I used to work with glass (aquarium, etc.) so I am a fan of silicone. But I guess some of you don't like to use it on the Chinook. I wonder what is the better alternative to get to glue the water heater door to the body, etc?
I see there are some caulking on top of screws on the vent on the top. What should I get to seal them?
silicone alternatives
silicone alternatives
2000 Concourse dinette, on 1999 6.8L Ford E350 Triton V-10 Chassis
Re: silicone alternatives
If silicone caulk ever needs to be removed, it can be pretty stubborn. And when you finally do get it off, it leaves a film which basically nothing will stick to, including more silicone. Most of us have probably suffered through this a few times. I've spec'd molded silicone in many industrial applications, and it has some great properties, especially when high heat electrical insulation is needed, or tubing and o-rings. But as a caulked sealant, it's kind of a band aid (lazy) solution. The stuff on your roof fasteners is most likely lap sealant. Not an ideal approach, but it's an industry standard. For your water heater door, I'd use butyl tape. I'm sure Blue will explain further! 
1994 Premier
Re: silicone alternatives
Well hello, hello
I'm so glad you asked. Yeah, silicone is bad for a number of reasons, IMO. First of all, it's not that great at doing the job at hand. Second, as Scott mentions, have fun ever removing it, and even when you can't see it anymore, the residue left behind will make adhering anything else nigh on to impossible for, oh, a thousand years or so. Seriously though, some boaters have resorted to grinding the gelcoat off just to get rid of it. There isn't much I can think of that I'd less like to see on a boat, RV, etc.
So, what TO use? There are a number of options, and sometimes one or another product is clearly a big benefit or a no-go, but oftentimes you can choose amongst a few.
Butyl is near and dear to my heart (but only GOOD butyl*). Why do I like it so much? It does the job extremely well, lasts darned near forever (both doing the job and on the roll in storage), doesn't make a mess when you apply it, and -- best of all -- is an absolute cinch to remove when the time comes (and it often does come: A part you bedded in place breaks, you want to upgrade, etc.).
But butyl isn't right for everything. One, it's vulnerable to fuel (not a big deal on an RV, but you wouldn't, say, use it to bed fuel fills on a boat). Two, it can continue to ooze out a bit for awhile, and also would prefer to be tightened down slowly, over a period of a day or a week. The "ooze" is easy to clean off, but still there are cases that wouldn't work. Also, it is not an adhesive: You want to use it on things that are also mechanically fastened (screws, etc.).
Another choice would be polyurethane. Examples are 3M 4200 and 5200, Sikaflex 291, and others. These are adhesives and caulks together. That can be good or bad. I've had a crew just about tear the transom off a boat trying to get a broken swim platform off (it was stuck on with 5200). There are a few times that level of adhesion is needed, but they are very few. 4200 is still quite adhesive, but not as much as 4200. But they have their downsides too. One, they can be messy to work with, two, they can be hard to remove, and three, they yellow in UV light. But they do set up "permanently" which can be an advantage in some situations (it takes a while though).
Polyether is another choice (3M 4000). It's in some ways similar to polyurethane, but isn't supposed to yellow in UV light. I've only used it a half dozen times (on boat stuff), and don't have long term experience to speak to how it removes, etc. (has only been on four years or so).
On the "stuff on top" phenomenon: That one puzzles me. As Scott says, it's the RV standard. You bed the item (i.e. product of choice under the flange), then fasten it down (okay, so far so good), and THEN pour a bunch of self leveling gumbo over the top. You might for good measure run a bead around the outside too. It seems strange to me because that is never done on boats, and heaven knows they take on a LOT more water (solid water even, not just spray) than an RV, and they flex in a seaway as well. They can also sink. On boats you bed under the flange, then use some sealant under the fastener heads (but clean it off after you tighten the fasteners). In the end, basically no sealant shows. Nothing to trap dirt or debris, no globs. This even holds true for fittings beneath the waterline. The only time you'll see sealant on top of a fitting on a boat is when someone has a leak for some reason and they try a band-aid fix. But before long they'll remove the fitting and do it the right way, because it never really works (boats can easily last a half century or more, so things do get re-bedded a few times through their lifetime).
