Silicone vs polyurethane vs automotive sealer

[Gatheringminds7]

Aright y’all. Everyone seems to disagree on silicone vs polyurethane vs automotive sealant. I just want to buy one and I’m so tired of reading all the back and forth. Some of you scoff at silicone users and then they scoff at poly users. So who’s right and why?
Most important question: Which should I use when I’m screwing something into the side of the bus? I’d like to have the option to remove, so not tryin to use the concrete sealant type.
I keep hearing “add sealant before screws”, cool, got it, but WHICH SEALANT? I’d like to know what y’all have used and why. Name of the brand would be wildly appreciated and exactly what I’m needing: what exactly should I buy. I’m burning out on this back and forth, and beyond ready to finish the exterior of the bus.
I’m also adding some sealant around the lights up top. Slight leak on one, where light casing meets bus. So which sealant is best for that? And why? Again not trying to concrete these in Bc I’d like to completely remove them in the future. So I guess I’m wondering which would be easier to remove in the future?
Thank you!
Here’s some I’ve been looking at:
https://www.amazon.com/PL-Polyureth...&qid=1632196985&sprefix=Loctite+window&sr=8-4

https://www.amazon.com/gp/aw/d/B0012J3H1C/ref=ox_sc_act_image_1?smid=AYETLLJ1Q9FG5&psc=1

https://www.amazon.com/gp/aw/d/B004BPETG6/ref=ox_sc_act_image_3?smid=ATVPDKIKX0DER&psc=1

https://www.amazon.com/gp/aw/d/B001FC98X2/ref=ox_sc_act_image_1?smid=ATVPDKIKX0DER&psc=1

Thank you all in advance.

 

[Danjo-SKO]

Once you go poly you never go back

 

[rossvtaylor]

Once you go poly you never go back

Well, that wins the quote of the day!

I agree...polyurethane is the way to go. It won't get crumbly like silicone can. I'm old enough that I think I've experienced all the adhesive options out there and I'll never use anything but polyurethane adhesive/sealants on a customer's bus...and not on my own! It's more expensive, but I just got 6 more tubes of 3M 5200 for a roof raise project. I could have gone cheaper and, since I'm charging a flat rate, it would have increased my take home pay. But I don't ever want to hear that the seams leaked or gapped or that the silicone screwed up their paint job. Poly is worth it, I think.

EDIT to clarify...since you want to remove the windows someday. Don't use 3m 5200! It's as permanent as anything I've ever seen.

 

[Gatheringminds7]

Once you go poly you never go back

Heard that lol

 

[Gatheringminds7]

Well, that wins the quote of the day!

I agree...polyurethane is the way to go. It won't get crumbly like silicone can. I'm old enough that I think I've experienced all the adhesive options out there and I'll never use anything but polyurethane adhesive/sealants on a customer's bus...and not on my own! It's more expensive, but I just got 6 more tubes of 3M 5200 for a roof raise project. I could have gone cheaper and, since I'm charging a flat rate, it would have increased my take home pay. But I don't ever want to hear that the seams leaked or gapped or that the silicone screwed up their paint job. Poly is worth it, I think.

EDIT to clarify...since you want to remove the windows someday. Don't use 3m 5200! It's as permanent as anything I've ever seen.

That’s my conundrum: I don’t want to use super permanent for this stage, Bc I would like to remove eventually. I just don’t have time now for this aesthetic change. Trying to keep it simple and quick Bc I have a deadline for road ready and weather proofed. Since I’m looking to remove in the future, would you recommend going with silicone now, then polyurethane on permanent fixtures?

 

[DeMac]

Say No to Silicone

An important part of any sealant is how well it bonds to the two pieces it's meant to seal. If the product separates from either surface, the seal is no bueno. Ergo, some amount of adheasion must be involved.

Even within the scope of each of the major name brands of sealants and adheasives, there is no single recipie which will work both "best" and for all occasions.

Plastic lens to chrome,
glass to aluminum,
fiberglass to wood,
steel to steel,
low voc - interior,
uv protected - exterior,
hi-heat - engine bay,
paintable (latex, acrylic, oil),
self-leveling or vertical,
hi-solids for wider gaps,
elasticity & elongation,
clear or colored...
Best management practice: match products with their intended use. Reading through just one manufacture's sealant products info, helps to understand all of the specific variations and uses for each formulation.

Do you own a steel school bus or fiberglass shuttle?

Simalar to suggesting the best dish for food. A wide range of responses is expected.

Transportation Accessories Co. & Bus Parts Warehouse have the original foam light gaskets, which do crumble after a decade.

 

[Drew Bru]

Jeez. I guess Butyl rubber is the red-headed stepchild of sealants.

