Caulking (or, bedding/re-bedding as we'd say in the boating world). How can I resist?
Yes, I say fie on silicone. It doesn't work super well for what we're doing, and it is a bear to get off when you (will) need to re-seal the item. And as if that wasn't enough, it's the gift that keeps on giving with an invisible "silicone oil" contaminant that is next to impossible to remove. Good luck ever painting, or getting new bedding to stick -- or even getting more silicone to stick (as if you'd want to). Can you tell I love it?
Another thing that I find curious about the typical bedding job (done even by manufacturers and RV shops). They put bedding on TOP of the item. If there's anything that's hard on bedding/seals it's boats. They are almost never stored indoors, rarely in the shade, and when they move they twist and wrack. Plus "green water" often pours over them (i.e. not just rain or spray, but actual "solid" water). You can always tell when someone tried to put a "quick fix" on something that was leaking because you'll see caulking around the
outside of the item. This is not something you normally see on boats, because it basically doesn't work. So after a while they admit defeat and do it the proper way. I'm sure I sound high and mighty, but the proper way works! Putting caulk on top or around the edge is sort of like putting a band aid on your cut, then putting the Neosporin over the top and edges of the band aid
There can be variations here, depending on what one is bedding, the underlying surface and other details, but the basic idea is this:
1) Remove item that needs re-bedding (whether it be a preventative job or fixing a leak).
2) Clean up both surfaces (for example the underside of a window or roof vent flange, and the area of the RV that will be under the flange when you reinstall. This might involve scraping, solvents, and/or cursing (if there is silicone there
).
3) Choose a bedding compound. For the vast majority of things I'm bedding to fiberglass that also have mechanical fastening, I choose
good* butyl tape (bad butyl tape doesn't work very well). I have also used polyurethane, polysulfide, and polyether caulks in various circumstances.
4) Note that whichever bedding compound you choose may have specific solvent notes affecting the last prep step.
5) Mask off if desired (blue tape, etc.)
6) I like to clean fasteners, especially if new (they often have machine oil on them). Then if using butyl I'll make a little upside down cone of butyl under the head (this is the only sealant that you could say sort of goes on top).
7) Apply bedding (oftentimes to the bottom of the flange, but sometimes on the "deck," depending.
8) Tighten fasteners in appropriate pattern. If using butyl don't tighten "all the way," especially if it's cold out. Tighten to put some pressure on it, and then let that pressure "work" for a few days, then re-tighten, then maybe repeat. Anything like polyurethane that is "gooey" and cures I do tighten down all the way right away.
9) Clean up as appropriate (if butyl, you can wait until the last tightening; if something like polyurethane, I remove all squeeze out right away (you want to use plenty of polyurethane and get ample squeeze out. You can also clean up squeeze out from around the screw heads.
That's basically it. All your bedding is tidily protected under the flange, where its doing its job.
Any specific questions I can try to answer.
Here is a good tutorial from a sailor. I tried to keep it simple above, so didn't say everything, but he has some good additional tips on beveling the holes, and etc. Another consideration is closing out the core in cored areas, but that's perhaps "TMI" at the moment.
http://www.pbase.com/mainecruising/rebedding_hardware
He also sells the good butyl tape (only place I can find it anymore, and I've tried quite a few):
http://www.pbase.com/mainecruising/buy_bedit_butyl_tape