I suppose partly it might be that the flanges on many RV things are thin and flimsy (I'm looking at you, Fantastic Vents - although it's not just them). That makes it harder to bed properly under the flange. Also, on some RV's (not ours), you can't chamfer fastener holes under the flange to accept a "ring" of sealant -- but you can on our gelcoated/fiberglass.
Anyway, hopefully not too much information.
BG
*I have tested a number of butyl products and have only found one that has measured up to the "good old" stuff I have from decades ago that is still pliable, and still stretches feet without breaking. The others looked like butyl, but were more like putty or clay when put to the test. The one I use is called Bed-It. Basically, a fellow sailor found the same thing I did, but he went to a mfgr and had them start making it to his specifications. Great stuff! And it lasts forever even on the roll (which you can't say about the things in a tube, especially once they are opened).
I'm so glad you asked. Yeah, silicone is bad for a number of reasons, IMO. First of all, it's not that great at doing the job at hand. Second, as Scott mentions, have fun ever removing it, and even when you can't see it anymore, the residue left behind will make adhering anything else nigh on to impossible for, oh, a thousand years or so. Seriously though, some boaters have resorted to grinding the gelcoat off just to get rid of it. There isn't much I can think of that I'd less like to see on a boat, RV, etc.
So, what TO use? There are a number of options, and sometimes one or another product is clearly a big benefit or a no-go, but oftentimes you can choose amongst a few.
Butyl is near and dear to my heart (but only GOOD butyl*). Why do I like it so much? It does the job extremely well, lasts darned near forever (both doing the job and on the roll in storage), doesn't make a mess when you apply it, and -- best of all -- is an absolute cinch to remove when the time comes (and it often does come: A part you bedded in place breaks, you want to upgrade, etc.).
But butyl isn't right for everything. One, it's vulnerable to fuel (not a big deal on an RV, but you wouldn't, say, use it to bed fuel fills on a boat). Two, it can continue to ooze out a bit for awhile, and also would prefer to be tightened down slowly, over a period of a day or a week. The "ooze" is easy to clean off, but still there are cases that wouldn't work. Also, it is not an adhesive: You want to use it on things that are also mechanically fastened (screws, etc.).
Another choice would be polyurethane. Examples are 3M 4200 and 5200, Sikaflex 291, and others. These are adhesives and caulks together. That can be good or bad. I've had a crew just about tear the transom off a boat trying to get a broken swim platform off (it was stuck on with 5200). There are a few times that level of adhesion is needed, but they are very few. 4200 is still quite adhesive, but not as much as 4200. But they have their downsides too. One, they can be messy to work with, two, they can be hard to remove, and three, they yellow in UV light. But they do set up "permanently" which can be an advantage in some situations (it takes a while though).
Polyether is another choice (3M 4000). It's in some ways similar to polyurethane, but isn't supposed to yellow in UV light. I've only used it a half dozen times (on boat stuff), and don't have long term experience to speak to how it removes, etc. (has only been on four years or so).
On the "stuff on top" phenomenon: That one puzzles me. As Scott says, it's the RV standard. You bed the item (i.e. product of choice under the flange), then fasten it down (okay, so far so good), and THEN pour a bunch of self leveling gumbo over the top. You might for good measure run a bead around the outside too. It seems strange to me because that is never done on boats, and heaven knows they take on a LOT more water (solid water even, not just spray) than an RV, and they flex in a seaway as well. They can also sink. On boats you bed under the flange, then use some sealant under the fastener heads (but clean it off after you tighten the fasteners). In the end, basically no sealant shows. Nothing to trap dirt or debris, no globs. This even holds true for fittings beneath the waterline. The only time you'll see sealant on top of a fitting on a boat is when someone has a leak for some reason and they try a band-aid fix. But before long they'll remove the fitting and do it the right way, because it never really works (boats can easily last a half century or more, so things do get re-bedded a few times through their lifetime).
I suppose partly it might be that the flanges on many RV things are thin and flimsy (I'm looking at you, Fantastic Vents - although it's not just them). That makes it harder to bed properly under the flange. Also, on some RV's (not ours), you can't chamfer fastener holes under the flange to accept a "ring" of sealant -- but you can on our gelcoated/fiberglass.
Anyway, hopefully not too much information.