 

[rossvtaylor]

Jeez. I guess Butyl rubber is the red-headed stepchild of sealants.

Haha! Butyl tape is actually a good option for things the OP might want to remove later.

 

[DeMac]

Haha! Butyl tape is actually a good option for things the OP might want to remove later.

I absolutely agree with, Drew & Ross. Butyl tape makes a great water-tight seal, easy to work with, removable, inexpensive. Probably your best option, for a non permanent seal. (10 years?) Neither silicone nor urthane, buytl is a clay-based product.
We used about 280ft of butyl tape & rope to reseal Freddy's windows. The first two, which we reinstalled twice, removed & cleaned up easier than the factory seal.

It will compress about 40%, but wont thin out, so your gaps will be wider. Trim excess with an plastic razor blade.

 

[Rucker]

Well, that wins the quote of the day!

I agree...polyurethane is the way to go. It won't get crumbly like silicone can. I'm old enough that I think I've experienced all the adhesive options out there and I'll never use anything but polyurethane adhesive/sealants on a customer's bus...and not on my own! It's more expensive, but I just got 6 more tubes of 3M 5200 for a roof raise project. I could have gone cheaper and, since I'm charging a flat rate, it would have increased my take home pay. But I don't ever want to hear that the seams leaked or gapped or that the silicone screwed up their paint job. Poly is worth it, I think.

EDIT to clarify...since you want to remove the windows someday. Don't use 3m 5200! It's as permanent as anything I've ever seen.

Providing the silicone is not exposed, that is, that it is covered or in between things, any reason it doesn't qualify as a long term but removable seal?

I can see securing something with screws and using silicone for the sealant, underneath whatever is being secured.

 

[rossvtaylor]

Providing the silicone is not exposed, that is, that it is covered or in between things, any reason it doesn't qualify as a long term but removable seal?

I can see securing something with screws and using silicone for the sealant, underneath whatever is being secured.

It's "removable" but only if you cut it...which is a pain, but at least easier than poly. You won't be able to pull it apart. If it adheres properly in the first place, I definitely wouldn't consider it removable. Butyl tape is the better option for anything you might want to remove nondestructively.

 

[Gatheringminds7]

Thank you all for your input!! I worked out my situation to give me more time to do this right. So I’m going with the more permanent options. Also, gives me time to amp up the waterproofing on the windows which I’m stoked about Bc the original seal is hella cracked.

 

[DoubleO7]

If I am wanting to remove something in the future, don't want it to leak in the mean time and want the sealant to come off easily leaving no residue......

I would use butyl rubber tape. But most times that requires fasteners to hold the object in place.

 

[s2mikon]

I have seen a lot of the girls with the silicone ones, but I did not know you could get polyurethane ones. Do they hold up better?

 

[LargeMarge-TC]

Once you go poly, you never go back

.
And the corollary:
Once you go silicone, you keep coming back, a second layer then, inevitably, a fifteenth layer.

 

[LargeMarge-TC]

...silicone...any reason it doesn't qualify as a long term but removable seal?...

.
In my experience, silicone from a caulk-gun or a squeeze-tube is inadequate for jiggling parts such as we find on vehicles.
In my experience, silicone lacks stretch, so it shears the instant a jiggle occurs.
.
In my experience, silicone is not a "...removable seal...".
Silicone is near to impossible to remove.
You start with a putty-knife, you think 'maybe a chisel', and pretty soon, you graduate to nuclear warheads.
Years later, older and wiser, your tears of frustration bounce off the remaining streaks of silicone as it gloats in your face.
.
Inevitably, the siliconed project ends-up on craigslist as a 'you-finish'.
Of course, this does not take into consideration the tragic toil on family, friends, your employment.
Your mental health.

 

[Gatheringminds7]

Lame.
You could just not go there, that’d be a better choice.
-in response to s2mikon.

 

[Danjo-SKO]

Never mind.

 

[Gatheringminds7]

.
In my experience, silicone from a caulk-gun or a squeeze-tube is inadequate for jiggling parts such as we find on vehicles.
In my experience, silicone lacks stretch, so it shears the instant a jiggle occurs.
.
In my experience, silicone is not a "...removable seal...".
Silicone is near to impossible to remove.
You start with a putty-knife, you think 'maybe a chisel', and pretty soon, you graduate to nuclear warheads.
Years later, older and wiser, your tears of frustration bounce off the remaining streaks of silicone as it gloats in your face.
.
Inevitably, the siliconed project ends-up on craigslist as a 'you-finish'.
Of course, this does not take into consideration the tragic toil on family, friends, your employment.
Your mental health.

Nuclear warheads lol that whole bit
Thanks for explaining about it not stretching and shearing. That’s good reasoning for me not to use it.