloring if necessary but test for staining? (different colors can help you differentiate between where you sprayed - where the water came from), spray from all angles, and watch the water drainage and then make your decision on what to do before sealing. Rinse, dry, repeat.

A hose can also be used to test for leaks, but if I did not understand the system I would do a flow/drain test first. A hose puts out so much water that small details are hard to see. Be patient, get the knowledge first.

[nautilus]

KidHarris, Thank you so much for your thoughtful response! I guess I was just sealing the windows because I thought that is what I was supposed to do. The windows haven't leaked since we got the bus and when we removed the windows we didn't find any rust. The food coloring and spray bottle test make a lot sense. I am definitely going to do that once I re-install the windows to make sure I didn't create any places for the windows to leak up upon removing and re-installing. Thank you again for your educated advice! I really love this site.