BG
*I have tested a number of butyl products and have only found one that has measured up to the "good old" stuff I have from decades ago that is still pliable, and still stretches feet without breaking. The others looked like butyl, but were more like putty or clay when put to the test. The one I use is called Bed-It. Basically, a fellow sailor found the same thing I did, but he went to a mfgr and had them start making it to his specifications. Great stuff! And it lasts forever even on the roll (which you can't say about the things in a tube, especially once they are opened).
1999 Concourse
Re: silicone alternatives
Thank you, Blue, but I never have too much info!
So 3M 5200 is a lot strong than 3M 4200?
I think there is a link for the Bed-It somewhere here, but do you have it handy? I am going to order some.
I also would like to see a video or detail instruction of how to chamfer fastener holes, and apply the sealant so that I don't have to peel off the gooey goop to get to the fasteners. I think I know how to do it, just maybe there is some gotcha that I may not know.
So 3M 5200 is a lot strong than 3M 4200?
I think there is a link for the Bed-It somewhere here, but do you have it handy? I am going to order some.
I also would like to see a video or detail instruction of how to chamfer fastener holes, and apply the sealant so that I don't have to peel off the gooey goop to get to the fasteners. I think I know how to do it, just maybe there is some gotcha that I may not know.
2000 Concourse dinette, on 1999 6.8L Ford E350 Triton V-10 Chassis
Re: silicone alternatives
You have it right: 4200 is basically the same ting as 5200, but 5200 is a LOT more adhesive. Like, "permanent" adhesive. Yes, it can be removed, but you often destroy what you're removing or what you're removing it from. And really, I can't think of anything off the top of my head that needs to be that permanent on an RV, after it's been initially built (it's not that the "sealing" part is necessarily so permanent, just the adhesive part).
Anyway, on to butyl! Here is a link for Bed-It:
https://shop.marinehowto.com/products/bed-it-tape
Interestingly, I see it's now being sold through some other good marine vendors, such as Hamilton Marine. I'll still continue buying it from the source though, because it's a way to thank him for the excellent tutorials he puts together (I use the same methods, but I could never put together as good a tutorial).
Here is one on bedding marine fittings with butyl tape, which also shows the chamfering. The idea is to give a little place for an "o-ring" of sealant to be (vs. smushing it all out). Conveniently, it's also a really good thing to do on gelcoat (which is what's on the outside surface of our Chinooks) because if you just drill a regular hole and don't chamfer, you'll often get chipping and radiating cracks (as I've found on just about all of the original holes on the Chinook). While it's best to chamfer in the first place, doing it now will often eclipse the previous damage and keep it from spreading (plus you get the little well for sealant).
https://marinehowto.com/bed-it-tape/
In case you still have popcorn in the bowl and are interested, here is one on sealing deck core (can apply to certain places on the Chinook where there is plywood roof core):
https://marinehowto.com/sealing-deck-pe ... -core-rot/
RC (who makes the tutorials and sells Bed-It) is a fellow sailor and boat worker. He has some very good electrical tutorials as well. He's careful and conscientious and knows his stuff.
Anyway, on to butyl! Here is a link for Bed-It:
https://shop.marinehowto.com/products/bed-it-tape
Interestingly, I see it's now being sold through some other good marine vendors, such as Hamilton Marine. I'll still continue buying it from the source though, because it's a way to thank him for the excellent tutorials he puts together (I use the same methods, but I could never put together as good a tutorial).
Here is one on bedding marine fittings with butyl tape, which also shows the chamfering. The idea is to give a little place for an "o-ring" of sealant to be (vs. smushing it all out). Conveniently, it's also a really good thing to do on gelcoat (which is what's on the outside surface of our Chinooks) because if you just drill a regular hole and don't chamfer, you'll often get chipping and radiating cracks (as I've found on just about all of the original holes on the Chinook). While it's best to chamfer in the first place, doing it now will often eclipse the previous damage and keep it from spreading (plus you get the little well for sealant).
https://marinehowto.com/bed-it-tape/
In case you still have popcorn in the bowl and are interested, here is one on sealing deck core (can apply to certain places on the Chinook where there is plywood roof core):
https://marinehowto.com/sealing-deck-pe ... -core-rot/
RC (who makes the tutorials and sells Bed-It) is a fellow sailor and boat worker. He has some very good electrical tutorials as well. He's careful and conscientious and knows his stuff.
1999 Concourse